# Spiral Staircase: the full register > Every graded claim with its verdict, evidence and sources; each of the book's 16 chapters with its start-here actions and mismatch card; the 30-day protocol; and the glossary. From Spiral Staircase, Revised Second Edition (2026), by Neil P. Bostick. The shorter guide is https://www.spiralstaircase.com/llms.txt. Grades, as the book defines them: - Strong: Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism. - Probable: Good observational evidence with a plausible mechanism, or small or few trials. - Emerging: Early, small, animal-only, or actively contested. A claim quoted without its grade has had the most useful part removed. Nothing here is medical advice. Cite as: Bostick, N.P. (2026). Spiral Staircase: How Your Ancient Body Navigates the Modern World, Revised Second Edition. ISBN 9798176270860. ## Popular claims, graded ### Are seed oils inflammatory? What the trials show URL: https://www.spiralstaircase.com/verdicts/avoid-seed-oils-to-lower-inflammation Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Avoid seed oils to lower inflammation. Verdict: Against, as stated. Evidence grade: Probable. Evidence: A systematic review of randomized trials found that linoleic acid, the omega-6 fat plentiful in seed oils, had no significant effect on blood markers of inflammation in healthy adults. It does not speak to existing metabolic disease (Chapter 5). Sources (note numbers of Chapter 2): - Johnson, G.H., and Fritsche, K. (2012). "Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials." Journal of the Academy of Nutrition and Dietetics, 112(7), 1029-1041. https://doi.org/10.1016/j.jand.2012.03.029 (15 randomized controlled trials) Tested again in a "What you've heard" box: Chapter 5, Eat (https://www.spiralstaircase.com/book/5-eat) Claim: Seed oils such as soybean, corn and canola are inflammatory poisons behind modern disease. Verdict: Unsupported as stated. Evolutionary novelty is not evidence of harm. Evidence grade: Probable. Evidence: Seed oils are a genuinely modern, high-volume food, and that novelty is the core of the case against them. When trials added linoleic acid, the main fat in these oils, to healthy people's diets, inflammatory markers did not rise. In cohorts across many countries, people with more linoleic acid in their blood had less heart disease and less diabetes, and in a large US cohort butter was linked to higher mortality and plant oils to lower. The other side deserves a fair hearing: data recovered from two trials run half a century ago found no benefit, and in one a hint of harm, when vegetable oil replaced saturated fat, and a major review found that more of this kind of fat may make little or no difference to deaths either way. Frying oil reused for hours, and the fried ultra-processed food it ends up in, are separate problems. Sources (note numbers of Chapter 5): - Johnson, G.H., and Fritsche, K. (2012). "Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials." Journal of the Academy of Nutrition and Dietetics, 112(7), 1029-1041.e15. https://doi.org/10.1016/j.jand.2012.03.029; Marklund, M., Wu, J.H.Y., Imamura, F., Del Gobbo, L.C., et al. (2019). "Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality." Circulation, 139(21), 2422-2436. https://doi.org/10.1161/CIRCULATIONAHA.118.038908; Wu, J.H.Y., Marklund, M., Imamura, F., Tintle, N., et al. (2017). "Omega-6 fatty acid biomarkers and incident type 2 diabetes: pooled analysis of individual-level data for 39 740 adults from 20 prospective cohort studies." Lancet Diabetes and Endocrinology, 5(12), 965-974. https://doi.org/10.1016/S2213-8587(17)30307-8; Zhang, Y., Chadaideh, K.S., Li, Y., Li, Y., et al. (2025). "Butter and plant-based oils intake and mortality." JAMA Internal Medicine, 185(5), 549-560. https://doi.org/10.1001/jamainternmed.2025.0205; Ramsden, C.E., Zamora, D., Leelarthaepin, B., Majchrzak-Hong, S.F., et al. (2013). "Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis." BMJ, 346, e8707. https://doi.org/10.1136/bmj.e8707; Hooper, L., Al-Khudairy, L., Abdelhamid, A.S., Rees, K., et al. (2018). "Omega-6 fats for the primary and secondary prevention of cardiovascular disease." Cochrane Database of Systematic Reviews, 11, CD011094. https://doi.org/10.1002/14651858.CD011094.pub4 (19 trials, 6,461 people; low to very low quality); Ramsden, C.E., Zamora, D., Majchrzak-Hong, S., Faurot, K.R., et al. (2016). "Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)." BMJ, 353, i1246. https://doi.org/10.1136/bmj.i1246 (fifteen randomized trials in the inflammation review) ### Is raw milk healthier or safe? URL: https://www.spiralstaircase.com/verdicts/drink-raw-milk Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Drink raw milk. Verdict: Against, and the risk is measured. Evidence grade: Probable. Evidence: Unpasteurized milk and cheese are eaten by a small minority of Americans, yet they accounted for 96% of the illnesses from dairy outbreaks (Chapter 6). Sources (note numbers of Chapter 2): - Costard, S., Espejo, L., Groenendaal, H., and Zagmutt, F.J. (2017). "Outbreak-related disease burden associated with consumption of unpasteurized cow's milk and cheese, United States, 2009-2014." Emerging Infectious Diseases, 23(6), 957-964. https://doi.org/10.3201/eid2306.151603 (raw milk is consumed by 3.2% and unpasteurized cheese by 1.6% of the US population) Tested again in a "What you've heard" box: Chapter 6, The Gut That Expects Dirt (https://www.spiralstaircase.com/book/6-the-gut-that-expects-dirt) Claim: Raw milk is healthier. Verdict: Unsupported, and the risk is measured. Evidence grade: Probable. Evidence: In a large European study of farm children, drinking farm milk was linked to less asthma. But the link was observational, and boiled farm milk showed no such link. The infection risk, by contrast, is counted. In the United States, a small minority of people drink raw milk or eat unpasteurized cheese, yet unpasteurized dairy caused 96% of the illnesses in dairy-linked outbreaks. Raw milk can carry Listeria, E. coli and other germs most dangerous to young children, pregnant women, older adults and anyone with weakened immunity. Sources (note numbers of Chapter 6): - Loss, G., Apprich, S., Waser, M., Kneifel, W., et al. (2011). "The protective effect of farm milk consumption on childhood asthma and atopy: the GABRIELA study." Journal of Allergy and Clinical Immunology, 128(4), 766-773.e4. https://doi.org/10.1016/j.jaci.2011.07.048 (8,334 rural schoolchildren); Costard, S., Espejo, L., Groenendaal, H., and Zagmutt, F.J. (2017). "Outbreak-related disease burden associated with consumption of unpasteurized cow's milk and cheese, United States, 2009-2014." Emerging Infectious Diseases, 23(6), 957-964. https://doi.org/10.3201/eid2306.151603 (3.2% of Americans drink raw milk and 1.6% eat unpasteurized cheese; 96% of illnesses in dairy-linked outbreaks, 2009-2014); Centers for Disease Control and Prevention (2025). Raw milk (last reviewed 31 January 2025). https://www.cdc.gov/food-safety/foods/raw-milk.html; Centers for Disease Control and Prevention (n.d.). Preventing Listeria Infection. https://www.cdc.gov/listeria/prevention/index.html (higher risk in pregnancy, over 65 and with weakened immunity) ### Does grounding work, or is it pseudoscience? URL: https://www.spiralstaircase.com/verdicts/grounding-or-earthing Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Grounding, or earthing. Verdict: Emerging and contested. Evidence grade: Emerging. Evidence: Skin contact with the earth is said to transfer electrons and reduce inflammation. The idea rests on reviews written by its advocates, with no large independent trials (Chapter 10). Sources (note numbers of Chapter 2): - Chevalier, G., Sinatra, S.T., Oschman, J.L., Sokal, K., et al. (2012). "Earthing: health implications of reconnecting the human body to the earth's surface electrons." Journal of Environmental and Public Health, 2012, 291541. https://doi.org/10.1155/2012/291541 ; Oschman, J.L., Chevalier, G., and Brown, R. (2015). "The effects of grounding (earthing) on inflammation, the immune response, wound healing, and prevention and treatment of chronic inflammatory and autoimmune diseases." Journal of Inflammation Research, 8, 83-96. https://doi.org/10.2147/JIR.S69656 (narrative reviews by authors who advocate the practice) Tested again in a "What you've heard" box: Chapter 10, Green and Quiet (https://www.spiralstaircase.com/book/10-green-and-quiet) Claim: Walking barefoot on the earth, or sleeping on a grounding mat, lets electrons flow into your body and reduces inflammation. Verdict: Unsupported. Evidence grade: Emerging. Evidence: The case for grounding rests on narrative reviews written by the practice's advocates, some of whom disclose contractor roles and small shareholdings in a grounding company. A key study of muscle soreness grounded four people. A later trial relied on the self-reports of sixteen massage therapists. No adequately sized, independent trial with a sham device has been published. Grass underfoot is pleasant, and a walk in a park has real evidence behind it, but none of that evidence runs through electrons. Sources (note numbers of Chapter 10): - Chevalier, G., Sinatra, S.T., Oschman, J.L., Sokal, K., and Sokal, P. (2012). "Earthing: health implications of reconnecting the human body to the earth's surface electrons." Journal of Environmental and Public Health, 2012, 291541. https://doi.org/10.1155/2012/291541 ; Oschman, J.L., Chevalier, G., and Brown, R. (2015). "The effects of grounding (earthing) on inflammation, the immune response, wound healing, and prevention and treatment of chronic inflammatory and autoimmune diseases." Journal of Inflammation Research, 8, 83-96. https://doi.org/10.2147/JIR.S69656 ; Brown, D., Chevalier, G., and Hill, M. (2010). "Pilot study on the effect of grounding on delayed-onset muscle soreness." Journal of Alternative and Complementary Medicine, 16(3), 265-273. https://doi.org/10.1089/acm.2009.0399 ; Chevalier, G., Patel, S., Weiss, L., Chopra, D., et al. (2019). "The effects of grounding (earthing) on bodyworkers' pain and overall quality of life: a randomized controlled trial." Explore, 15(3), 181-190. https://doi.org/10.1016/j.explore.2018.10.001 ### Is the carnivore diet supported by evidence? URL: https://www.spiralstaircase.com/verdicts/carnivore-diet Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Carnivore diet. Verdict: Self-reported only, no trials. Evidence grade: Emerging. Evidence: In a large survey of adults on the diet, nearly all reported better health. There was no control group, the participants chose themselves, and their LDL cholesterol, the kind that builds up in arteries, was typically high, so long-term heart safety is untested. Sources (note numbers of Chapter 2): - Lennerz, B.S., Mey, J.T., Henn, O.H., and Ludwig, D.S. (2021). "Behavioral characteristics and self-reported health status among 2029 adults consuming a 'carnivore diet'." Current Developments in Nutrition, 5(12), nzab133. https://doi.org/10.1093/cdn/nzab133 (95% reported better overall health; median LDL cholesterol was 172 mg/dL) ### Is mouth taping safe, and does it work? URL: https://www.spiralstaircase.com/verdicts/mouth-taping Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Mouth taping. Verdict: Unsupported, with a safety catch. Evidence grade: Emerging. Evidence: In a systematic review of ten small studies, two showed some improvement in apnea measures and the rest none, and the reviewers warned of a risk of harm, including suffocation, when the nose is blocked. Tape can also hide the snoring that signals sleep apnea, so get checked first (Chapter 8). Sources (note numbers of Chapter 2): - Rhee, J., Iansavitchene, A., Mannala, S., Graham, M.E., et al. (2025). "Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: a systematic review." PLOS ONE, 20(5), e0323643. https://doi.org/10.1371/journal.pone.0323643 Tested again in a "What you've heard" box: Chapter 8, Sleep (https://www.spiralstaircase.com/book/8-sleep) Claim: Taping your mouth shut at night improves sleep and breathing. Verdict: Unsupported for self-treatment, and possibly risky. Evidence grade: Emerging for any benefit; avoid it unless a clinician directs it alongside CPAP. Evidence: A recent systematic review found ten small studies. Two showed some improvement in apnea measures; the rest found no difference, and the reviewers warned of a potentially serious risk of harm, including suffocation, in people whose noses are blocked. Tape also hides the snoring that should send someone to a doctor. In one clinical niche, under a clinician's direction, it helped people who breathe through the mouth use their CPAP masks longer. Sources (note numbers of Chapter 8): - Rhee, J., Iansavitchene, A., Mannala, S., Graham, M.E., et al. (2025). "Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: a systematic review." PLOS ONE, 20(5), e0323643. https://doi.org/10.1371/journal.pone.0323643 (Ten studies, about two hundred patients in all.) ; Meksukree, A., Pitipanyakul, S., Laohavinij, W., et al. (2025). "The role of mouth tape for CPAP use in patients with mouth breathing and OSA." Journal of Clinical Sleep Medicine, 21(12), 2063-2071. https://doi.org/10.5664/jcsm.11870 (Randomized crossover in 62 CPAP users who breathe through the mouth.) ### Do barefoot shoes fix your feet? URL: https://www.spiralstaircase.com/verdicts/barefoot-and-minimal-shoes Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Barefoot and minimal shoes. Verdict: Probable for foot strength; unsupported for injury prevention. Evidence grade: Probable for strength; Emerging for injuries. Evidence: Eight weeks of walking in minimal shoes increased foot muscle size and strength in runners, and six months of minimal footwear raised foot strength by more than half. Injury prevention lacks large controlled trials (Chapter 3). Sources (note numbers of Chapter 2): - Ridge, S.T., Olsen, M.T., Bruening, D.A., and Jurgensmeier, K. (2019). "Walking in minimalist shoes is effective for strengthening foot muscles." Medicine and Science in Sports and Exercise, 51(1), 104-113. https://doi.org/10.1249/MSS.0000000000001751 (eight weeks, runners) ; Curtis, R., Willems, C., Paoletti, P., and D'Août, K. (2021). "Daily activity in minimal footwear increases foot strength." Scientific Reports, 11, 18648. https://doi.org/10.1038/s41598-021-98070-0 (six months; foot strength rose 57.4%) Tested again in a "What you've heard" box: Chapter 3, The Body That Walks (https://www.spiralstaircase.com/book/3-the-body-that-walks) Claim: Barefoot or minimalist shoes fix your feet. Verdict: Stronger feet, yes, slowly; fewer injuries or better balance, unproven. Evidence grade: Probable for foot strength; Emerging for injuries and balance. Evidence: Partly. In small trials, walking in thin, flexible shoes built foot muscle about as well as foot exercises, though a review rated the evidence low to very low certainty. For injuries, a Cochrane review found no clear reduction in running injuries from any type of running shoe, and when a small group of runners switched to toe-shoes over ten weeks, more than half showed new fluid in a foot bone on scans. The famous study of barefoot runners that launched the fashion measured impact forces, not injuries, and was part-funded by a shoe maker. For older feet, falls matter most: going barefoot or in socks at home is linked to more falls, while exercise combining balance and strength cut the rate of falls by about a third in pooled trials. Sources (note numbers of Chapter 3): - Ridge, S.T., Olsen, M.T., Bruening, D.A., Jurgensmeier, K., et al. (2019). "Walking in minimalist shoes is effective for strengthening foot muscles." Medicine and Science in Sports and Exercise, 51(1), 104-113. https://doi.org/10.1249/MSS.0000000000001751 ; Peters-Dickie, J.L., Detrembleur, C., Guallar-Bouloc, M., Rastelli, M., et al. (2025). "The effects of foot core exercises and minimalist footwear on foot muscle sizes, foot strength, and biomechanics: a systematic review and meta-analysis." Clinical Biomechanics, 122, 106417. https://doi.org/10.1016/j.clinbiomech.2024.106417 ; Relph, N., Greaves, H., Armstrong, R., Prior, T.D., et al. (2022). "Running shoes for preventing lower limb running injuries in adults." Cochrane Database of Systematic Reviews, 8, CD013368. https://doi.org/10.1002/14651858.CD013368.pub2 ; Ridge, S.T., Johnson, A.W., Mitchell, U.H., Hunter, I., et al. (2013). "Foot bone marrow edema after a 10-wk transition to minimalist running shoes." Medicine and Science in Sports and Exercise, 45(7), 1363-1368. https://doi.org/10.1249/MSS.0b013e3182874769 (10 of 19 runners) ; Lieberman, D.E., Venkadesan, M., Werbel, W.A., Daoud, A.I., et al. (2010). "Foot strike patterns and collision forces in habitually barefoot versus shod runners." Nature, 463(7280), 531-535. https://doi.org/10.1038/nature08723 ; Koepsell, T.D., Wolf, M.E., Buchner, D.M., Kukull, W.A., et al. (2004). "Footwear style and risk of falls in older adults." Journal of the American Geriatrics Society, 52(9), 1495-1501. https://doi.org/10.1111/j.1532-5415.2004.52412.x ; Sherrington, C., Fairhall, N.J., Wallbank, G.K., Tiedemann, A., et al. (2019). "Exercise for preventing falls in older people living in the community." Cochrane Database of Systematic Reviews, 1, CD012424. https://doi.org/10.1002/14651858.CD012424.pub2 . Vibram USA helped fund the 2010 Nature study; Koepsell studied people aged 65 and over. ### Do cold plunges do anything? URL: https://www.spiralstaircase.com/verdicts/cold-plunges Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Cold plunges. Verdict: A narrow effect on heat regulation; nothing on fat loss. Evidence grade: Emerging for both. Evidence: Eight Scandinavian winter swimmers, compared with eight controls, regulated body heat differently and made more heat in the cold. The study found no increase in brown fat and says nothing about weight loss. Chapter 9 gives the cautions about cold shock and the heart. Sources (note numbers of Chapter 2): - Søberg, S., et al. (2021). Cell Reports Medicine, 2, 100408 (Scandinavian winter swimmers combining cold water and sauna, 8 against 8 controls; do not read as more brown fat) ### Is sunscreen bad for you? URL: https://www.spiralstaircase.com/verdicts/avoid-sunscreen Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Avoid sunscreen. Verdict: Against: the one trial runs the other way. Evidence grade: Probable, a single trial with few melanomas. Evidence: An Australian trial assigned adults to use sunscreen daily or at their own discretion. Over long follow-up the daily group had three invasive melanomas, the most dangerous skin cancer, against eleven in the other group (Chapter 7). Sources (note numbers of Chapter 2): - Green, A.C., Williams, G.M., Logan, V., and Strutton, G.M. (2011). "Reduced melanoma after regular sunscreen use: randomized trial follow-up." Journal of Clinical Oncology, 29(3), 257-263. https://doi.org/10.1200/JCO.2010.28.7078 (the Nambour trial: 1,621 adults randomized in 1992-96 and followed to 2006; hazard ratio for invasive melanoma 0.27, 95% CI 0.08-0.97) Tested again in a "What you've heard" box: Chapter 7, Light and Dark (https://www.spiralstaircase.com/book/7-light-and-dark) Claim: Sunscreen is dangerous, and you are better off without it. Verdict: The danger claim is unsupported, and the one long trial runs the other way. Evidence grade: Strong that the claim fails; Probable for sunscreen against melanoma. Evidence: In trials run by the US Food and Drug Administration, heavy, repeated use put several chemical filters into the blood above the level that prompts further safety testing. The agency has not concluded that those ingredients are unsafe. Against that sits a randomized trial in Nambour, Queensland, where adults were assigned to put on sunscreen every day or as they pleased. The daily group developed about two-fifths fewer squamous cell tumors, though no fewer people got one, and a decade after the trial ended, it had three invasive melanomas against eleven, a small count. If the worry is vitamin D, a daily supplement settles it without giving up sunscreen. If you want less on your skin, lean on shade, clothing and a hat first. Sources (note numbers of Chapter 7): - Matta, M.K., Zusterzeel, R., Pilli, N.R., Patel, V., et al. (2019). "Effect of sunscreen application under maximal use conditions on plasma concentration of sunscreen active ingredients: a randomized clinical trial." JAMA, 321(21), 2082-2091. https://doi.org/10.1001/jama.2019.5586 ; U.S. Food and Drug Administration (2026). Questions