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Chapter 9 of the book

Heat and Cold

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.3 things to start with3 popular claims graded58 works cited

How the chapter opens

Off the Korean island of Jeju, women called haenyeo have dived for shellfish and seaweed for centuries, and until wetsuits arrived they did it through the winter in suits of thin cotton. In the early sixties a team of physiologists led by Suk-Ki Hong went out to measure them. In winter water around 50°F her oral temperature fell to about 91°F within a quarter of an hour. Then they measured the women's energy use at complete rest. In non-diving women from the same community it stayed flat all year. In the divers it climbed with the seasons, from a little above the standard in summer to about a third above it in winter. The team called this "cold adaptation, induced by repeated immersion in cold water."1

In the late seventies the divers switched to wetsuits, and nobody planned the experiment that followed. A second team came back with the same methods and found the winter rise gone. Within three to five years every measure of the adaptation had faded, from resting metabolism to the water temperature that set off shivering. The adaptation was real, measurable and rented. What survives in the oldest haenyeo fits the story: they keep some cold tolerance in the face and hands, the parts a wetsuit leaves bare.2

What the chapter covers

The argument, the studies and the stories are in the book. Get the book.

  • ·What Your Body Expects
  • ·What It Gets Instead
  • ·Cold, Sized Honestly
  • ·Heat, and the Body From Inside

Mismatch card

The 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 (EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested. to ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.)

Strength of evidence

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials. 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.

What you've heard

Popular claims this chapter tests, each with the book's verdict and grade.

The protocol

Each action carries the book's evidence grade. How the grades work.

Start here

  1. Let your home move a little: cooler rooms in winter, and a bedroom that cools at night

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    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.20

  2. End your shower with thirty seconds of cold, if you like it and your heart is healthy

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.for fewer sick daysEmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.for anything else

    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.

  3. Heat: a sauna or a hot bath, a few times a week, if you have access and enjoy it

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    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).21 Why: two large cohorts link regular heat with fewer heart deaths (that link is ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.; 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.

Then, pick from this menu

  • **In a heat wave, find cool air for the hottest hours (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.).** Spend them somewhere air-conditioned if your home is not. Heat tolerance comes from repeated exposure, so build up warm-weather activity over days rather than all at once. In humid heat, slow down, drink, and stop early.

  • **Open cold water, gradually and never alone (EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested. for benefit).** Enter slowly, keep your face clear, and float on your back until the gasping settles