and answers: FDA's regulatory actions on over-the-counter sunscreen. https://www.fda.gov/drugs/understanding-over-counter-medicines/questions-and-answers-fdas-regulatory-actions-over-counter-sunscreen ; Green, A., Williams, G., Neale, R., Hart, V., et al. (1999). "Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial." The Lancet, 354(9180), 723-729. https://doi.org/10.1016/S0140-6736(98)12168-2 (1,621 adults. Tumors, rate ratio 0.61; people with a new squamous cell cancer, 0.88, 95% CI 0.50-1.56.) ; Green, A.C., Williams, G.M., Logan, V., and Strutton, G.M. (2011). "Reduced melanoma after regular sunscreen use: randomized trial follow-up." Journal of Clinical Oncology, 29(3), 257-263. https://doi.org/10.1200/JCO.2010.28.7078 (Invasive melanoma hazard ratio 0.27, 95% CI 0.08-0.97; all melanomas 0.50, 0.24-1.02.) ### Do detox teas and juice cleanses work? URL: https://www.spiralstaircase.com/verdicts/detox-teas-juice-cleanses-and-similar Tested in Chapter 2's table of nine claims: Chapter 2, What Your Body Expects, and How to Trust This Book (https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book) Claim: Detox teas, juice cleanses and similar. Verdict: Unsupported. Evidence grade: None; there are no primary studies to grade. Evidence: No controlled trial shows that these products improve on what a working liver and kidneys already do. With no primary studies to check, the absence is the finding. ### Is sitting the new smoking? URL: https://www.spiralstaircase.com/verdicts/sitting-is-the-new-smoking Tested in a "What you've heard" box: Chapter 3, The Body That Walks (https://www.spiralstaircase.com/book/3-the-body-that-walks) Claim: Sitting is the new smoking. Verdict: Exaggerated about tenfold. Break up sitting, but above all, move more. Evidence grade: Probable. Evidence: Long sitting is linked to higher death rates, but the comparison with cigarettes is not close. Against never-smokers, the heaviest smokers suffer more than two thousand extra deaths per hundred thousand people a year; the heaviest sitters, against the lightest, about two hundred. That extra risk can be bought back: in pooled data on more than a million people, those who sat over eight hours a day but did roughly an hour or more of moderate activity daily had no clear excess risk. Five or more hours of daily television stayed linked to higher risk even in the most active. Standing all day is no cure either: it burns barely more than sitting, and long hours of it are linked to varicose veins. Sit-stand desks cut workplace sitting at first, but their trials measured sitting, not disease. Sources (note numbers of Chapter 3): - Vallance, J.K., Gardiner, P.A., Lynch, B.M., D'Silva, A., et al. (2018). "Evaluating the evidence on sitting, smoking, and health: is sitting really the new smoking?" American Journal of Public Health, 108(11), 1478-1482. https://doi.org/10.2105/AJPH.2018.304649 ; Ekelund, U., Steene-Johannessen, J., Brown, W.J., Fagerland, M.W., et al. (2016). "Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women." The Lancet, 388(10051), 1302-1310. https://doi.org/10.1016/S0140-6736(16)30370-1 ; Saeidifard, F., Medina-Inojosa, J.R., Supervia, M., Olson, T.P., et al. (2018). "Differences of energy expenditure while sitting versus standing: a systematic review and meta-analysis." European Journal of Preventive Cardiology, 25(5), 522-538. https://doi.org/10.1177/2047487317752186 ; Ahmadi, M.N., Coenen, P., Straker, L., and Stamatakis, E. (2024). "Device-measured stationary behaviour and cardiovascular and orthostatic circulatory disease incidence." International Journal of Epidemiology, 53(6), dyae136. https://doi.org/10.1093/ije/dyae136 ; Shrestha, N., Kukkonen-Harjula, K.T., Verbeek, J.H., Ijaz, S., et al. (2018). "Workplace interventions for reducing sitting at work." Cochrane Database of Systematic Reviews, 12, CD010912. https://doi.org/10.1002/14651858.CD010912.pub5 . The smoking and sitting figures are more than 2,000 against about 190 extra deaths per 100,000. ### Is 10,000 steps a day a myth? How many steps you actually need URL: https://www.spiralstaircase.com/verdicts/you-need-10-000-steps-a-day Tested in a "What you've heard" box: Chapter 3, The Body That Walks (https://www.spiralstaircase.com/book/3-the-body-that-walks) Claim: You need 10,000 steps a day. Verdict: A round number, not a threshold. Evidence grade: Probable. Evidence: The number has no documented scientific origin, and the usual story of where it came from traces to no primary source. The pooled cohorts found most of the benefit below it, at a point that depends on your age. The curves flattened without turning back up, so more is fine if you enjoy it; falling short of the round number is not failure. ### Does a cold plunge after lifting hurt muscle growth? URL: https://www.spiralstaircase.com/verdicts/an-ice-bath-after-lifting-helps-you-recover Tested in a "What you've heard" box: Chapter 4, Load, Strength and Bone (https://www.spiralstaircase.com/book/4-load-strength-and-bone) Claim: An ice bath after lifting helps you recover. Verdict: Wrong if building muscle is the goal. Evidence grade: Probable. Evidence: For strength training, the evidence points the other way. In a three-month trial, active men lifted twice a week and then spent ten minutes either in cold water or doing light active recovery. Strength and muscle mass rose more with active recovery. The authors wrote that cold water as a regular recovery habit "should be reconsidered." Pooled analyses since agree in direction: regular cold immersion straight after lifting blunts muscle growth and, in most analyses, strength gains, while endurance gains seem unaffected. The effect is small to moderate, and clearest when only the trained limbs are cooled. No pooled analysis defines a safe gap, so the cautious reading is to take the plunge on days you do not lift, or hours apart (Chapter 9). Sources (note numbers of Chapter 4): - Roberts, L.A., Raastad, T., Markworth, J.F., Figueiredo, V.C., et al. (2015). "Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training." Journal of Physiology, 593(18), 4285-4301. https://doi.org/10.1113/JP270570; Malta, E.S., Dutra, Y.M., Broatch, J.R., Bishop, D.J., and Zagatto, A.M. (2021). "The effects of regular cold-water immersion use on training-induced changes in strength and endurance performance: a systematic review with meta-analysis." Sports Medicine, 51(1), 161-174. https://doi.org/10.1007/s40279-020-01362-0; Grgic, J. (2023). "Effects of post-exercise cold-water immersion on resistance training-induced gains in muscular strength: a meta-analysis." European Journal of Sport Science, 23(3), 372-380. https://doi.org/10.1080/17461391.2022.2033851; Piñero, A., Burke, R., Augustin, F., Mohan, A., et al. (2024). "Throwing cold water on muscle growth: a systematic review with meta-analysis of the effects of postexercise cold water immersion on resistance training-induced hypertrophy." European Journal of Sport Science, 24(2), 177-189. https://doi.org/10.1002/ejsc.12074 (Roberts: 21 men, 12 weeks; fast-twitch fibers grew only in the active-recovery group.) ### Is more protein always better? URL: https://www.spiralstaircase.com/verdicts/more-protein-is-always-better Tested in a "What you've heard" box: Chapter 4, Load, Strength and Bone (https://www.spiralstaircase.com/book/4-load-strength-and-bone) Claim: More protein is always better. Verdict: False. Past a point, extra protein stops adding muscle. Evidence grade: Strong. Evidence: In pooled trials, protein supplements added modestly to the strength and muscle that training builds. But the gains in lean mass stopped rising at about 1.6 grams per kilogram of body weight a day, or about three-quarters of a gram per pound. That figure is an estimate with a wide margin of error, so a few people may benefit from a little more, and the supplements helped less as age rose. Without training, extra protein made no meaningful difference to strength. Healthy kidneys handled higher-protein diets without measurable harm in mostly short trials, though four US professional societies, writing about people on weight-loss drugs, advise against staying above 2 grams per kilogram (about 0.9 grams per pound) for long, and people with serious kidney disease need their clinician's advice. Past the point the muscle can use, protein is just food. Sources (note numbers of Chapter 4): - Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., et al. (2018). "A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults." British Journal of Sports Medicine, 52(6), 376-384. https://doi.org/10.1136/bjsports-2017-097608; Tagawa, R., Watanabe, D., Ito, K., Otsuyama, T., et al. (2022). "Synergistic effect of increased total protein intake and strength training on muscle strength: a dose-response meta-analysis of randomized controlled trials." Sports Medicine - Open, 8(1), 110. https://doi.org/10.1186/s40798-022-00508-w; Devries, M.C., Sithamparapillai, A., Brimble, K.S., Banfield, L., et al. (2018). "Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis." Journal of Nutrition, 148(11), 1760-1775. https://doi.org/10.1093/jn/nxy197; Mozaffarian, D., Agarwal, M., Aggarwal, M., Alexander, L., et al. (2025). "Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society." American Journal of Clinical Nutrition, 122(1), 344-367. https://doi.org/10.1016/j.ajcnut.2025.04.023 (Morton: 49 trials; the break point is 1.62 g/kg a day, 95% CI 1.03-2.20. Devries: 28 trials on kidney function.) ### Should people without diabetes wear a glucose monitor? URL: https://www.spiralstaircase.com/verdicts/everyone-should-wear-a-glucose-monitor-to-find-their Tested in a "What you've heard" box: Chapter 5, Eat (https://www.spiralstaircase.com/book/5-eat) Claim: Everyone should wear a glucose monitor to find their spikes. Verdict: No evidence of benefit for people without diabetes. A curiosity, not a health tool, and no substitute for a blood test. Evidence grade: Emerging. Evidence: The first over-the-counter continuous glucose monitor was cleared by US regulators in 2024 for adults not using insulin, with a warning that users "should not make medical decisions based on the device's output without talking to their healthcare provider." The devices show something real: blood sugar rises after meals, sometimes well above its fasting level. That is normal physiology. Even healthy, slim people spend about half an hour a day above the top of the usual range, and older people with normal blood sugar about three hours. The monitor's estimate of average blood sugar can run high in healthy people, and the trials of glucose-monitor feedback were almost all in people with diabetes, with modest effects and frequent industry ties. Sources (note numbers of Chapter 5): - US Food and Drug Administration (2024). "FDA clears first over-the-counter continuous glucose monitor." Press announcement, 5 March 2024. https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor; Shah, V.N., DuBose, S.N., Li, Z., Beck, R.W., et al. (2019). "Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study." Journal of Clinical Endocrinology and Metabolism, 104(10), 4356-4364. https://doi.org/10.1210/jc.2018-02763; Spartano, N.L., Sultana, N., Lin, H., Cheng, H., et al. (2025). "Defining continuous glucose monitor time in range in a large, community-based cohort without diabetes." Journal of Clinical Endocrinology and Metabolism, 110(4), 1128-1134. https://doi.org/10.1210/clinem/dgae626 (time above 140 mg/dL; the community sample had a mean age of 58.5); Shah, V.N., Vigers, T., Pyle, L., Calhoun, P., and Bergenstal, R.M. (2023). "Discordance between glucose management indicator and glycated hemoglobin in people without diabetes." Diabetes Technology and Therapeutics, 25(5), 324-328. https://doi.org/10.1089/dia.2022.0544; Richardson, K.M., Jospe, M.R., Bohlen, L.C., Crawshaw, J., et al. (2024). "The efficacy of using continuous glucose monitoring as a behaviour change tool in populations with and without diabetes: a systematic review and meta-analysis of randomised controlled trials." International Journal of Behavioral Nutrition and Physical Activity, 21(1), 145. https://doi.org/10.1186/s12966-024-01692-6 (25 trials, none in healthy adults with normal blood sugar as a group; 11 had conflicts of interest tied to glucose monitors) ### Is 8 glasses of water a day a myth? URL: https://www.spiralstaircase.com/verdicts/drink-at-least-eight-glasses-of-water-a-day Tested in a "What you've heard" box: Chapter 5, Eat (https://www.spiralstaircase.com/book/5-eat) Claim: Drink at least eight glasses of water a day. Verdict: False as a rule. Drink to thirst, more in heat and hard exercise, and never past thirst in long events. Evidence grade: Probable. Evidence: The rule seems to have grown from a 1945 US allowance of about two and a half liters a day that came with two caveats: most of it was already in food, and "sensations of thirst usually serve as adequate guides to intake except for infants and sick persons." The allowance traveled; the caveats did not. A physiologist who went looking for the evidence summed up: "No scientific studies were found in support of 8 x 8." The US National Academies later concluded that most healthy people "adequately meet their daily hydration needs by letting thirst be their guide," and found no convincing evidence that caffeine dries you out. The rule can even do harm. At one Boston Marathon, about one runner in eight tested at the finish had too little sodium in their blood, most often those who drank so much that they gained weight during the race. Sources (note numbers of Chapter 5): - Food and Nutrition Board, National Research Council (1945). Recommended Dietary Allowances, Revised 1945. Reprint and Circular Series No. 122 (August 1945). Washington, DC. https://dspace.gipe.ac.in/xmlui/bitstream/handle/10973/36074/GIPE-031998.pdf; Valtin, H. (2002). "'Drink at least eight glasses of water a day.' Really? Is there scientific evidence for '8 x 8'?" American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 283(5), R993-R1004. https://doi.org/10.1152/ajpregu.00365.2002; National Academies (2004, 11 February). "Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk." https://www.nationalacademies.org/news/report-sets-dietary-intake-levels-for-water-salt-and-potassium-to-maintain-health-and-reduce-chronic-disease-risk; Almond, C.S., Shin, A.Y., Fortescue, E.B., Mannix, R.C., et al. (2005). "Hyponatremia among runners in the Boston Marathon." New England Journal of Medicine, 352(15), 1550-1556. https://doi.org/10.1056/NEJMoa043901 (488 runners gave blood at the finish; weight gain during the race went with about four times the odds of low sodium) (the 1945 text: "Most of this quantity is contained in prepared foods"; low sodium was also more common in slower runners) ### Do probiotic pills fix your gut? URL: https://www.spiralstaircase.com/verdicts/probiotic-pills-fix-your-gut Tested in a "What you've heard" box: Chapter 6, The Gut That Expects Dirt (https://www.spiralstaircase.com/book/6-the-gut-that-expects-dirt) Claim: Probiotic pills fix your gut. Verdict: For healthy people, unsupported; spend the money on yogurt and beans. Evidence grade: Probable. Evidence: In a review of seven randomized trials, probiotic supplements did not change the diversity of healthy adults' gut microbes compared with a placebo. In one small study, a probiotic taken after antibiotics even slowed the gut's recovery. Gastroenterologists back specific probiotics only for narrow uses, such as helping prevent the gut infection C. difficile during antibiotics. The clearest proof that gut microbes matter comes from the opposite direction: a donor-stool infusion, given after antibiotics and a bowel wash, cured about four in five patients with recurrent C. difficile in one trial. A capsule of a few strains is a different thing. Sources (note numbers of Chapter 6): - Kristensen, N.B., Bryrup, T., Allin, K.H., Nielsen, T., et al. (2016). "Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials." Genome Medicine, 8(1), 52. https://doi.org/10.1186/s13073-016-0300-5; Suez, J., Zmora, N., Zilberman-Schapira, G., Mor, U., et al. (2018). "Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT." Cell, 174(6), 1406-1423.e16. https://doi.org/10.1016/j.cell.2018.08.047; Su, G.L., Ko, C.W., Bercik, P., Falck-Ytter, Y., et al. (2020). "AGA clinical practice guidelines on the role of probiotics in the management of gastrointestinal disorders." Gastroenterology, 159(2), 697-705. https://doi.org/10.1053/j.gastro.2020.05.059; van Nood, E., Vrieze, A., Nieuwdorp, M., Fuentes, S., et al. (2013). "Duodenal infusion of donor feces for recurrent Clostridium difficile." New England Journal of Medicine, 368(5), 407-415. https://doi.org/10.1056/NEJMoa1205037 (donor stool after a short course of vancomycin and a bowel wash cured 13 of 16, against 4 of 13 on vancomycin alone) ### Can a greens powder replace vegetables? URL: https://www.spiralstaircase.com/verdicts/a-scoop-of-greens-powder-covers-your-vegetables Tested in a "What you've heard" box: Chapter 6, The Gut That Expects Dirt (https://www.spiralstaircase.com/book/6-the-gut-that-expects-dirt) Claim: A scoop of greens powder covers your vegetables. Verdict: Expensive vitamins, and no substitute for vegetables. Evidence grade: Emerging. Evidence: The best evidence is a systematic review of commercial mixed fruit and vegetable concentrates. They raised blood levels of beta-carotene, vitamins C and E and folate, and lowered some laboratory markers of oxidation, with no serious side effects. But the studies measured blood markers, not illness, the products varied widely, and there is no evidence that the powders improve outcomes such as heart disease. The fiber findings in this chapter, and the links to lower death rates, come from eating plants themselves. Sources (note numbers of Chapter 6): - Esfahani, A., Wong, J.M.W., Truan, J., Villa, C.R., et al. (2011). "Health effects of mixed fruit and vegetable concentrates: a systematic review of the clinical interventions." Journal of the American College of Nutrition, 30(5), 285-294. https://doi.org/10.1080/07315724.2011.10719971 (22 reports of commercial concentrates) ### Is leaky gut real? URL: https://www.spiralstaircase.com/verdicts/a-leaky-gut-is-behind-your-symptoms Tested in a "What you've heard" box: Chapter 6, The Gut That Expects Dirt (https://www.spiralstaircase.com/book/6-the-gut-that-expects-dirt) Claim: A "leaky gut" is behind your symptoms. Verdict: Real in specific diseases, unproven as an everyday diagnosis. Evidence grade: Emerging. Evidence: How easily things slip through the gut lining can be measured, and that leakiness does rise in celiac disease and inflammatory bowel disease, and with endurance exercise, pregnancy and anti-inflammatory painkillers. As sold online, though, "leaky gut" is a diagnosis without a reliable test: one widely used commercial blood kit for zonulin, a protein that helps regulate the seal between gut cells, does not detect zonulin. Sources (note numbers of Chapter 6): - Camilleri, M. (2019). "Leaky gut: mechanisms, measurement and clinical implications in humans." Gut, 68(8), 1516-1526. https://doi.org/10.1136/gutjnl-2019-318427 ; Scheffler, L., Crane, A., Heyne, H., Tönjes, A., et al. (2018). "Widely used commercial ELISA does not detect precursor of haptoglobin2, but recognizes properdin as a potential second member of the zonulin family." Frontiers in Endocrinology, 9, 22. https://doi.org/10.3389/fendo.2018.00022 ### Do blue light glasses work for sleep? URL: https://www.spiralstaircase.com/verdicts/blue-blocking-glasses-protect-your-sleep-from-screens Tested in a "What you've heard" box: Chapter 7, Light and Dark (https://www.spiralstaircase.com/book/7-light-and-dark) Claim: Blue-blocking glasses protect your sleep from screens. Verdict: Mostly unsupported; skip the glasses unless a clinician suggests them for a specific sleep problem. Evidence grade: Strong that the evidence for the glasses is weak. Evidence: A Cochrane review found that blue-filtering lenses may do nothing for eye strain from computer use, and could not say whether they help sleep, because the evidence was of very low certainty. Amber lenses showed mixed results, with a possible benefit in specific sleep or mood disorders. A National Sleep Foundation panel could not agree that the light from screens before bed harms sleep, and found that filtering blue light gave "only minimal improvements." Brightness and timing matter more than color, and dimming the room does the same job for nothing. Screens do disturb sleep in other ways, especially for children and teenagers (Chapter 12). Sources (note numbers of Chapter 7): - Singh, S., Keller, P.R., Busija, L., McMillan, P., et al. (2023). "Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults." Cochrane Database of Systematic Reviews, 8(8), CD013244. https://doi.org/10.1002/14651858.CD013244.pub2 (Seventeen trials.) ; Shechter, A., Quispe, K.A., Mizhquiri Barbecho, J.S., Slater, C., et al. (2020). "Interventions to reduce short-wavelength ('blue') light exposure at night and their effects on sleep: a systematic review and meta-analysis." Sleep Advances, 1(1), zpaa002. https://doi.org/10.1093/sleepadvances/zpaa002 ; Hartstein, L.E., Mathew, G.M., Reichenberger, D.A., Rodriguez, I., et al. (2024). "The impact of screen use on sleep health across the lifespan: A National Sleep Foundation consensus statement." Sleep Health, 10(4), 373-384. https://doi.org/10.1016/j.sleh.2024.05.001 ### Does ten minutes of morning sunlight set your body clock? URL: https://www.spiralstaircase.com/verdicts/ten-minutes-of-morning-sunlight-sets-your-body-clock Tested in a "What you've heard" box: Chapter 7, Light and Dark (https://www.spiralstaircase.com/book/7-light-and-dark) Claim: Ten minutes of morning sunlight sets your body clock for the day. Verdict: Right direction, invented number. Get outside early, and stay longer when it is gray. Evidence grade: Probable. Evidence: No study has tested ten minutes. The clock's response is steep at first and then flattens: in a laboratory study of evening light, twelve minutes of bright light produced about two-fifths of the shift that four hours did. Those volunteers had been kept in dim rooms beforehand, which makes the clock more sensitive, so the figures show the shape of the response, not a morning dose. Past moderate brightness, making light last longer helped more than making it brighter, and outdoor light, even in shade or under cloud, is many times brighter than a lit room. Sources (note numbers of Chapter 7): - Chang, A.M., Santhi, N., St Hilaire, M., Gronfier, C., et al. (2012). "Human responses to bright light of different durations." Journal of Physiology, 590(13), 3103-3112. https://doi.org/10.1113/jphysiol.2011.226555 (Evening light after a dim-light baseline; 12 minutes gave a 1.07-hour delay against 2.65 hours for 4 hours.) ; Dewan, K., Benloucif, S., Reid, K., Wolfe, L.F., et al. (2011). "Light-induced changes of the circadian clock of humans: increasing duration is more effective than increasing light intensity." Sleep, 34(5), 593-599. https://doi.org/10.1093/sleep/34.5.593 ### Should you wait 90 minutes after waking for coffee? URL: https://www.spiralstaircase.com/verdicts/wait-90-minutes-after-waking-before-your-first-coffee Tested in a "What you've heard" box: Chapter 8, Sleep (https://www.spiralstaircase.com/book/8-sleep) Claim: Wait 90 minutes after waking before your first coffee. Verdict: Untested, and the reasoning looks backward. Drink your coffee when you like it in the morning; the timing that matters is the hours before bed. Evidence grade: Emerging for any benefit of waiting. Evidence: The idea borrows real physiology. A brain chemical called adenosine helps build the pressure to sleep; the claim is that it needs time to clear after waking, and that coffee on top of the morning rise in cortisol, a stress hormone, sets up a crash. No trial has compared coffee at waking with coffee 90 minutes later. The mechanism also looks backward: in cats, adenosine rose during waking and fell during sleep, so it should be low after a night's rest, though no one has measured it in people just after waking. And in a controlled trial, after five days of regular caffeine the first morning dose no longer raised cortisol, though a later dose still did: daily use blunts the response rather than removing it. Sources (note numbers of Chapter 8): - Porkka-Heiskanen, T., Strecker, R.E., Thakkar, M., Bjorkum, A.A., et al. (1997). "Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness." Science, 276(5316), 1265-1268. https://doi.org/10.1126/science.276.5316.1265 ; Lovallo, W.R., Whitsett, T.L., al'Absi, M., Sung, B.H., et al. (2005). "Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels." Psychosomatic Medicine, 67(5), 734-739. https://doi.org/10.1097/01.psy.0000181270.20036.06 (After five days at 300 or 600 mg a day, a 9 a.m. dose no longer raised cortisol, but a 1 p.m. dose did; the authors conclude that responses are "reduced, but not eliminated" in daily users.) Adenosine data are from the basal forebrain of cats. ### Do tart cherry juice and magnesium help you sleep? URL: https://www.spiralstaircase.com/verdicts/tart-cherry-juice-and-magnesium-will-fix-your-sleep Tested in a "What you've heard" box: Chapter 8, Sleep (https://www.spiralstaircase.com/book/8-sleep) Claim: Tart cherry juice and magnesium will fix your sleep. Verdict: Unproven. The juice adds sugar, and magnesium is a long shot, not a treatment. Evidence grade: Emerging. Evidence: Tart cherries contain melatonin, but far less than a low-dose pill. The four trials were small and short: two found gains on some measures, one a modest effect on night waking, and the largest, which used capsules, found nothing. A recent review called the evidence limited. Magnesium has more trials and a similar story. A newer review of randomized trials rated the evidence low to very low certainty and did not support magnesium as a routine treatment for insomnia, though it may help a little in some people. Check with a clinician before taking magnesium if you have kidney disease or take other medicines. Sources (note numbers of Chapter 8): - Burkhardt, S., Tan, D.X., Manchester, L.C., Hardeland, R., et al. (2001). "Detection and quantification of the antioxidant melatonin in Montmorency and Balaton tart cherries (Prunus cerasus)." Journal of Agricultural and Food Chemistry, 49(10), 4898-4902. https://doi.org/10.1021/jf010321+ ; Barforoush, F., Ebrahimi, S., Abdar, M.K., Khademi, S., et al. (2025). "The effect of tart cherry on sleep quality and sleep disorders: a systematic review." Food Science & Nutrition, 13(9), e70923. https://doi.org/10.1002/fsn3.70923 ; Tucker, R.M., Kim, N., Gurzell, E., Mathi, S., et al. (2024). "Commonly used dose of Montmorency tart cherry powder does not improve sleep or inflammation outcomes in individuals with overweight or obesity." Nutrients, 16(23), 4125. https://doi.org/10.3390/nu16234125 ; Lopresti, A.L., Smith, S.J., and Drummond, P.D. (2026). "Magnesium supplementation for sleep in adults: a systematic review of randomized controlled trials." Journal of Dietary Supplements, 23(5), 553-581. https://doi.org/10.1080/19390211.2026.2719670 (12 randomized trials.) ; Pigeon, W.R., Carr, M., Gorman, C., and Perlis, M.L. (2010). "Effects of a tart cherry juice beverage on the sleep of older adults with insomnia: a pilot study." Journal of Medicinal Food, 13(3), 579-583. https://doi.org/10.1089/jmf.2009.0096 ; Howatson, G., Bell, P.G., Tallent, J., Middleton, B., et al. (2012). "Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality." European Journal of Nutrition, 51(8), 909-916. https://doi.org/10.1007/s00394-011-0263-7 ; Losso, J.N., Finley, J.W., Karki, N., Liu, A.G., et al. (2018). "Pilot study of the tart cherry juice for the treatment of insomnia and investigation of mechanisms." American Journal of Therapeutics, 25(2), e194-e201. https://doi.org/10.1097/MJT.0000000000000584 (Each tart cherry trial had at most a few dozen participants and lasted a week or two.) ### Can NSDR or yoga nidra replace lost sleep? URL: https://www.spiralstaircase.com/verdicts/nsdr-or-yoga-nidra-can-stand-in-for-lost-sleep Tested in a "What you've heard" box: Chapter 8, Sleep (https://www.spiralstaircase.com/book/8-sleep) Claim: NSDR or yoga nidra can stand in for lost sleep. Verdict: A pleasant way to rest, not a substitute for sleep. Evidence grade: Emerging for small benefits. Evidence: Guided rest practices such as yoga nidra, and the related practice sold as non-sleep deep rest, do relax people. In the largest online trial the gains in well-being were very small, and a recent review of yoga nidra for insomnia rated the evidence very low certainty. Nothing shows that any practice replaces sleep. Sources (note numbers of Chapter 8): - Moszeik, E.N., Rohleder, N., and Renner, K.H. (2025). "The effects of an online Yoga Nidra meditation on subjective well-being and diurnal salivary cortisol: a randomised controlled trial." Stress and Health, 41(3), e70049. https://doi.org/10.1002/smi.70049 (Several hundred adults over two months.) ; Singh, S., Dhanlika, D., Singh, U., Haldar, P., and Sharma, G. (2026). "Effect of yoga Nidra (yogic sleep) in sleep disturbances and insomnia: systematic review and metanalysis." Sleep and Breathing, 30(2), 144. https://doi.org/10.1007/s11325-026-03685-0 (Effect sizes d = 0.08 to 0.16.) ### Does a cold plunge burn fat? Brown fat, sized honestly URL: https://www.spiralstaircase.com/verdicts/brown-fat-will-make-you-lean Tested in a "What you've heard" box: Chapter 9, Heat and Cold (https://www.spiralstaircase.com/book/9-heat-and-cold) Claim: Brown fat will make you lean. Verdict: Oversold. Mild cold may nudge insulin sensitivity in tiny trials, but it will not move your weight. Evidence grade: Probable that the claim is oversold; Emerging for the insulin effect. Evidence: Brown fat does switch on in the cold, and a few weeks of regular mild cold can grow it. But its output, measured directly in one oxygen-tracer study, came to roughly 15 to 25 calories a day in mild cold, even in people with large deposits. The "hundreds of calories a day" figures that circulate come from a heat-production rate measured while people sat in the cold, stretched over a whole day. When small studies, mostly of single cold sessions, were pooled, fasting blood sugar, insulin and triglycerides did not change. Among tens of thousands of patients scanned for cancer care, those with visible brown fat had about half the rate of the common adult form of diabetes, but a single snapshot cannot show which came first. Sources (note numbers of Chapter 9): - Muzik, O., Mangner, T.J., Leonard, W.R., Kumar, A., et al. (2013). "15O PET measurement of blood flow and oxygen consumption in cold-activated human brown fat." Journal of Nuclear Medicine, 54(4), 523-531. https://doi.org/10.2967/jnumed.112.111336 ; Tabei, S., Chamorro, R., Meyhöfer, S.M., and Wilms, B. (2024). "Metabolic effects of brown adipose tissue activity due to cold exposure in humans: a systematic review and meta-analysis of RCTs and non-RCTs." Biomedicines, 12(3), 537. https://doi.org/10.3390/biomedicines12030537 (7 studies, 85 participants, mostly acute exposures; only free fatty acids rose); Becher, T., Palanisamy, S., Kramer, D.J., Eljalby, M., et al. (2021). "Brown adipose tissue is associated with cardiometabolic health." Nature Medicine, 27(1), 58-65. https://doi.org/10.1038/s41591-020-1126-7 (52,487 patients having PET/CT, mostly for cancer care, scans not cold-stimulated; type 2 diabetes 4.6% with detectable brown fat versus 9.5% without); Yoneshiro et al. (2013), as note 11 (cold-induced heat production of 108 to 289 kcal/day is a rate measured during 2 hours of cold, not a daily burn) ### Does a cold plunge raise dopamine 250%? The study behind the number URL: https://www.spiralstaircase.com/verdicts/cold-water-raises-dopamine-by-250 Tested in a "What you've heard" box: Chapter 9, Heat and Cold (https://www.spiralstaircase.com/book/9-heat-and-cold) Claim: Cold water raises dopamine by 250%. Verdict: A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose. Evidence grade: Emerging. Evidence: The figure comes from a laboratory study of young men who sat neck-deep in water at 57°F for a full hour, and the dopamine measured in their blood rose by the quoted amount. Blood dopamine is not brain dopamine, the study measured nothing about mood or motivation, and an hour at that temperature bears no resemblance to a two-minute plunge. The pooled trials of cold-water immersion found no effect on mood. Sources (note numbers of Chapter 9): - Srámek, P., Simecková, M., Janský, L., Savlíková, J., and Vybíral, S. (2000). "Human physiological responses to immersion into water of different temperatures." European Journal of Applied Physiology, 81(5), 436-442. https://doi.org/10.1007/s004210050065 (one hour of head-out immersion at 14°C; metabolic rate rose about 350% and plasma dopamine 250%; mood was not measured) ### Is 11 minutes of cold and 57 of heat a week optimal? URL: https://www.spiralstaircase.com/verdicts/eleven-minutes-of-cold-and-fifty-seven-minutes-of-heat Tested in a "What you've heard" box: Chapter 9, Heat and Cold (https://www.spiralstaircase.com/book/9-heat-and-cold) Claim: Eleven minutes of cold and fifty-seven minutes of heat a week is the optimal protocol. Verdict: Not a protocol. Evidence grade: Emerging. Evidence: Nobody tested it. The numbers come from a small Danish study comparing a handful of young men who swam in winter water and used a sauna with men who did not. Those figures were the swimmers' own weekly averages. They made more heat in the cold, but their brown fat responded no more strongly than the controls', and the authors warned that so small a sample could mislead in either direction. It is a description of what a few volunteers already did, measured once. Sources (note numbers of Chapter 9): - Søberg, S., Löfgren, J., Philipsen, F.E., Jensen, M., et al. (2021). "Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men." Cell Reports Medicine, 2(10), 100408. https://doi.org/10.1016/j.xcrm.2021.100408 (8 swimmers and 8 controls, one swimmer excluded; the weekly means are self-reported by seven swimmers) ### Does forest bathing work through tree chemicals? URL: https://www.spiralstaircase.com/verdicts/forest-bathing-works-because-trees-release-chemicals Tested in a "What you've heard" box: Chapter 10, Green and Quiet (https://www.spiralstaircase.com/book/10-green-and-quiet) Claim: Forest bathing works because trees release chemicals, called phytoncides, that boost your immune system and fight cancer. Verdict: Enjoy the forest as relaxation, plausible though the size is uncertain; the tree-chemical immune story is unproven. Evidence grade: Emerging for both. Evidence: The chemical story traces to one Japanese laboratory. Its best-known test put a dozen men in a Tokyo hotel room for three nights with cypress oil vaporized in the air, and found their immune killer cells more active than on a normal working day. There was no placebo scent, nobody was blinded, and a hotel stay is itself a break from work. The laboratory's leader sits on forest-therapy boards. Killer-cell activity is only a stand-in, and no cancer outcome was ever measured. Even for short-term effects on the heart and mood, a recent pooled analysis rated the certainty of the evidence "very low." Forests may still help people relax for a while: pooled small trials suggest blood pressure runs a little lower on the same day. The likeliest reasons are ordinary ones: shade, quiet, walking and company. Sources (note numbers of Chapter 10): - Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., et al. (2009). "Effect of phytoncide from trees on human natural killer cell function." International Journal of Immunopathology and Pharmacology, 22(4), 951-959. https://doi.org/10.1177/039463200902200410 (12 men, three nights, hinoki cypress oil.) ; Li, Q. (2022). "Effects of forest environment (Shinrin-yoku/Forest bathing) on health promotion and disease prevention: the establishment of 'Forest Medicine'." Environmental Health and Preventive Medicine, 27, 43. https://doi.org/10.1265/ehpm.22-00160 (board memberships declared) ; Andrade, A.M., Durães, S.D.F., Franco Netto, L.C.R., Fenner, A.L.D., et al. (2026). "Short-term cardiovascular and mental health responses to Shinrin-Yoku (forest bathing): a systematic review and meta-analysis." Frontiers in Psychology, 17, 1707829. https://doi.org/10.3389/fpsyg.2026.1707829 (Published 2026.) ; Ideno, Y., Hayashi, K., Abe, Y., Ueda, K., et al. (2017). "Blood pressure-lowering effect of Shinrin-yoku (forest bathing): a systematic review and meta-analysis." BMC Complementary and Alternative Medicine, 17(1), 409. https://doi.org/10.1186/s12906-017-1912-z ; Markevych, I., Schoierer, J., Hartig, T., Chudnovsky, A., et al. (2017). "Exploring pathways linking greenspace to health: theoretical and methodological guidance." Environmental Research, 158, 301-317. https://doi.org/10.1016/j.envres.2017.06.028 ### Does a digital detox reset your brain? URL: https://www.spiralstaircase.com/verdicts/a-digital-detox-resets-your-brain Tested in a "What you've heard" box: Chapter 12, Attention in the Age of the Phone (https://www.spiralstaircase.com/book/12-attention-in-the-age-of-the-phone) Claim: A digital detox resets your brain. Verdict: A planned break brings a small lift and can reset a habit; "resets your brain" is overstated. Evidence grade: Probable. Evidence: The best trial, the four weeks off Facebook, found a small lift in well-being and a lasting drop in use. A systematic review of breaks from phones or social media found effects that "varied across studies": some helped, and others found no effect or even made well-being worse. A 2025 pooled analysis of randomized trials found a small benefit that varied with culture and with the length of the break. A widely reported one-week detox among American young adults found large drops in anxiety and depression, but the detox was optional and there was no comparison group, so those numbers cannot be read as its effect. Nothing here resets a brain, and the story that you can drain your dopamine and refill it is taken apart in Chapter 14. Sources (note numbers of Chapter 12): - Radtke, T., Apel, T., Schenkel, K., Keller, J., and von Lindern, E. (2022). "Digital detox: an effective solution in the smartphone era? A systematic literature review." Mobile Media & Communication, 10(2), 190-215. https://doi.org/10.1177/20501579211028647 ; Liu, Y., Mohamad, E.M.W., Azlan, A.A., and Tan, Y. (2025). "Am I happier without you? Social media detox and well-being: a meta-analysis of randomized controlled trials." Behavioral Sciences, 15(3), 290. https://doi.org/10.3390/bs15030290 ; Calvert, E., Cipriani, M., Dwyer, B., Lisowski, V., et al. (2025). "Social media detox and youth mental health." JAMA Network Open, 8(11), e2545245. https://doi.org/10.1001/jamanetworkopen.2025.45245 (The systematic review covered 21 studies; the 2025 detox study was an uncontrolled cohort.) ### Is screen time destroying a generation? URL: https://www.spiralstaircase.com/verdicts/screen-time-is-destroying-a-generation Tested in a "What you've heard" box: Chapter 12, Attention in the Age of the Phone (https://www.spiralstaircase.com/book/12-attention-in-the-age-of-the-phone) Claim: Screen time is destroying a generation. Verdict: Unproven as stated, with a serious case on both sides; heavy use is a fair worry, and the causal claim is open. Evidence grade: Emerging. Evidence: The rise in teenage depression, anxiety and self-harm is real and well documented. One prominent social psychologist argues that between about 2010 and 2015 a play-based childhood gave way to a phone-based one, that this is a major cause, and that girls were hit hardest; his remedies are later smartphones, phone-free schools and more free play. A developmental psychologist answered that searches for large effects have found only no, small and mixed associations, mostly correlational, and that where links appear over time, distressed young people seem to use the platforms more, rather than the platforms causing the distress. Across hundreds of thousands of adolescents, technology use accounted for a tiny slice of the differences in how teenagers felt, less than half of one percent. A later analysis found little overall sign that the link had grown stronger, though social media use had become more strongly tied to emotional problems. Heavier use keeps turning up alongside worse outcomes. Sources (note numbers of Chapter 12): - Odgers, C.L. (2024). "The great rewiring: is social media really behind an epidemic of teenage mental illness?" Nature, 628(8006), 29-30. https://doi.org/10.1038/d41586-024-00902-2 ; Twenge, J.M., Martin, G.N., and Campbell, W.K. (2018). "Decreases in psychological well-being among American adolescents after 2012 and links to screen time during the rise of smartphone technology." Emotion, 18(6), 765-780. (Twenge's analysis reports a cross-sectional dose-response link.) - Orben, A., and Przybylski, A.K. (2019). "The association between adolescent well-being and digital technology use." Nature Human Behaviour, 3(2), 173-182. https://doi.org/10.1038/s41562-018-0506-1 ; Vuorre, M., Orben, A., and Przybylski, A.K. (2021). "There is no evidence that associations between adolescents' digital technology engagement and mental health problems have increased." Clinical Psychological Science, 9(5), 823-835. https://doi.org/10.1177/2167702621994549 (Orben and Przybylski analyzed 355,358 adolescents across three datasets.) ### Is adrenal fatigue real? URL: https://www.spiralstaircase.com/verdicts/chronic-stress-wears-out-your-adrenal-glands-a Tested in a "What you've heard" box: Chapter 13, Stress and the Mind (https://www.spiralstaircase.com/book/13-stress-and-the-mind) Claim: Chronic stress wears out your adrenal glands, a condition called adrenal fatigue, and saliva tests and adrenal supplements can fix it. Verdict: False. If you are exhausted, see a clinician rather than the supplement aisle. Evidence grade: Probable. Evidence: A systematic review found "no substantiation that 'adrenal fatigue' is an actual medical condition," and concluded that it "is still a myth." The Endocrine Society says no test can detect it, and warns that adrenal hormone supplements taken without need can stop your own glands making the hormones you need under physical stress, risking a life-threatening crisis when the pills stop. What is real: a flattened daily cortisol rhythm, weakly linked to poorer health, and true adrenal failure (Addison's disease), a separate illness that doctors can test for. Sources (note numbers of Chapter 13): - Cadegiani, F.A., and Kater, C.E. (2016). "Adrenal fatigue does not exist: a systematic review." BMC Endocrine Disorders, 16(1), 48. https://doi.org/10.1186/s12902-016-0128-4 (58 studies.) ; Endocrine Society (2022). "Adrenal Fatigue." https://www.endocrine.org/patient-engagement/endocrine-library/adrenal-fatigue (Page last updated 25 January 2022; read September 2026.) ### The physiological sigh: what the evidence shows URL: https://www.spiralstaircase.com/verdicts/the-physiological-sigh-two-inhales-through-the-nose-and Tested in a "What you've heard" box: Chapter 13, Stress and the Mind (https://www.spiralstaircase.com/book/13-stress-and-the-mind) Claim: The physiological sigh, two inhales through the nose and a long exhale through the mouth, is the fastest proven way to calm down. Verdict: A reasonable quick reset with thin evidence; "fastest" and "proven" are overstated. Evidence grade: Emerging. Evidence: The claim rests on one trial. It randomly assigned about a hundred people, mostly undergraduates, to five minutes a day of mindfulness meditation or one of three breathing drills for four weeks. Every group felt better. Cyclic sighing lifted positive mood and slowed resting breathing more than meditation did, but anxiety fell equally in all groups, and nobody's heart-rate variability changed. The authors describe it as exploratory and registered it retrospectively, and its instructional videos were recorded by one of them. Sources (note numbers of Chapter 13): - Balban, M.Y., Neri, E., Kogon, M.M., Weed, L., et al. (2023). "Brief structured respiration practices enhance mood and reduce physiological arousal." Cell Reports Medicine, 4(1), 100895. https://doi.org/10.1016/j.xcrm.2022.100895 (108 participants, mostly undergraduates; run June to September 2020 and registered retrospectively in March 2022, NCT05304000; instructional videos pre-recorded by one of the authors.) ### Can breathwork fix anxiety? URL: https://www.spiralstaircase.com/verdicts/breathwork-will-fix-your-anxiety Tested in a "What you've heard" box: Chapter 13, Stress and the Mind (https://www.spiralstaircase.com/book/13-stress-and-the-mind) Claim: Breathwork will fix your anxiety. Verdict: Helps a little; not a substitute for therapy or medication. Evidence grade: Probable. Evidence: Pooled across randomized trials, breathwork brought small-to-moderate reductions in stress, anxiety and depressive symptoms; most trials carried a moderate risk of bias, and the authors warned against "a miscalibration between hype and evidence." The fast-breathing and breath-hold styles popular online also carry a real hazard: they can cause fainting, and fainting in water can kill (see Safety below). An anxiety disorder is a treatable illness, and breathing belongs alongside its treatment. Sources (note numbers of Chapter 13): - Fincham, G.W., Strauss, C., Montero-Marin, J., and Cavanagh, K. (2023). "Effect of breathwork on stress and mental health: a meta-analysis of randomised-controlled trials." Scientific Reports, 13(1), 432. https://doi.org/10.1038/s41598-022-27247-y (12 trials and 785 adults for stress, effect -0.35; anxiety -0.32; depressive symptoms -0.40.) ### Does a dopamine detox actually work? URL: https://www.spiralstaircase.com/verdicts/a-dopamine-fast-resets-your-brain Tested in a "What you've heard" box: Chapter 14, Wanting, Loving, Losing, Meaning (https://www.spiralstaircase.com/book/14-wanting-loving-losing-meaning) Claim: A dopamine fast resets your brain. Verdict: The name misreads the science, and the behavior can help. Take a month off something that has stopped feeling like a choice, and skip the day-long fasts. Evidence grade: Emerging. Evidence: The idea is that a day or more without pleasures, such as phones, treats and music, lets your dopamine "reset". Dopamine is not a tank that drains and refills; it is a learning and wanting signal that responds to surprising rewards and the cues that predict them. A recent review of dopamine fasting reports no trials. One addiction psychiatrist advises thirty days away from a substance or behavior that has become compulsive, and that is clinical advice, not a trial result. A deliberate break can still help, because it interrupts the cue-and-habit loop and shows you what the habit was doing for you. Sources (note numbers of Chapter 14): - Desai, D., Patel, J., Saiyed, F., Upadhyay, H., et al. (2024). "A literature review on holistic well-being and dopamine fasting: an integrated approach." Cureus, 16(6), e61643. https://doi.org/10.7759/cureus.61643 ; Lembke, A. (2021). Dopamine Nation: Finding Balance in the Age of Indulgence. Dutton. (30 days of abstinence from a compulsively used substance or behavior.) ### Did Rat Park prove addiction is about the cage? URL: https://www.spiralstaircase.com/verdicts/rat-park-proved-addiction-is-about-the-cage-not-the-drug Tested in a "What you've heard" box: Chapter 14, Wanting, Loving, Losing, Meaning (https://www.spiralstaircase.com/book/14-wanting-loving-losing-meaning) Claim: Rat Park proved addiction is about the cage, not the drug. Verdict: Overstated. Environment matters a great deal, as the Vietnam veterans show, but the cage is not the whole story: drugs are rewarding in any cage. Evidence grade: Emerging for Rat Park itself; Probable for the wider principle. Evidence: In the late 1970s the psychologist Bruce Alexander housed some rats alone in standard cages and others together in a large, open "Rat Park", and gave them morphine solution to drink. The isolated rats drank more, and the story has been retold as proof that addiction is purely a product of a poor environment. The studies were tiny and measured drinking differently in the two settings, the Rat Park rats did drink morphine, and the original papers drew no lessons for humans. A later attempt to repeat the key result failed, and heroin and cocaine proved rewarding to rats whether housed alone or in groups. Better-designed work has since shown that, given a choice between a drug and contact with another rat, most rats chose the contact. Sources (note numbers of Chapter 14): - Alexander, B.K., Coambs, R.B., and Hadaway, P.F. (1978). "The effect of housing and gender on morphine self-administration in rats." Psychopharmacology, 58(2), 175-179. https://doi.org/10.1007/bf00426903 ; Gage, S.H., and Sumnall, H.R. (2019). "Rat Park: how a rat paradise changed the narrative of addiction." Addiction, 114(5), 917-922. https://doi.org/10.1111/add.14481 ; Petrie, B.F. (1996). "Environment is not the most important variable in determining oral morphine consumption in Wistar rats." Psychological Reports, 78(2), 391-400. https://doi.org/10.2466/pr0.1996.78.2.391 ; Bozarth, M.A., Murray, A., and Wise, R.A. (1989). "Influence of housing conditions on the acquisition of intravenous heroin and cocaine self-administration in rats." Pharmacology Biochemistry and Behavior, 33(4), 903-907. https://doi.org/10.1016/0091-3057(89)90490-5 ; Venniro, M., Zhang, M., Caprioli, D., Hoots, J.K., et al. (2018). "Volitional social interaction prevents drug addiction in rat models." Nature Neuroscience, 21(11), 1520-1529. https://doi.org/10.1038/s41593-018-0246-6 (the first Rat Park study used 32 rats, and intake was measured by weighing bottles in cages but counting drops in the park.) ### Does cycle syncing your workouts work? URL: https://www.spiralstaircase.com/verdicts/sync-your-workouts-to-your-cycle-lift-heavy-in-the Tested in a "What you've heard" box: Chapter 15, Women's Bodies Across the Life Course (https://www.spiralstaircase.com/book/15-womens-bodies-across-the-life-course) Claim: Sync your workouts to your cycle: lift heavy in the first half, go easy in the second. Verdict: Not supported. Train consistently and adjust on days you feel bad, whatever the reason. Evidence grade: Probable. Evidence: The idea turns a real fact, that hormones swing across the cycle, into a training plan. The largest meta-analysis found at most a trivial dip in performance around menstruation, rated the evidence low quality, and concluded that general guidelines "cannot be formed." An umbrella review judged it "premature" to say that hormone swings meaningfully change strength or muscle growth. A small randomized study with hormone-confirmed phases found that muscle built protein at the same rate after lifting in either half of the cycle. Sources (note numbers of Chapter 15): - McNulty, K.L., Elliott-Sale, K.J., Dolan, E., Swinton, P.A., et al. (2020). "The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis." Sports Medicine, 50(10), 1813-1827. https://doi.org/10.1007/s40279-020-01319-3 ; Colenso-Semple, L.M., D'Souza, A.C., Elliott-Sale, K.J., and Phillips, S.M. (2023). "Current evidence shows no influence of women's menstrual cycle phase on acute strength performance or adaptations to resistance exercise training." Frontiers in Sports and Active Living, 5, 1054542. https://doi.org/10.3389/fspor.2023.1054542 ; Colenso-Semple, L.M., McKendry, J., Lim, C., Atherton, P.J., et al. (2025). "Menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar proteolysis in response to resistance exercise." Journal of Physiology, 603(5), 1109-1121. https://doi.org/10.1113/JP287342 (The 2025 crossover trial enrolled 12 women.; McNulty et al. pooled 78 studies) ### Does hormone therapy cause breast cancer? URL: https://www.spiralstaircase.com/verdicts/hormone-therapy-causes-breast-cancer Tested in a "What you've heard" box: Chapter 15, Women's Bodies Across the Life Course (https://www.spiralstaircase.com/book/15-womens-bodies-across-the-life-course) Claim: Hormone therapy causes breast cancer. Verdict: Partly true and badly overstated. The risk is real, modest and depends on type and duration. It argues for a careful choice of treatment; it does not argue for refusing one. Evidence grade: Strong for the trial figures; Probable for the pooled observational ones. Evidence: The type matters more than the headline. In the Women's Health Initiative, combined estrogen and progestin raised breast cancer modestly, while estrogen alone went the other way: fewer breast cancers and fewer breast cancer deaths over two decades of follow-up. The largest pooled analysis of observational data gives the size of the risk. Of 1,000 women who take hormones for five years from age fifty, it estimates about 20 extra breast cancers on estrogen plus a daily progestogen, about 14 when the progestogen is taken part of each month, and about 5 on estrogen alone. Ten years roughly doubles these. Vaginal estrogen showed no excess, and some of the excess lasted years after stopping. Sources (note numbers of Chapter 15): - Chlebowski, R.T., Anderson, G.L., Aragaki, A.K., Manson, J.E., et al. (2020). "Association of menopausal hormone therapy with breast cancer incidence and mortality during long-term follow-up of the Women's Health Initiative randomized clinical trials." JAMA, 324(4), 369-380. https://doi.org/10.1001/jama.2020.9482 ; Collaborative Group on Hormonal Factors in Breast Cancer (2019). "Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence." The Lancet, 394(10204), 1159-1168. https://doi.org/10.1016/S0140-6736(19)31709-X ; Manson et al. (2017), as above, for cancer mortality. (WHI combined therapy: about 0.45% vs 0.36% a year; the per-1,000 conversion is this book's arithmetic, and the pooled figures assume the association is causal, as the authors state.) ### Should men take testosterone after 40? URL: https://www.spiralstaircase.com/verdicts/every-man-over-forty-should-be-on-testosterone Tested in a "What you've heard" box: Chapter 16, Aging Well (https://www.spiralstaircase.com/book/16-aging-well) Claim: Every man over forty should be on testosterone. Verdict: False. Evidence grade: Strong. Evidence: Levels drift down slowly, and partly with weight and health, and only a minority of men meet the diagnosis of symptoms plus repeated low tests. In trials the benefits are modest and mostly sexual: more desire and activity, a little more energy, corrected anemia. The costs are real: switched-off sperm production, thicker blood, higher blood pressure, irregular heartbeat, clots in the lungs and more fractures. The US label still limits its use for age-related decline, and the Endocrine Society has warned against treating normal aging as disease. Test properly, fix weight first, and treat a confirmed deficiency with a clinician who will monitor you. Sources (note numbers of Chapter 16): - Lincoff et al. 2023 and US Food and Drug Administration 2025 (note 19); Snyder et al. 2024 (note 20); Endocrine Society 2026 (note 18); Fernández-Balsells et al. 2010 (note 40). ### Can an epigenetic age test tell you how fast you are aging? URL: https://www.spiralstaircase.com/verdicts/an-epigenetic-age-test-tells-you-how-fast-you-are-aging Tested in a "What you've heard" box: Chapter 16, Aging Well (https://www.spiralstaircase.com/book/16-aging-well) Claim: An epigenetic age test tells you how fast you are aging. Verdict: Not reliable for individuals. Evidence grade: Probable. Evidence: Cells tag their DNA with small chemical marks, and the tags at a few hundred sites predict a person's age across almost every tissue. These "clocks" work well for comparing large groups. For one person, they wobble: run the same sample twice and standard clocks could disagree by up to nine years from technical noise alone. In a two-year calorie-restriction trial, the best human evidence that a clock can be moved on purpose, one clock of three slowed slightly and the other two did not move. The best-known number about telomeres, the protective caps on chromosomes, has the same problem: the claim that stress added nine to seventeen years of cellular aging was an extrapolation from mothers measured once each. A test that cannot agree with itself cannot tell you whether last month's habits worked. Sources (note numbers of Chapter 16): - Horvath, S. (2013). "DNA methylation age of human tissues and cell types." Genome Biology, 14(10), R115. https://doi.org/10.1186/gb-2013-14-10-r115; Higgins-Chen, A.T., Thrush, K.L., Wang, Y., Minteer, C.J., et al. (2022). "A computational solution for bolstering reliability of epigenetic clocks: implications for clinical trials and longitudinal tracking." Nature Aging, 2(7), 644-661. https://doi.org/10.1038/s43587-022-00248-2; Waziry, R., Ryan, C.P., Corcoran, D.L., Huffman, K.M., et al. (2023). "Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial." Nature Aging, 3(3), 248-257. https://doi.org/10.1038/s43587-022-00357-y; Epel, E.S., Blackburn, E.H., Lin, J., Dhabhar, F.S., et al. (2004). "Accelerated telomere shortening in response to life stress." Proceedings of the National Academy of Sciences, 101(49), 17312-17315. https://doi.org/10.1073/pnas.0407162101 (CALERIE: DunedinPACE slowed about 2-3%, PhenoAge and GrimAge unchanged.) ### Do NAD+ supplements work? URL: https://www.spiralstaircase.com/verdicts/nad-boosters-and-other-longevity-supplements-slow-aging Tested in a "What you've heard" box: Chapter 16, Aging Well (https://www.spiralstaircase.com/book/16-aging-well) Claim: NAD+ boosters and other longevity supplements slow aging. Verdict: Unsupported so far. Evidence grade: Probable. Evidence: Supplements called NR and NMN reliably raise blood levels of NAD+, a molecule cells use to handle energy. The trouble is what happens next. One pooled analysis of the small NMN trials found blood levels rising but "most of the clinically relevant outcomes were not significantly different," and others found no clear gain in blood sugar, cholesterol, muscle or walking speed, and perhaps a small drop in the lower blood pressure number. No human trial has measured lifespan or age-related disease. Senolytics, drugs meant to clear worn-out cells, are further from the shelf than their marketing suggests: the first human test gave dasatinib, a leukemia drug, with quercetin, a supplement-aisle compound, to a handful of people for three days, with no comparison group, and counted cells rather than health. Dasatinib has real toxicity. That is not a supplement decision. Sources (note numbers of Chapter 16): - Martens, C.R., Denman, B.A., Mazzo, M.R., Armstrong, M.L., et al. (2018). "Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults." Nature Communications, 9(1), 1286. https://doi.org/10.1038/s41467-018-03421-7; Zhang, J., Poon, E.T., and Wong, S.H. (2025). "Efficacy of oral nicotinamide mononucleotide supplementation on glucose and lipid metabolism for adults: a systematic review with meta-analysis on randomized controlled trials." Critical Reviews in Food Science and Nutrition, 65(22), 4382-4400. https://doi.org/10.1080/10408398.2024.2387324; Prokopidis, K., Moriarty, F., Bahat, G., McLean, J., et al. (2025). "The effect of nicotinamide mononucleotide and riboside on skeletal muscle mass and function: a systematic review and meta-analysis." Journal of Cachexia, Sarcopenia and Muscle, 16(3), e13799. https://doi.org/10.1002/jcsm.13799; Chen, F., Zhou, D., Kong, A.P., Yim, N.T., et al. (2024). "Effects of nicotinamide mononucleotide on glucose and lipid metabolism in adults: a systematic review and meta-analysis of randomised controlled trials." Current Diabetes Reports, 25(1), 4. https://doi.org/10.1007/s11892-024-01557-z; Zhang, M., Chen, Y., Jiang, N., Zeng, J., et al. (2026). "Effects of nicotinamide mononucleotide supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials." Nutrients, 18(6), 890. https://doi.org/10.3390/nu18060890; Hickson, L.J., Langhi Prata, L.G.P., Bobart, S.A., Evans, T.K., et al. (2019). "Senolytics decrease senescent cells in humans: preliminary report from a clinical trial of Dasatinib plus Quercetin in individuals with diabetic kidney disease." EBioMedicine, 47, 446-456. https://doi.org/10.1016/j.ebiom.2019.08.069 (Zhang 2025 pooled 12 studies and 513 people; the senolytic study treated nine people.) ## The book, chapter by chapter ### Chapter 1: The Short Version URL: https://www.spiralstaircase.com/book/1-the-short-version Start here: - If you smoke, quit with help (strong). How: ask a doctor, pharmacist or quitline for varenicline or combination nicotine replacement (a patch plus gum, lozenges or spray), or switch completely to a regulated nicotine e-cigarette as a stepping-stone off cigarettes. Keep the break, change the place: if cigarettes come with company, take breaks where nobody smokes. Why: nothing else in this book moves your odds as far. - Walk more than you do now, toward seven or eight thousand steps a day (strong, probable). You do not need 10,000. How: add one twenty-minute walk a day, about two thousand brisk steps; brisk means about a hundred steps a minute, so count your steps for fifteen seconds and aim for twenty-five. Make it a default: walk to something, on a fixed route, at a fixed time. Build up over weeks; sore feet and shins are the usual price of a sudden jump. Why: the steepest part of the curve is at the bottom. - Lift twice a week, about half an hour each time (strong, probable). How: four or five moves that work the major muscle groups with what you have: sit-to-stands from a chair, push-ups against a wall or counter, rows with a band or a loaded backpack, carrying shopping bags. Do two or three rounds of each, stopping each set while a couple more good repetitions would still be possible; you need not push to failure. Add repetitions first, then load. Why: in the trials behind the guidance, training beat no training for strength and everyday function. - Swap the ultra-processed meals you eat most often (probable). How: pick the two or three meals you repeat most, such as breakfast and a work lunch, and rebuild them from ingredients: oats and fruit instead of a packaged bar, beans, eggs or leftovers instead of a vending-machine lunch. Keep the swaps boring and repeatable. Why: in a controlled trial, the same people ate about five hundred calories a day more when the food was ultra-processed. ### Chapter 2: What Your Body Expects, and How to Trust This Book URL: https://www.spiralstaircase.com/book/2-what-your-body-expects-and-how-to-trust-this-book Start here: - Settle the dairy question with a two-week trial, not a DNA kit (probable). How: if milk reliably brings bloating, gas or cramps, switch to lactose-free dairy, or take a lactase enzyme with dairy, for two weeks. Then drink ordinary milk again on purpose and see what happens. Fermented dairy such as yogurt is often fine when milk is not. Why: losing lactase after childhood is the normal state for most adults on earth. Persistent gut symptoms still deserve a doctor, since celiac disease and inflammatory bowel disease can imitate lactose trouble. - Check one thing you already pay for (a habit, not a treatment). How: pick the supplement, powder or program you spend the most on. Find the study it rests on and ask the five questions above. If you cannot find a study, or it measured something else, stop buying it for a month. Why: the claims in the table above failed exactly this check. - If a drink turns your face red, whatever your background, treat it as a stop sign (probable). How: drink less, or not at all; the less you drink, the lower the risk. Do not hide the flush with antihistamines, antacids or products sold for the purpose, since that removes the warning and leaves the acetaldehyde. Why: the flush marks a slow-clearing enzyme and, with continued drinking, a substantially higher risk of cancer of the esophagus. Mismatch card: - System: The whole body, read on three clocks: genes over generations, development over a lifetime, physiology over days and weeks. - What it expects: The signals its long past supplied without anyone arranging them: hours on foot, real darkness, varied food, microbes, heat and cold, and familiar people close by. - What it gets: Too little of some signals (movement, daylight, fiber, company), too much of others (sugar, salt, evening light), and exposures that are new (nicotine is the classic example). - What happens in the gap: Many chronic diseases are suspected mismatches, graded chapter by chapter; local genetic tuning means the gap differs from person to person. - The handrail: Restore missing signals on the fastest clock, physiology, and judge every claim by the study behind it. (●●○) - Strength of evidence: ●●○ The measured gaps between past and present are well documented; evolutionary explanations for particular diseases are mostly hypotheses, and the doses come from trials. ### Chapter 3: The Body That Walks URL: https://www.spiralstaircase.com/book/3-the-body-that-walks Start here: - Walk every day, building toward 7,000 to 8,000 steps from wherever you are (strong, probable). How: add a walk with a destination, to a shop or a friend's door, and lengthen it over weeks, not days. Under sixty, the gains keep coming up to about 8,000 to 10,000. Some of it should be brisk, about a hundred steps a minute (Chapter 1 gives a fifteen-second check). Why: the steepest drop in risk comes at the bottom, from about 3,000 steps to 5,000, so the least active gain the most. - Break up sitting every half hour (probable). How: stand and walk for two to five minutes, whether a lap of the house, a trip to the water tap or the long way to the bathroom. Set a timer, or tie it to something that already happens, like the end of each call. Why: walking breaks blunt the rise in blood sugar after meals, and walking beats standing. - Swap your table salt for a potassium-enriched salt substitute (strong, probable). How: buy one that lists potassium chloride among its ingredients and use it for cooking and at the table; the big trial used about one part potassium chloride to three parts ordinary salt. Why: it cuts sodium and adds potassium in a single move, and it lowered strokes in the largest trial. Do not use it if you have kidney disease, take potassium-sparing diuretics or potassium supplements, or take any medicine that limits how you clear potassium. If you take any blood-pressure or heart medicine, ask a clinician first. The WHO guideline does not cover pregnancy or children. Mismatch card: - System: The walking body: leg muscles and joints, heart and blood vessels, lymph, back and feet. - What it expects: Hours on foot most days, rest in squats and on the ground, little salt and plenty of potassium, and use of a sore body while it heals. - What it gets: Nearly eight sedentary hours a day and about 5,100 steps for the average American, about 11 g of salt a day worldwide, and rest, scans and fear after injury. - What happens in the gap: Higher blood sugar within hours of sitting, blood pressure that climbs with age, knee arthritis in American skeletons that has doubled beyond what age and weight explain, and back pain that hardens into disability. - The handrail: Walk toward 7,000 to 8,000 steps, break up sitting, swap to potassium-enriched salt where safe, and keep moving through back pain (●●○) - Strength of evidence: ●●○ Trials firmly link movement, salt and potassium to blood sugar, blood pressure and pain, but the step numbers and the fitness link to long life rest on cohorts. ### Chapter 4: Load, Strength and Bone URL: https://www.spiralstaircase.com/book/4-load-strength-and-bone Start here: - Two strength sessions a week, 20 to 30 minutes each (strong). How: work every major muscle group, meaning legs, hips, back, chest and arms, on two separate days; the no-gym week below is one way. Why: in trials, training builds strength at every age studied; in cohorts, this amount is also linked to longer life (●●○). - Reach the daily protein range for your age (probable). How: for a 155-pound person, the official minimum is roughly 55 grams a day and the current US goal 85 to 110 grams. Over 65, do not drop below about 70 to 85 grams, the expert-group floor; the upper part of the US range suits active older adults. In lifting trials, more than about 110 grams stopped adding muscle. (Per pound of body weight: the minimum is a little over a third of a gram, the US goal half to three-quarters of a gram, the over-65 floor about half a gram.) A protein food at each meal, such as eggs, yogurt, fish, beans, tofu or meat, is the easy way to get there (Chapter 5 covers the rest of the plate). Why: enough protein helps training build a little more muscle, and expert panels judge that older muscle needs more. - Over 50, or told you have low bone mass: add heavier and impact loading, learned in person (probable). How: once the basic session feels easy, work with a physical therapist or qualified trainer toward heavier lifts and impact training (moves that jolt the skeleton, such as landing from a jump), as LIFTMOR's women did; the loads are heavy and form matters. If a trainer is out of budget, ask your doctor whether a physical therapy referral is covered. Why: this kind of training raised spine density in a trial of women with thin bones, while walking alone barely registers. Mismatch card: - System: Skeletal muscle and bone, which calibrate their strength to the loads they carry. - What it expects: Daily walking, carrying and lifting, often heavy, across a whole life. - What it gets: Chairs, wheels and machines; little that is heavy; and, for women, a menopausal transition that speeds bone loss with no extra load to answer it. - What happens in the gap: Strength falls faster than size, bone thins where load is missing, and the losses show up decades later as weakness, falls and fractures. - The handrail: Two short strength sessions a week, enough protein for your age, and heavier loading for bone after 50 (●●○). - Strength of evidence: ●●○ Resistance training reliably builds strength in trials, but the links to longer life come from cohorts, and the bone evidence rests on one heavy-lifting trial measured by density. ### Chapter 5: Eat URL: https://www.spiralstaircase.com/book/5-eat Start here: - Cut the ultra-processed share first, beginning with sugary drinks and processed meat (probable). How: swap sugary drinks, including energy drinks, for water, tea, coffee or sparkling water; keep juice to a small glass; make bacon, ham and hot dogs occasional; change what is in the cupboard, so the easy option at home is food that was recently an ingredient. Start with the meals you eat most often. Why: in controlled feeding, people ate about five hundred calories a day more on ultra-processed menus, and drinks and processed meat carry the clearest long-term signals. - Build meals on plants, legumes, and minimally processed protein and fats (probable). How: fill half the plate with vegetables and fruit, a quarter with whole grains or potatoes, a quarter with protein, often beans, lentils or fish; cook with olive or another liquid plant oil; add a handful of nuts most days. Work up to at least 25 grams of fiber a day, slowly, to limit gas; in practice that means beans or lentils most days, whole grains in place of white bread and rice, and fruit or vegetables at every meal. Include a fermented food with live cultures most days, such as plain yogurt, kefir or kimchi (●○○; one small trial, see Chapter 6). Why: this is the pattern with trial support for heart events, and it lowered blood pressure within weeks (●●● for blood pressure). - Drink to thirst (probable). How: water with meals and when thirsty; coffee, tea, milk and water-rich food all count. Drink more in heat and hard exercise, and in long events never drink past thirst. Why: thirst is the one intake signal the modern world has left mostly intact. Mismatch card: - System: Appetite and fuel: the gut, liver, muscle and fat, and the reward circuits that steer eating. - What it expects: Food that took work to get and time to chew, sugar wrapped in fiber, alcohol at a fraction of a percent, and water when thirsty. - What it gets: More than half its calories from ultra-processed food, sugar and alcohol in concentrated drinks, and little physical work. - What happens in the gap: People eat more without trying, surplus fat overflows into the liver and muscle, and diabetes climbs, as it did along the Gila. - The handrail: Fewer ultra-processed foods; meals built on plants, legumes and minimally processed protein and fats; water to thirst; little or no alcohol (●●○) - Strength of evidence: ●●○ Feeding trials and diet-pattern trials agree on direction; most food-by-food evidence is observational, and the best mix of fat and carbohydrate is still argued. ### Chapter 6: The Gut That Expects Dirt URL: https://www.spiralstaircase.com/book/6-the-gut-that-expects-dirt Start here: - Eat more fiber, from many kinds of plant (probable). How: beans or lentils most days (Chapter 5's third of a cup counts), whole grains instead of white, and a fruit or vegetable at every meal; frozen vegetables and canned beans count. A medium apple carries about 4 grams, so together these moves take a typical day from about 17 grams toward 25 or more. Build up slowly to limit gas. Why: it feeds the colon's bacteria, and high intakes are consistently linked to lower death rates. - Add one serving of fermented food with live cultures a day, and build up if you like it (emerging). How: a normal portion, such as a pot of plain yogurt, a glass of kefir, or a forkful or two of kimchi or sauerkraut from the chilled aisle; miso and most cheeses count too. Bread, vinegar pickles and heat-treated products carry no live microbes. Expect some bloating at first. Why: one small trial is promising, and cheap, old food has little downside. - Parents of babies: introduce peanut and well-cooked egg early, and keep them in the diet (strong, probable). Mismatch card: - System: The gut's microbes and the immune system's learned tolerance. - What it expects: Tens of grams of fiber a day from many plants; microbes from siblings, animals, soil and food; early tastes of lifelong foods; fever and care while sick. - What it gets: About 17 g of fiber a day (the US adult average), small families and indoor lives, needless antibiotics, delayed allergenic foods until recently, and fear of the thermometer. - What happens in the gap: Fewer gut species, more allergy, autoimmune disease diagnosed in about one person in ten in the UK over two decades (mostly women), resistant bacteria and returning measles. - The handrail: More fiber from more plants, a daily fermented food, early peanut and egg, antibiotics only when needed, vaccines on schedule. (●●○) - Strength of evidence: ●●○ Trials show food tolerance can be taught and vaccines work; fiber's links are strong but observational; proof that lost microbes cause disease in people rests largely on mice. ### Chapter 7: Light and Dark URL: https://www.spiralstaircase.com/book/7-light-and-dark Start here: - Get outdoor daylight early in your day, roughly 10 to 30 minutes (probable). How: within an hour of waking, step outside, not behind glass: walk part of the commute, coffee on the step, the dog. Longer when gray or shaded; open sky beats a courtyard; a lunchtime walk outside counts too. Sunglasses are fine. Why: morning light pulls the clock earlier, and outdoors is many times brighter than indoors. - Dim the last two to three hours before bed (probable). How: switch off overhead lights and use one or two low lamps, warm white if you are buying bulbs; turn screen brightness down. Many ordinary warm-white bulbs, kept low, already meet the level sleep researchers suggest for the evening. Why: an ordinary living room is bright enough to delay melatonin, and people differ so much in sensitivity that it is better to judge by your own sleep than to chase a number. - Get children outdoors about two hours a day; less still helps (strong). How: recess, walking to school, afternoons in the park, weekends outside. Shade and gray skies count; indoor sport did not show the same link. It matters most from school entry on, and in one trial a forty-minute outdoor class each school day helped. Why: outdoor time roughly halves new cases in trials, and Taiwan set two hours as its school target. It prevents new cases more than it slows existing ones (●○○ for slowing). Mismatch card: - System: The circadian clock, set through melanopsin in the eye; skin pigment and vitamin D; the growing eye. - What it expects: Bright days, truly dark nights, sun matched to skin and changing with the seasons, and a childhood spent largely outdoors. - What it gets: Days mostly indoors under room light far dimmer than any sky, evenings lit brightly enough to hold the clock back, lit bedrooms, pale skin under sudden holiday sun and dark skin in indoor lives, and classrooms instead of fields. - What happens in the gap: The clock drifts later, sleep timing scatters, vitamin D runs low in some skins while sunburn and skin cancer rise in others, and children's eyes grow too long. - The handrail: Morning daylight outdoors, dim evenings, a dark bedroom, unburnt sun matched to skin type, vitamin D where sun falls short, and two hours outside for children (●●○) - Strength of evidence: ●●○ Light's effect on the clock and outdoor time's effect on myopia rest on trials; the links from light to disease and death rest on observational cohorts, and vitamin D pills have not prevented major disease in adults who had enough. ### Chapter 8: Sleep URL: https://www.spiralstaircase.com/book/8-sleep Start here: - Get up at the same time every day, weekends included (probable). How: pick a wake time you can keep on your busiest day, and hold it on Saturday too. After a bad night, get up anyway. Why: regular timing predicted survival better than duration did in the largest measured study, though it is observational. - Make the bedroom dark, cool and quiet, with the phone charging somewhere else (probable, emerging). How: blackout curtains or a blind that works; tape or cover standby lights; let the room cool through the night and adjust the bedding instead of chasing a number on the thermostat; earplugs if noise wakes you. Put a cheap alarm clock by the bed and the phone across the room or outside it. Why: light late in the day pushes the body clock later, and screens in bed go with less sleep. - If insomnia has lasted three months or more, ask for CBT-I before sleeping pills (strong). How: ask your doctor for it by name. It works by telephone; in one trial it took six calls over eight weeks. Courses and apps also exist, so ask which ones your doctor trusts. Why: it is the recommended first treatment for every adult with chronic insomnia. Do not stop a prescribed sleep medicine abruptly without medical advice. Mismatch card: - System: The circadian clock and the sleep it schedules, tuned by light, temperature and routine. - What it expects: A bright day, a dark night that cools, and the same timing tomorrow; enough sleep, with room for naps. - What it gets: Dim days, lit evenings, a bedroom at one temperature with a phone in it, a schedule that lurches at weekends, afternoon caffeine, and for some, work through the night. - What happens in the gap: Sleep moves later and grows irregular; insomnia is common and often untreated; night workers live against their own clocks; apnea goes undiagnosed, especially in women after menopause. - The handrail: A fixed wake time, a dark and cooling bedroom without a phone, CBT-I for chronic insomnia, and snoring taken seriously. (●●○) - Strength of evidence: ●●○ CBT-I and the apnea treatments rest on trials; the regularity link rests on a large but observational cohort; the shift-work fixes on laboratory simulations. ### Chapter 9: Heat and Cold URL: https://www.spiralstaircase.com/book/9-heat-and-cold Start here: - Let your home move a little: cooler rooms in winter, and a bedroom that cools at night (emerging). How: in winter, set the thermostat around 64 to 66°F and add a sweater rather than a degree; turn the heat down at bedtime so the bedroom cools overnight (Chapter 8 covers sleep). Why: a few weeks of mild cold grew brown fat and improved insulin sensitivity in tiny trials. Safety: the World Health Organization treats 64°F as a safe indoor floor in cold seasons, and older people, infants and anyone with heart or lung disease may need it warmer. - End your shower with thirty seconds of cold, if you like it and your heart is healthy (probable, emerging). How: finish a normal warm shower with thirty seconds of cold; longer did no better. Breathe slowly through the first gasp. Why: in the one large trial, it cut sickness absence by about three in ten, though not illness itself. Safety: with heart disease or an irregular heartbeat, ask a clinician first. - Heat: a sauna or a hot bath, a few times a week, if you have access and enjoy it (emerging). How: about a quarter of an hour in a sauna, or a hot bath around 104°F for ten minutes or so. Taken an hour or two before bed, a warm bath or shower shortened the time people took to fall asleep in pooled studies (Chapter 8). Why: two large cohorts link regular heat with fewer heart deaths (that link is ●●○; the frequency is untested), and small trials show better artery function in unfit people. Safety: no alcohol, drink water, rise slowly, and see "Safety" below. Mismatch card: - System: Thermoregulation: skin blood flow, shivering muscle, brown fat, sweating and the heart's response to heat. - What it expects: Days and seasons that leave the comfortable band: cool mornings, warm afternoons, nights that cool, and occasional real cold and real heat. - What it gets: A narrow indoor band all year, most of life spent inside, offices set for a man in a suit, and summers whose humid heat can outrun the body's cooling. - What happens in the gap: Cold acclimatization fades within a few years of the signal stopping, as the haenyeo showed, though the metabolic cost appears small, and a body that rarely meets heat has had no practice at shedding it. - The handrail: Mild, regular swings in both directions: cooler rooms, a brief cold finish to the shower, sauna or hot baths, and respect for cold water and humid heat (●○○ to ●●○) - Strength of evidence: ●●○ Acclimatization and its loss are well documented, and regular heat tracks lower cardiovascular death in two cohorts, but the cold trials are small, the one large shower trial measured absence rather than illness, and several heat trials are null. ### Chapter 10: Green and Quiet URL: https://www.spiralstaircase.com/book/10-green-and-quiet Start here: - Spend about two hours a week somewhere green, including city parks (probable). How: four half-hour visits, or one long weekend walk, in any park, riverside, woodland or beach. Why: in a large English survey the benefit started around two hours, though a survey cannot prove direction. - Protect your hearing from loud noise (strong). How: use the arm's-length test. If you must raise your voice to talk to someone beside you, keep the time short, step away from the speakers, or wear earplugs; at concert volumes the safe daily allowance runs out within an hour. With headphones, keep the volume low enough to hear someone next to you. Why: noise damage to hearing is permanent and avoidable. - Get a hearing test if you are over 50 or struggling to follow conversation (probable). How: ask your doctor or an audiologist, and mention any ringing. One warning sign the Food and Drug Administration lists: "You find it hard to follow speech in groups." In the United States, hearing aids for perceived mild to moderate loss have been sold over the counter since 2022, without a prescription or exam. Why: hearing loss is common, undertreated and easy to miss in yourself; no age is backed by a trial, and 50 is simply a sensible point to stop guessing. Mismatch card: - System: The stress system, attention and the heart, tuned by a living landscape; hearing, and the threat circuit it feeds. - What it expects: Daylight hours among plants, water and animals, and a quiet natural background broken by occasional sounds worth noticing. - What it gets: Most of life indoors, a view of a wall, and mechanical noise that never stops, including at night, with bursts loud enough to damage the ear. - What happens in the gap: Slower stress recovery, more psychiatric diagnoses among children raised in the least green places, extra heart and lung deaths where the trees go, broken sleep, and avoidable hearing loss on a population scale. - The handrail: Two hours a week somewhere green, the arm's-length test for loud noise, a quiet bedroom, and a hearing test if conversation gets harder or once you are past 50 (●●○) - Strength of evidence: ●●○ Natural experiments, twin and mover designs and a randomized trial point the same way for green space, but individual effects are modest; noise exposure limits are solid, the noise-and-heart link is observational, and hearing aids have not been shown to prevent dementia. ### Chapter 11: The Social Animal URL: https://www.spiralstaircase.com/book/11-the-social-animal Start here: - Name your three to five people, and schedule them (probable). How: write down the people you would call at two in the morning, and who would call you. Give each a recurring slot, in person where you can and a call where you cannot: the same Tuesday, the same table, the same walk. No trial has tested a dose, so pick a rhythm you can keep, such as a real conversation with one of them every week. If you can write only one name, or none, start there: pick one dormant tie, an old friend, a sibling or a former colleague, and send one message this week suggesting a specific time. Why: the health evidence points at the quality of a few close ties, not the size of a network. - Join one standing weekly thing done with other people (emerging). How: a class, a choir, a team, a volunteer shift, a shared meal. Same time, same faces, and if you can, something done together in time, such as singing, dancing, rowing or a group class. Choose what you will still be doing in three months over what sounds best. Why: recurrence is the likeliest way to build the ties linked to longer life, though that part is inference; moving in time raised closeness in single sessions. - Expecting or raising young children? Recruit helpers on purpose, before you need them (emerging). How: before the birth, line up specific people for specific jobs: meals, a night off, laundry, an adult to talk to at midday. If there are two of you, agree in advance who covers which nights. Ask in detail; offers of help tend to arrive vague. Why: low support is among the strongest predictors of depression after birth; no trial has tested a particular arrangement. Mismatch card: - System: The social brain and the stress physiology it regulates, from the threat circuitry that registers exclusion to the hormones that respond to touch. - What it expects: Daily, face-to-face contact with a small, stable group; touch as an ordinary event; many hands around every infant, from labor onward. - What it gets: A wide, thin network through a screen, inner circles left to chance, labor attended by rotating staff, and new parents largely alone behind a closed door. - What happens in the gap: Higher mortality among isolated and lonely people across dozens of cohorts, loneliness and depression in new parents, and a stress system that loses one of its regulators. - The handrail: Three to five named people on a schedule, a standing weekly activity with others, touch where it is welcome, continuous labor support and help recruited before a birth (●●○) - Strength of evidence: ●●○ The mortality association is large and consistent but observational; the mechanisms and the labor-support effect rest on small or low-quality trials. ### Chapter 12: Attention in the Age of the Phone URL: https://www.spiralstaircase.com/book/12-attention-in-the-age-of-the-phone Start here: - Charge the phone outside the bedroom (probable, emerging). How: a charger in the kitchen or hall and a cheap alarm clock by the bed. Why: an expert panel agreed that screen use before bed harms sleep in children and teens, where the evidence is firmest; among young adults, more screen time in bed goes with more insomnia and less sleep (Chapter 8). - Turn off every notification that is not a person (emerging). How: in settings, leave on calls and messages from people; switch off news, shopping, games, likes and "you might have missed". Why: every alert is one more unpredictable payout on the slot-machine schedule. No trial has tested this on its own, but the cost of trying is a few minutes. - Use AI like a spotter, not a stand-in, whenever you want to learn or keep a skill (probable). How: ask for a hint, a question or a check of your own attempt before any finished answer; if the tool allows it, tell it to tutor rather than solve. Why: in the Turkish trial, the version that withheld answers gave the biggest gains and no exam penalty, while full answers cost students on the exam. If the only goal is the output, this does not apply. Mismatch card: - System: The reward circuit that learns from unpredictable payouts; the default network that runs during idle time; memory, navigation and reasoning that improve with use; and a child's play-driven development. - What it expects: Rewards that are earned, spaced and often absent; long stretches with nothing to attend to; problems solved with your own equipment; and childhood days of free, mixed-age, outdoor play. - What it gets: A pocket device engineered for time on device, paying out on a variable schedule and filling every gap; tools that supply the answer before the effort starts; and childhoods with hours of screens and the risk designed out. - What happens in the gap: Checking that resists unlearning, idle minutes that vanish, work that looks better while the person doing it learns less, and afternoons a phone ban empties but does not refill. - The handrail: The phone out of the bedroom, notifications from people only, AI as a spotter, phone-free times, free outdoor play for children (●●○) - Strength of evidence: ●●○ One large randomized trial on adult social media and one strong field trial on AI and learning, set against a genuinely open argument about teenagers and a thin, mostly observational literature on play. ### Chapter 13: Stress and the Mind URL: https://www.spiralstaircase.com/book/13-stress-and-the-mind Start here: - Move most days, in whatever form you will keep doing (strong). How: walking or jogging, yoga, strength training or tai chi all counted in the trials. Build toward the 150 minutes a week of moderate activity that Chapter 3 sets out, and let some sessions get brisk enough to leave you breathing hard. A depressed body does not start at a runner's baseline, so begin with ten minutes out the door and build. Why: exercise produced moderate drops in depressive symptoms, and more intense sessions did somewhat more. - Practice slow breathing or mindfulness for five to ten minutes a day, or take an eight-week course (probable). How: breathe about six times a minute, roughly four seconds in and six out, sitting down, on most days; use a count, an app or a prayer to keep the pace. For anxiety that persists, consider an eight-week mindfulness-based stress reduction course. Why: small-to-moderate reductions in stress and anxiety in trials, and one course proved no worse than a standard drug for anxiety disorders. - Talk to a clinician if low mood or anxiety lasts more than two weeks or gets in the way of work, sleep or people (strong). How: a family doctor is a fine first stop. Before the appointment, write down what you have noticed, for how long, and what it is costing you in sleep, work and time with people, because a low day in the waiting room can make a hard month sound like nothing. Ask about the options, including talking therapy; if cost or a waiting list is the barrier, say so and ask about lower-cost and online options. Why: every antidepressant tested beat placebo; the wrong chemical story never meant the treatment was wrong. If you already take a psychiatric medicine, keep taking it; any change belongs in a conversation with the person who prescribed it. Mismatch card: - System: The stress response, fast adrenaline and slow cortisol, with the defensive emotions it drives: fear, anxiety and low mood. - What it expects: Threats that are physical, local and short, answered with the body, among allies who help solve problems. - What it gets: Uncontrollable judgment without end, low control at work, long hours, thin company and short sleep. - What happens in the gap: Alarms built to over-fire go off constantly and stop resetting; the daily cortisol rhythm flattens, tissues stop hearing it, inflammation runs on, and anxiety and low mood are common. - The handrail: Movement most days, slow breathing or a mindfulness course, trusted company and control over your hours, and treatment when symptoms persist (●●○) - Strength of evidence: ●●○ Treatment effects and stress gradients rest on large trials and cohorts; the evolutionary explanations remain hypotheses, and the effect of adult stress on disease is moderate. ### Chapter 14: Wanting, Loving, Losing, Meaning URL: https://www.spiralstaircase.com/book/14-wanting-loving-losing-meaning Start here: - Invest in the quality of your closest relationship, and get couple therapy if it is in trouble (probable, strong). How: set a fixed, phone-free time together each week, even half an hour after the children are in bed, and when an argument turns hostile, stop and come back to it later. If the relationship is distressed, find a couple therapist, or start with a structured online program such as OurRelationship if cost or access is a barrier. Why: quality, not status, carries the health link, and couple therapy has large effects. - Take on a recurring role, about two hours a week (probable). How: a volunteering shift, a standing commitment to a person or a group that meets regularly and expects you, a project that would go undone without you. Put it on the calendar like a class. Why: purpose and regular volunteering are consistently linked to lower mortality, though no trial has shown they cause it. - If a substance or habit has a grip, change your surroundings, and ask about medicine alongside it (probable, strong). How: take the supply out of the house, change the routes, places and company tied to use, and put something rewarding in the gap, ideally something with people in it. If you have been drinking heavily for a long time, talk to a doctor before you stop. If you drink too much, ask a doctor about acamprosate or naltrexone; for opioids, ask about methadone or buprenorphine. Your doctor sets the dose, and before starting naltrexone, tell your doctor about every medicine you use, especially opioid painkillers. Why: the veterans' surroundings changed and most stopped, and the medicines help many who need more than that; a new setting does not replace treatment for a moderate or severe disorder. - After a death, lean on people (probable). How: accept help with meals, errands and paperwork in the first weeks and months. If grief still dominates daily life six to twelve months on, ask for grief-specific therapy (●●●), such as complicated grief treatment. Why: most people adapt without treatment, and for those who do not, a targeted therapy works. Mismatch card: - System: The reward system (dopamine-driven wanting) and the attachment systems that bond, grieve and seek a role. - What it expects: Rewards that are scarce, variable and diluted; a partner and a small group met every day; losses mourned with others; a role the group depends on. - What it gets: Pure, cheap, constant drugs and betting on a phone, with close relationships, mourning and purpose left to arrange themselves. - What happens in the gap: Substance use disorders in about 15 percent of Americans aged twelve and over, just over half of them mild; a rise in mortality after bereavement, sharpest in the first months and in men; higher mortality with low purpose in cohorts. - The handrail: Tend the closest relationship; keep a recurring role; change the setting and use the treatments that work; lean on people after a loss (●●○) - Strength of evidence: ●●○ The treatments for addiction, couples and prolonged grief rest on trials; the links from relationships, purpose and belonging to longer life rest on large but confounded cohorts. ### Chapter 15: Women's Bodies Across the Life Course URL: https://www.spiralstaircase.com/book/15-womens-bodies-across-the-life-course Start here: - In the reproductive years, track your cycle as a vital sign (probable). How: note the first day of each period, how long it lasts and how heavy it is, in any calendar or app, and watch for change from your own pattern. Why: the cycle reports on energy, iron loss, hormones and, later, the start of the transition, for free. - In perimenopause, take your symptoms to a clinician, because effective treatments exist (strong). How: book an appointment for this alone, with a list: flushes, night sweats, sleep, mood, vaginal or urinary symptoms, and changes in bleeding. Ask about hormone therapy, including a patch or gel, and about the non-hormonal options. Why: hormones treat flushes best, and for healthy women under sixty or within ten years of menopause the balance is favorable. - At every stage, lift (strong, probable). How: two strength sessions a week of about thirty minutes. The home session in Chapter 4 needs only a chair, a wall and a loaded bag; add load until the last few repetitions feel hard. After fifty, or with low bone mass, work toward heavier lifts and impact training taught in person. Why: bone loss is fastest around the final period, lean mass falls across the transition, and supervised heavy lifting twice a week built spine bone in women with low bone mass, while walking alone does little. Mismatch card: - System: The female reproductive axis across a lifetime, from first period through pregnancy to the transition and the decades after it. - What it expects: A first period in the mid-teens, many pregnancies with long breastfeeding between them and about a hundred periods in a lifetime, food that matches effort, kin nearby, and a working body that carries loads through the transition. - What it gets: Earlier first periods, fewer and later births, short breastfeeding and about four hundred periods; energy deficits in some and surpluses in others; grandmothers far away; and a transition lived mostly sitting down. - What happens in the gap: More hormone-driven cancers and more iron lost; periods that stop from low energy; common conditions such as PCOS and endometriosis diagnosed late; symptoms of the transition endured instead of treated; bone and muscle lost fastest just as loading falls. - The handrail: Track the cycle, take perimenopausal symptoms to a clinician, lift at every stage (●●○) - Strength of evidence: ●●○ The treatments for flushes, the contraception risks and the pregnancy heart flags rest on trials and large cohorts; the evolutionary accounts of menopause and PCOS, and the timing hypothesis, do not. ### Chapter 16: Aging Well URL: https://www.spiralstaircase.com/book/16-aging-well Start here: - Keep up the five things in Chapter 1 (strong). How: don't smoke, drink little or nothing, walk toward seven or eight thousand steps a day, cut the ultra-processed share of your food, keep a regular wake time, and see your three to five people. Why: on this book's reading, they act on six of the ten leading causes of death. - Get the screenings due for your age and sex (strong). How: go through the table above with your clinician once, put the due dates in a calendar, and set reminders for the repeats. Why: for most rows the Task Force judged that benefits outweigh harms for people at average risk. - Keep your strength and grip (strong, probable). How: twice a week, about half an hour: sit-to-stands from a dining chair (a cushion raises the seat if your knee complains), push-ups against a wall or counter, rows with a band, and a heavy shopping bag carried in each hand (Chapters 1 and 4). Once or twice a year, count how many times you can stand up from a chair in thirty seconds without using your hands, and write it down; treat a poor score as a reason to train rather than a forecast. Why: strength falls faster than muscle bulk with age, and weakness predicts disability and earlier death. Mismatch card: - System: The whole body over a lifetime: the cells that age and occasionally turn cancerous, and the organs that fail at the end. - What it expects: Daily physical work, food that comes and goes, constant company and microbes, and death arriving mostly from outside, after a modal age in the seventies. - What it gets: Low physical load, constant food, tobacco and alcohol, and medicine that postpones death from diseases whose causes remain in place. - What happens in the gap: Longer lives with a wider strip of illness at the end; in the United States, the widest gap between lifespan and healthy lifespan of 183 countries studied. - The handrail: The five things in Chapter 1, the screenings due for your age and sex, and kept strength (●●○). - Strength of evidence: ●●○ Screening rests on trials and quitting smoking on large, consistent cohorts; the links between strength, lifestyle and a shorter sick spell at the end come from cohorts and population data. ## The 30-day protocol Before you start. See a clinician before starting if you have heart disease, diabetes, pregnancy, a past fracture, or take regular medication; specific cautions appear beside each step. Every action below has already appeared in a chapter, with the evidence behind it and the reasons to hold it loosely. This appendix adds an order: one layer of signal a week, starting with the ones that cost nothing. Thirty days will not move the outcomes most of this book is about; those were measured over years. What a month can do is change the room you live in. A behavior you decide on every morning stays a decision forever, and decisions run out by Thursday. A behavior your surroundings supply runs without you. So treat these four weeks as installation, not effort: arrange a house, a commute and a calendar so that when the month ends, most of this keeps happening while you think about something else. One rule has no exceptions. Nothing here replaces medical care, and nothing here is a reason to stop, skip or change a prescribed treatment without the clinician who prescribed it. The month at a glance: - Week | The layer | Start with | Minimum version - One | Walking and light | A longer daily walk, and daylight within an hour of waking | Outdoors after waking, and one walk you did not take last week - Two | Strength and sleep | Two short strength sessions, and one wake time for seven days | The wake time, held on Saturday - Three | Food and drink | Swap the meals you eat most often | One repeated meal rebuilt from ingredients - Four | People, attention and green space | Name your people and put them in the calendar | One shared meal with the phone in another room - Last two days | Review | Keep what installed itself, and drop something | Answer one question per habit ### Week One: Walking and Light - First: Walk more than you do now, toward seven or eight thousand steps. How: Add one twenty-minute walk a day, about two thousand brisk steps; walk to something, on a fixed route, at a fixed time. Grade: strong for the curve, probable for the number. - Second: Get outdoor daylight early. How: Ten to thirty minutes within an hour of waking, outdoors and not behind glass; longer when gray. Grade: probable. - Third: Break up sitting every half hour. How: Stand and walk for two to five minutes; tie it to the end of each call. Grade: probable. - Fourth: Dim the last two to three hours before bed. How: Overhead lights off, one or two low lamps, screen brightness down. Grade: probable. - Fifth: Use the bursts you already have. How: Three or four times a day, a minute or two hard enough that talking gets awkward: a hill walked hard, a heavy bag carried quickly. Grade: probable. Minimum version: Outdoors within an hour of waking, and one walk you did not take last week. Both are free. Cautions: Build up over weeks, not days; sore feet and shins are the usual price of a sudden jump. If you have chest pain, breathlessness out of proportion to effort, fainting or known heart disease, see a clinician before you add hard bursts. For most people the risk of vigorous exercise is tiny, and lower still in those who do it regularly, so build up rather than avoid it. With diabetes or numb feet, do not go barefoot or switch to minimal shoes without your clinician, and check your feet daily. If you take insulin or a sulfonylurea, watch for low blood sugar as your activity rises. Never look at the sun; sunglasses are fine on the morning walk. ### Week Two: Strength and Sleep - First: Two strength sessions a week, twenty to thirty minutes each. How: Sit-to-stands from a chair, push-ups against a wall or counter, a hip bridge, rows with a band or loaded backpack, step-ups, a carry. Grade: strong. - Second: Get up at the same time every day, weekends included. How: Pick a time you can keep on your busiest day; after a bad night, get up anyway. Grade: probable. - Third: Make the bedroom dark and let it cool, with the phone charging somewhere else. How: Curtains that work, standby lights covered, bedding adjusted instead of the thermostat, a cheap alarm clock by the bed. Grade: probable for dark; emerging for cool and for the phone. - Fourth: Reach the protein range for your age. How: A protein food at every meal: eggs, yogurt, fish, beans, lentils, tofu or meat. Grade: probable. - Fifth: Stop caffeine at least six hours before bed. How: If you sleep at eleven, the last coffee, tea, cola or energy drink is by five. Grade: probable that it costs sleep; emerging for the exact cutoff. Minimum version: One wake time, seven days, Saturday included. It costs no time at all, and it is the habit that organizes the others. Cautions: With osteoporosis or a past fracture from a minor fall, start strength work under supervision, and do heavier or impact training only under supervision. With heart disease, a recent injury, or chest pain or breathlessness with effort, see a clinician first. Sharp or worsening joint pain means stop and get it checked. With kidney disease, ask before raising protein. If you are over sixty or get up in the night, keep a dim, low night light on the route to the bathroom; a fall costs more than a little light. ### Week Three: Food and Drink - First: Cut the ultra-processed share, starting with sugary drinks and processed meat. How: Rebuild your most repeated meals from ingredients: oats and fruit instead of a packaged bar, beans, eggs or leftovers instead of a vending-machine lunch; water, tea, coffee or sparkling water instead of sugary and energy drinks. Grade: probable. - Second: Eat more fiber, from many kinds of plant. How: Beans or lentils most days, whole grains instead of white, a fruit or vegetable at every meal; build toward twenty-five grams a day. Grade: probable. - Third: Drink less alcohol, or none. How: Two standard drinks a week or fewer is the low-risk line; start with alcohol-free days, and do not keep it in the house as a default. Grade: probable for mortality; strong that it causes cancer. - Fourth: Swap table salt for a potassium-enriched salt substitute. How: Use it wherever you salt food at home; check the caution below first. Grade: strong for blood pressure; probable for strokes and deaths. - Fifth: Add one serving of fermented food with live cultures a day. How: Plain yogurt, kefir, or a forkful of kimchi or sauerkraut from the chilled aisle. Grade: emerging. Minimum version: One meal you repeat every week, rebuilt from things that were recently ingredients. Cautions: The salt substitute comes with the strongest warning in this appendix. Do not use it if you have kidney disease, take potassium-sparing diuretics or potassium supplements, or take any medicine that limits how you clear potassium. If you take any blood-pressure or heart medicine, ask a clinician first. Build fiber up slowly and expect some gas and bloating at first; with irritable bowel syndrome, inflammatory bowel disease or a past bowel obstruction, ask a clinician before raising it. If you are pregnant, over sixty-five or have a weakened immune system, avoid milk, yogurt and cheese made from unpasteurized milk, because of the risk of Listeria. If you have been drinking heavily every day for a long time, do not stop suddenly without medical advice, because withdrawal can be life-threatening; medicines and treatment exist. If you are pregnant, the advice on alcohol is none. ### Week Four: People, Attention and Green Space - First: Name your three to five people, and schedule them. How: Write down who you would call at two in the morning; give each a recurring slot, in person where you can and a call where you cannot. Grade: probable. - Second: Spend about two hours a week somewhere green. How: Four half-hour visits, or one long weekend walk; city parks, riversides and beaches count. Grade: probable. - Third: Join one standing weekly thing done with other people. How: A class, a choir, a team, a volunteer shift; same time, same faces; choose what you will still be doing in three months. Grade: emerging. - Fourth: Make meals, the first and last hour of the day, and the conversations that matter phone-free. How: Phone in another room, not face down on the table; turn off every notification that is not a person. Grade: emerging. - Fifth: Slow your breathing for five to ten minutes most days. How: About six breaths a minute, four seconds in and six out, sitting down. Grade: probable. Minimum version: One shared meal with the same people, phone in another room. Cautions: Withdrawal is a symptom as well as a cause. If low mood or anxiety lasts more than two weeks, or gets in the way of work, sleep or people, talk to a clinician; treatment works, and no walking group replaces it (●●●; Chapter 13). With thoughts of suicide or self-harm, do not wait: in the US, call or text 988, or elsewhere your local emergency number. Do slow breathing sitting or lying down. Never practice fast breathing or breath-holds in or near water, in the bath or while driving, and skip them if you are pregnant or have heart disease or a seizure disorder. Outdoors, ticks live in grassy, brushy and wooded areas, so use a registered repellent and check yourself when you get home. Keep one phone route open for anyone who depends on reaching you, and for any medical alerts. Full appendix, with the tracks for particular lives: https://www.spiralstaircase.com/protocol ## Glossary - Allostatic load: The cumulative cost of holding the body ready, named by McEwen and Stellar in 1993 and estimated from markers such as blood pressure, waist, lipids and stress hormones. (https://www.spiralstaircase.com/glossary/allostatic-load) - Analytical rumination hypothesis: The proposal that depression's symptoms package the mind for sustained thought about a hard social problem. It is one of three competing evolutionary accounts of low mood. (https://www.spiralstaircase.com/glossary/analytical-rumination-hypothesis) - Atherosclerosis: The build-up of fatty, often calcified plaque in artery walls. It is ancient, found in mummies, yet 85% of Tsimane adults scanned had no coronary calcium at all. (https://www.spiralstaircase.com/glossary/atherosclerosis) - Australopithecus: A genus of early hominins, including Lucy at 3.2 million years old, that walked upright while still climbing regularly. (https://www.spiralstaircase.com/glossary/australopithecus) - Autophagy: The cell's system for digesting and recycling its own worn-out parts. It joined the hallmarks of aging in 2023, and nobody can yet measure it in a living person. (https://www.spiralstaircase.com/glossary/autophagy) - Biophony: Bernie Krause's term for the collective voice of a habitat's organisms, set beside geophony, the sound of wind and water, and anthropophony, the sound people make. (https://www.spiralstaircase.com/glossary/biophony) - Blue Zones: Regions, Sardinia, Okinawa and Ikaria among them, said to hold unusual numbers of very old people. Saul Newman's analysis, a preprint contested by Blue Zones researchers, reports that such claims track missing or unreliable birth records. (https://www.spiralstaircase.com/glossary/blue-zones) - Brown fat: Fat tissue that makes heat rather than storing energy, switched on by cold. Its output in adults runs to roughly 15 to 25 kilocalories a day: a pilot light, not a boiler. (https://www.spiralstaircase.com/glossary/brown-fat) - Central sensitization: A prolonged but reversible rise in the excitability of nerve cells in the spinal cord and brain, so touch hurts and pain hurts more. (https://www.spiralstaircase.com/glossary/central-sensitization) - Choice architecture: The way defaults and framing shape what people do without removing any option, as in automatic pension enrollment and presumed consent for organ donation. (https://www.spiralstaircase.com/glossary/choice-architecture) - Circadian rhythm: The roughly 24-hour cycle kept by a self-winding genetic loop found in tissues throughout the body. In dim, controlled conditions the human clock's period averages 24.18 hours. (https://www.spiralstaircase.com/glossary/circadian-rhythm) - Cognitive reserve: Yaakov Stern's account of why two people with similar Alzheimer's pathology can differ greatly in impairment. Education, complex work and hard mental activity track the gap. (https://www.spiralstaircase.com/glossary/cognitive-reserve) - Cold shock response: The involuntary gasp, hyperventilation and surge in blood pressure that follow sudden skin cooling. It peaks in water of 10 to 15°C (50 to 59°F) and is thought to cause most open-water immersion deaths, long before body temperature falls; it habituates after about four immersions. Never swim alone or after alcohol, and ask a clinician first if you have heart disease or an arrhythmia. (https://www.spiralstaircase.com/glossary/cold-shock-response) - Compression of morbidity: James Fries's 1980 proposal that illness at the end of life could be squeezed into a shorter span if its onset were delayed faster than death. Measured as the distance between life expectancy and healthy life expectancy, the gap has widened instead, though whether morbidity has genuinely expanded remains an open argument. (https://www.spiralstaircase.com/glossary/compression-of-morbidity) - Concealed ovulation: The absence of any outward signal of human fertility. Paternity confidence, paternity confusion and alliance-building all have advocates, and no test has settled the question. (https://www.spiralstaircase.com/glossary/concealed-ovulation) - Constrained total energy expenditure: Herman Pontzer's proposal that daily energy use levels off as activity rises, because active bodies spend less elsewhere. Hadza foragers burn no more than Westerners their size. (https://www.spiralstaircase.com/glossary/constrained-total-energy-expenditure) - Cooperative breeding: A system in which adults besides the mother, called alloparents, invest in raising young: grandmothers, older siblings, aunts, unrelated group members. Human infants arrive too helpless for one adult to manage. (https://www.spiralstaircase.com/glossary/cooperative-breeding) - Correlated progression: T.S. Kemp's account of how warm blood evolved: many structures changing together, keeping the animal a working whole at every step. It gives this book its first principle, that nothing works alone. (https://www.spiralstaircase.com/glossary/correlated-progression) - Cortisol: The main human glucocorticoid, released tens of minutes into a stress response. It permits, stimulates and prepares the response and also shuts it down: the accelerator and much of the brake. (https://www.spiralstaircase.com/glossary/cortisol) - Default mode network: Brain regions, including medial prefrontal and posterior cingulate cortex, that grow more active when no task holds the mind. They handle memory, imagining the future and reading other people. (https://www.spiralstaircase.com/glossary/default-mode-network) - Dogon: Millet farmers of Mali whose menstrual huts let Beverly Strassmann count women's cycles. A Dogon woman who lived to menopause had a median of about 109 periods. (https://www.spiralstaircase.com/glossary/dogon) - Drunken monkey hypothesis: Robert Dudley's proposal that the smell of ethanol in ripening fruit led ancestral primates to food, and that modern drinking misfires that attraction. Wild chimpanzee fruit averages 0.3% ethanol. (https://www.spiralstaircase.com/glossary/drunken-monkey-hypothesis) - Dunbar's number: About 150, extrapolated from a relationship between neocortex size and group size across primates. A 2021 reanalysis concluded that specifying any one number is futile: active networks often land in the low hundreds, but whether the brain fixes a limit at 150 is disputed. (https://www.spiralstaircase.com/glossary/dunbars-number) - Dysevolution: Daniel Lieberman's term for the loop in which medicine treats the symptoms of mismatch diseases while the environments causing them are passed on. (https://www.spiralstaircase.com/glossary/dysevolution) - Eccrine sweat glands: The two to four million glands that cool the body by evaporation, about 10 times denser in human skin than a chimpanzee's and not tied to the rhythm of breathing. (https://www.spiralstaircase.com/glossary/eccrine-sweat-glands) - Emmetropization: The feedback loop that grows the eyeball until its length matches its focusing power, using blur on the retina as its guide. Starved of bright daylight in childhood, it overshoots. (https://www.spiralstaircase.com/glossary/emmetropization) - Endothermy: Making your own body heat, at five to ten times a cold-blooded animal's oxygen cost. The main jump in the mammal line is currently dated to about 233 million years ago. (https://www.spiralstaircase.com/glossary/endothermy) - Energy availability: Dietary energy in, minus energy burned in exercise, per kilogram of fat-free mass. Below about 30 kcal per kilogram a day, the hormone pulses that drive ovulation are disrupted. (https://www.spiralstaircase.com/glossary/energy-availability) - EPAS1: A gene in the oxygen-sensing pathway. Tibetan variants, inherited from Denisovans, hold down the red-cell response to thin air and spare the heart the strain of thickened blood. (https://www.spiralstaircase.com/glossary/epas1) - Epidemiologic transition: Abdel Omran's 1971 framework describing a shift from an age of pestilence and famine, through receding pandemics, to an age of degenerative and man-made diseases. (https://www.spiralstaircase.com/glossary/epidemiologic-transition) - Epigenetic regulation: Chemical marks on DNA and its packing proteins that change how genes are read without changing the sequence. They answer the environment within a lifetime; passage to an unexposed descendant is unproven in humans. (https://www.spiralstaircase.com/glossary/epigenetic-regulation) - Evidence grades: This book's three marks, a simplified cousin of the GRADE system: ●●● strong, ●●○ probable, ●○○ emerging, small, animal-only or contested. (Prologue) (https://www.spiralstaircase.com/glossary/evidence-grades) - Evolutionary medicine: The study of why bodies are vulnerable to disease, called Darwinian medicine by Williams and Nesse in 1991. Its founding move: diseases have no evolutionary explanations, but vulnerabilities do. (https://www.spiralstaircase.com/glossary/evolutionary-medicine) - Evolutionary mismatch: A condition more common or severe because an organism is imperfectly adapted to a novel environment. Three tests apply: commoner in the new setting, traceable to a changed factor, explained by a mechanism. (https://www.spiralstaircase.com/glossary/evolutionary-mismatch) - Expensive tissue hypothesis: Aiello and Wheeler's 1995 proposal that the human brain was paid for by a shrunken gut. Broader comparisons found no trade-off, and direct measurement suggests humans simply burn more energy. (https://www.spiralstaircase.com/glossary/expensive-tissue-hypothesis) - Fiber: Carbohydrate human enzymes cannot break down, left for colon bacteria to ferment into short-chain fatty acids. American adults average about 17 g a day; pooled benefits peaked at 25 to 29 g. (https://www.spiralstaircase.com/glossary/fiber) - Forest bathing: Shinrin-yoku, named by a Japanese ministry in 1982. Its immune claims rest on very small unrandomized studies; the better-measured effects are modest short-term falls in cortisol and blood pressure. (https://www.spiralstaircase.com/glossary/forest-bathing) - Functional hypothalamic amenorrhea: Periods stopping because the reproductive axis has shut down under low energy availability. It can occur without visible weight loss and needs clinical assessment. (https://www.spiralstaircase.com/glossary/functional-hypothalamic-amenorrhea) - GLP-1: A gut hormone released after a meal that boosts insulin, slows stomach emptying and reduces eating. Drugs built from it produce large weight loss that mostly reverses on stopping, so they are prescription treatments to choose with a clinician and plan as long-term care. (https://www.spiralstaircase.com/glossary/glp-1) - Glymphatic system: A proposed route by which fluid enters the brain along arteries and leaves along veins, carrying waste. Whether sleep speeds that clearance or slows it is disputed. (https://www.spiralstaircase.com/glossary/glymphatic-system) - Grandmother hypothesis: Kristen Hawkes and colleagues' proposal that older women's foraging pays for human life history, letting mothers wean earlier and conceive again sooner. (https://www.spiralstaircase.com/glossary/grandmother-hypothesis) - Hadza: Hunter-gatherers of Tanzania, roughly 1,200 of them, the most-studied foraging population in this book. They are contemporaries rather than ancestors, and many now choose settled camps and villages. (Prologue) (https://www.spiralstaircase.com/glossary/hadza) - Haenyeo: Women divers of Jeju, Korea. Before wetsuits arrived in 1977 their winter metabolic rate ran about 35% above the standard; within a few years of covering up, the adaptation was gone. (https://www.spiralstaircase.com/glossary/haenyeo) - Hallmarks of aging: Twelve cellular processes named in a 2023 review, from telomere attrition to chronic inflammation. A candidate qualifies only if it appears with age, speeds aging when accentuated, and slows it when treated. (https://www.spiralstaircase.com/glossary/hallmarks-of-aging) - Handrail: This book's name for the practical section closing most chapters, with doses, grades and cautions. On one filmed campus staircase, 64.8% of the young adults descending it did not use the rail. Nothing in a Handrail replaces medical care, and no prescribed treatment should be stopped without a clinician. (Prologue) (https://www.spiralstaircase.com/glossary/handrail) - Haplogroup: A label for one unbroken ancestral line, traced through the Y chromosome or mitochondrial DNA. It is a surname for a molecule, silent about the genes that shape digestion or metabolism. (https://www.spiralstaircase.com/glossary/haplogroup) - Heart rate variability: The beat-to-beat variation in the spacing of the pulse, tracking the vagus nerve's influence on the heart. Low values track worse health, and there is no score to hit. (https://www.spiralstaircase.com/glossary/heart-rate-variability) - Heat shock proteins: A conserved emergency response, made quickly under stress and named for the heat shock that first exposed the pattern, in fruit flies in 1962. The first edition said they protect against certain cancers; they run high in many tumors instead. Sauna raises body temperature and these proteins with it, and the sauna evidence rests largely on one Finnish cohort: no alcohol, avoid heat with unstable angina, a recent heart attack or severe aortic stenosis, and in pregnancy ask a clinician. (https://www.spiralstaircase.com/glossary/heat-shock-proteins) - Heritability: The share of variation in a trait, within one population under one set of conditions, owed to genetic differences. High heritability is compatible with a fast environmental epidemic, as myopia shows. (https://www.spiralstaircase.com/glossary/heritability) - Human milk oligosaccharides: Complex sugars in human milk that the infant cannot digest. They arrive intact in the colon and feed favored bacteria: nutrition for the baby's microbes, not the baby. (https://www.spiralstaircase.com/glossary/human-milk-oligosaccharides) - Hygiene hypothesis: David Strachan's 1989 suggestion that childhood infection carried by older siblings protects against hay fever. The label misled: what protects appears to be animals, siblings, farm dust and outdoor microbes. (https://www.spiralstaircase.com/glossary/hygiene-hypothesis) - Hyponatremia: Blood sodium at or below 135 millimoles per liter. In endurance events it comes mainly from drinking more than the body loses, and at its extreme it swells the brain. (https://www.spiralstaircase.com/glossary/hyponatremia) - Inactivity Mismatch Hypothesis: Raichlen, Pontzer and colleagues' proposal that human physiology expects the muscle work of squatting, kneeling and ground-sitting. Hadza foragers rest as long as office workers, in harder postures. (https://www.spiralstaircase.com/glossary/inactivity-mismatch-hypothesis) - Inflammatory reflex: Kevin Tracey's circuit in which the brain detects inflammation and answers down the vagus nerve, telling immune cells to quiet. An implanted stimulator built on it was approved in 2025. (https://www.spiralstaircase.com/glossary/inflammatory-reflex) - INTERSALT: A study of 10,079 adults at 52 centers worldwide, measuring sodium in 24-hour urine. Intakes ran from 0.2 millimoles a day among the Yanomami to 242 in northern China. (https://www.spiralstaircase.com/glossary/intersalt) - Ju/'hoansi: San hunter-gatherers of the Kalahari, also written !Kung, whose work diaries produced the idea of the original affluent society. Counting tool-making and housework, their weeks ran to about 40 hours for women and 45 for men. (https://www.spiralstaircase.com/glossary/ju-hoansi) - Kitava: An island in Papua New Guinea where a 1990 survey of 213 adults, by interview and resting ECG rather than autopsy or scan, found no case of stroke, sudden death or angina, although more than three-quarters of adults smoked. (https://www.spiralstaircase.com/glossary/kitava) - Lactase persistence: Keeping the milk-digesting enzyme switched on into adulthood. It arose at least four times through different mutations, long after people began consuming milk, and is absent in about two adults in three. (https://www.spiralstaircase.com/glossary/lactase-persistence) - Leaky gut: Raised permeability of the gut lining, real and measurable in celiac and inflammatory bowel disease. That restoring the barrier improves any illness is unproven, and the commercial version is weaker still. (https://www.spiralstaircase.com/glossary/leaky-gut) - LEAP trial: The randomized trial in which 640 high-risk babies ate or avoided peanut until age five. Allergy affected 17.2% of avoiders and 3.2% of eaters, and the protection held to age 12. (https://www.spiralstaircase.com/glossary/leap-trial) - Leptin: A hormone made by fat. Its main job appears to be reporting starvation rather than preventing obesity: it falls when food runs short, and blocking that fall blunts starvation's effects. (https://www.spiralstaircase.com/glossary/leptin) - Luxury trap: Yuval Noah Harari's name for the pattern in which a labor-saving technology is adopted, life expands to fill the capacity, and the technology becomes compulsory. (https://www.spiralstaircase.com/glossary/luxury-trap) - Malocclusion: Teeth that do not meet as they should: crowding, overbite, crossbite. Jaws have shortened since farming while tooth size changes only over millennia, and in animals soft food crowds teeth. (https://www.spiralstaircase.com/glossary/malocclusion) - MASLD: Metabolic dysfunction-associated steatotic liver disease, the 2023 renaming of nonalcoholic fatty liver disease. It affects about 30% of adults worldwide, and far more of them die of heart disease. (https://www.spiralstaircase.com/glossary/masld) - Mechanostat: H.M. Frost's model in which bone remodels itself to the loads placed on it, sensed by cells called osteocytes. The loop runs for life, so bone is lost within months when loading stops. (https://www.spiralstaircase.com/glossary/mechanostat) - Melanopsin: The light-sensitive pigment in a third class of retinal cells, wired to the body clock rather than to vision. It peaks near 479 nm, hence the shorthand of blue light. (https://www.spiralstaircase.com/glossary/melanopsin) - Mendelian randomization: A method using inherited genetic variants as natural instruments to test whether an exposure causes an outcome. It estimated that each extra year of education causes a myopic shift of about -0.27 diopters. (https://www.spiralstaircase.com/glossary/mendelian-randomization) - Microbiome: The microbes living in and on the body: about 38 trillion bacteria in a 70 kg reference man, nearly all in the colon and weighing about 0.2 kg in total. (https://www.spiralstaircase.com/glossary/microbiome) - Minimal shoes and barefoot walking: Footwear with little cushioning or raised heel, and going without. A 2010 study found that habitually barefoot runners landing on the forefoot produced impact peaks about three times lower than heel strikes, but a Cochrane review of 12 trials found no reduction in running injuries from any shoe type, and going shoeless or in socks indoors after 65 goes with sharply higher odds of a fall. With diabetes, numb feet, poor leg circulation or past foot ulcers, do not go barefoot or switch to minimal shoes without your clinician, and check your feet daily. (https://www.spiralstaircase.com/glossary/minimal-shoes-and-barefoot-walking) - Mismatch Card: The summary block closing most chapters, naming the system, what it expects, what it gets, what happens in the gap, the handrail and the strength of the evidence. (Prologue) (https://www.spiralstaircase.com/glossary/mismatch-card) - Myopia: Nearsightedness, produced by an eyeball grown too long. It affects 80 to 90% of school-leavers in East Asia, and outdoor time in childhood roughly halves the rate of new cases. (https://www.spiralstaircase.com/glossary/myopia) - Neolithic: The period of early farming, beginning 12,000 to 11,000 years ago. Its skeletons show, on average, shorter stature, more tooth decay and more infection than the foragers' before them. (https://www.spiralstaircase.com/glossary/neolithic) - Nociplastic pain: A third category beside pain from damaged tissue and from damaged nerves, seen in fibromyalgia and tension-type headache. It responds poorly to anti-inflammatories, opioids, surgery and injections. (https://www.spiralstaircase.com/glossary/nociplastic-pain) - Nocturnal bottleneck hypothesis: Gordon Walls's 1942 argument that mammals passed through a nocturnal phase costing them visual equipment reptiles and birds still carry. Shared gene losses support the phase; the dinosaur explanation is less secure. (https://www.spiralstaircase.com/glossary/nocturnal-bottleneck-hypothesis) - Obstetrical dilemma: Sherwood Washburn's 1960 proposal that human babies are born early because a bipedal pelvis cannot pass a finished head. A rival account puts the limit on the mother's energy supply. (https://www.spiralstaircase.com/glossary/obstetrical-dilemma) - Old friends hypothesis: Graham Rook's replacement for the hygiene hypothesis: immune regulation depends on organisms present throughout mammalian evolution, such as environmental mycobacteria, worms and lactobacilli, now largely gone from cities. (https://www.spiralstaircase.com/glossary/old-friends-hypothesis) - Orthorexia nervosa: Steven Bratman's term for a diet undertaken for health that has tightened into malnutrition or a life that no longer works. Its marker is impairment, not virtue. It is not a recognized DSM-5 diagnosis and no prevalence figure for it is established; if eating has become distressing or weight is falling, see a clinician, because this is treatable and treatment works. (https://www.spiralstaircase.com/glossary/orthorexia-nervosa) - Orthosomnia: Kelly Baron's 2017 name for patients chasing the perfect sleep score a wearable reports, trusting the device more than how they feel. (https://www.spiralstaircase.com/glossary/orthosomnia) - Ötzi: The Iceman, found in the Alps in 1991, dead between 3350 and 3120 BCE with whipworm, worn joints, calcified arteries and genetic risk for type 2 diabetes. (https://www.spiralstaircase.com/glossary/otzi) - Paleolithic: The long stretch of human prehistory before farming. This book uses it for chronology, not as a menu: Marlene Zuk's objection is that no single ancestral environment existed. (https://www.spiralstaircase.com/glossary/paleolithic) - Persistence hunting: Running or walking prey to exhaustion in the heat. Louis Liebenberg documented 10 in the central Kalahari, and historical accounts show the tactic was widespread, not that it was common. (https://www.spiralstaircase.com/glossary/persistence-hunting) - Peto's paradox: The puzzle that animals with a thousand times more cells than humans do not get proportionally more cancer. African elephants carry at least 20 copies of the tumor suppressor TP53. (https://www.spiralstaircase.com/glossary/petos-paradox) - PFAS: Per- and polyfluoroalkyl substances, industrial chemicals the liver cannot break down. In Ronneby, Sweden, half of residents' PFOA cleared in 2.7 years, half the PFHxS in 5.3. (https://www.spiralstaircase.com/glossary/pfas) - Polygenic risk score: A score summing many gene variants of tiny individual effect. It shifts a probability rather than making a diagnosis, and works less well in ancestries thinly represented in its training data. (https://www.spiralstaircase.com/glossary/polygenic-risk-score) - Polyvagal theory: Stephen Porges's account of a distinct vagal circuit producing a calm-and-connect state. A 2023 critique argues its premises are unsupported; the nerve still matters, and the two claims are separate. (https://www.spiralstaircase.com/glossary/polyvagal-theory) - Prediction error: The signal dopamine neurons carry: a burst when a reward beats prediction, baseline when it matches, a dip when it fails to come. Addictive drugs bypass the comparison. (https://www.spiralstaircase.com/glossary/prediction-error) - Rarámuri: Also called Tarahumara, farmers and runners of Chihuahua, Mexico. Researchers working with them named the popular romance the "fallacy of the athletic savage": they get injured too, and mostly they walk. (https://www.spiralstaircase.com/glossary/raramuri) - Regulatory T cells: Immune cells that damp down immune responses, controlled by the gene FOXP3. Their discovery won the 2025 Nobel Prize, and the Nobel Assembly called them the immune system's security guards. (https://www.spiralstaircase.com/glossary/regulatory-t-cells) - Resonant breathing: Slow breathing at roughly five to six breaths a minute, the pace at which breath-linked swings in heart rate grow largest. The Ave Maria in Latin sets almost exactly that pace. It sits alongside care for asthma, high blood pressure, anxiety and depression and never in place of it. Hyperventilation and breath-holds are a separate practice, for dry land only and never in or near water. (https://www.spiralstaircase.com/glossary/resonant-breathing) - Risky play: Ellen Sandseter's six categories of the trouble children seek out: heights, speed, dangerous tools, dangerous elements, rough-and-tumble, and going off alone. Meeting fear in chosen doses may be how they tune it. Open water, traffic and firearms are not risky play; they are risks, and the ordinary precautions apply. (https://www.spiralstaircase.com/glossary/risky-play) - Sarcopenia: The age-related loss of muscle mass and strength, now screened for with grip strength or gait speed: what a muscle can do predicts falls and death better than its bulk. (https://www.spiralstaircase.com/glossary/sarcopenia) - Sedentary behavior: Waking time spent sitting, reclining or lying at a low energy cost. It differs from physical inactivity, meaning too little activity to meet the guidelines; a person can be both. (https://www.spiralstaircase.com/glossary/sedentary-behavior) - Senescence, cellular: The state of a cell that is alive and busy but permanently out of the division business. Such cells secrete inflammatory signals, and in quantity they feed the chronic inflammation of aging. (https://www.spiralstaircase.com/glossary/senescence-cellular) - Sickle cell trait: Carrying one copy of the sickle hemoglobin allele protects against severe malaria; two copies cause sickle cell disease. It is the standard example of a trade-off rather than a mismatch. (https://www.spiralstaircase.com/glossary/sickle-cell-trait) - Sickness behavior: The lethargy, low mood and lost appetite that travel with fever, argued in 1988 to be an organized strategy rather than debilitation. Mice have neurons that control fever and appetite together. (https://www.spiralstaircase.com/glossary/sickness-behavior) - Sitting-rising test: Sitting on the floor and standing up again, scored from 10 with a point lost for each hand or knee used. The lowest scorers had 5.44 times the mortality of the highest. Try it with something sturdy within reach if your balance is uncertain, and read a low score as a prompt to train, not as a prognosis. (https://www.spiralstaircase.com/glossary/sitting-rising-test) - Sleep Regularity Index: A measure of how consistent sleep timing is from night to night. Across nearly 61,000 accelerometer-wearing adults it predicted death better than sleep duration did. (https://www.spiralstaircase.com/glossary/sleep-regularity-index) - Smoke detector principle: Randolph Nesse's explanation for why defenses such as fever, pain and anxiety fire on many false alarms: when the response is cheap and missing a threat is fatal, selection sets the threshold low. (https://www.spiralstaircase.com/glossary/smoke-detector-principle) - Social brain hypothesis: Robin Dunbar's 1998 argument that primate brains grew to manage social relationships. Diet, ecological problem-solving and the storage of learned culture are live rivals; no single pressure has won. (https://www.spiralstaircase.com/glossary/social-brain-hypothesis) - Social isolation: The objective state of having few contacts, distinct from loneliness, the felt lack of the connection you want. Pooled studies link isolation to 29% higher odds of dying during follow-up. (https://www.spiralstaircase.com/glossary/social-isolation) - Social jetlag: The gap between the sleep timing a person's clock wants and the timing work and school impose, paid back at weekends. It tracks higher body mass index. (https://www.spiralstaircase.com/glossary/social-jetlag) - Social prescribing: Referral by a health service to choirs, walking groups, gardening or volunteering rather than to a prescription pad. England has employed link workers since 2019, and whether the programme improves health outcomes is still an open question. (https://www.spiralstaircase.com/glossary/social-prescribing) - Supernormal stimulus: An exaggerated version of a natural signal that draws a stronger response than the real thing, such as the oversized model egg an oystercatcher prefers to her own. (https://www.spiralstaircase.com/glossary/supernormal-stimulus) - Systemic chronic inflammation: Low-grade inflammation running for years with no infection to justify it, proposed in 2019 as a shared thread through cardiovascular disease, cancer, diabetes and much else. It is a hub, not a root. (https://www.spiralstaircase.com/glossary/systemic-chronic-inflammation) - Telomere: The repeated cap of DNA and protein at the end of a chromosome, shortening with each cell division. Shorter telomeres in immune cells are associated with higher reported stress. (https://www.spiralstaircase.com/glossary/telomere) - Thermoneutral zone: The band in which the body holds core temperature by adjusting skin blood flow alone, without shivering or sweating: roughly 15 to 25°C (59 to 77°F) for a clothed adult at office work. (https://www.spiralstaircase.com/glossary/thermoneutral-zone) - Thrifty genotype hypothesis: James Neel's 1962 proposal that genes favoring efficient fat storage were selected by famine and turned harmful with plenty. Famine comparisons and most selection scans go against it, though a Samoan variant of CREBRF is a real exception, and a 2024 review calls the question unresolved. (https://www.spiralstaircase.com/glossary/thrifty-genotype-hypothesis) - Time-restricted eating: Confining meals to a fixed daily window. In two randomized trials it added no weight loss beyond the calorie awareness that came with it: a tool rather than a mechanism. Skip it in pregnancy or with a history of disordered eating, and never begin one while taking glucose-lowering medication without your clinician's adjustment, because of the risk of hypoglycemia. (https://www.spiralstaircase.com/glossary/time-restricted-eating) - Trier Social Stress Test: A 1993 laboratory procedure: 10 minutes of dread, then a mock job talk and serial subtraction before judges. It raises saliva cortisol two to three fold in roughly 70% to 80% of people. (https://www.spiralstaircase.com/glossary/trier-social-stress-test) - Tsimane: Forager-horticulturalists of the Bolivian Amazon, with the lowest coronary artery calcium reported anywhere. They also report chronic pain at industrialized rates, so this book uses them as evidence both ways. (https://www.spiralstaircase.com/glossary/tsimane) - Turkana: Pastoralists of northwest Kenya who get about 62% of their calories from milk. In one large study no traditional Turkana met the criteria for obesity or metabolic syndrome. (https://www.spiralstaircase.com/glossary/turkana) - Ultra-processed food: The NOVA classification's term for industrial assemblies of substances extracted from foods, marked by ingredients never or rarely used in kitchens. Such food supplies 55% of American calories. (https://www.spiralstaircase.com/glossary/ultra-processed-food) - Umami: The savory taste of amino acids, named by Kikunae Ikeda in 1908 after he isolated monosodium glutamate from kombu. Its receptor shares a protein with the sweet receptor. (https://www.spiralstaircase.com/glossary/umami) - Vagus nerve: The longest cranial nerve, running from the brainstem to heart, lungs, gut, liver and spleen, and the main channel of the parasympathetic nervous system. It carries traffic both ways, as the inflammatory reflex shows. (https://www.spiralstaircase.com/glossary/vagus-nerve) - VILPA: Vigorous intermittent lifestyle physical activity: short bursts of hard effort folded into ordinary life, such as stairs taken fast. A median of 4.4 minutes a day tracked about 26% to 30% lower mortality. (https://www.spiralstaircase.com/glossary/vilpa) - Vitamin D: The vitamin the skin makes when ultraviolet B light strikes a cholesterol-like molecule, a process melanin slows without stopping. It prevents rickets; in large trials, supplements did not prevent cancer, fractures or heart disease. (https://www.spiralstaircase.com/glossary/vitamin-d) - VO2 max: The most oxygen the body can use at full effort. This aerobic ceiling falls 3 to 6% per decade in the 20s and 30s and more than 20% per decade from the 70s. (https://www.spiralstaircase.com/glossary/vo2-max) - Yanomami: A people of Venezuela and Brazil whose systolic blood pressure showed no measurable rise with age, and whose sodium intake was the lowest in INTERSALT. (https://www.spiralstaircase.com/glossary/yanomami)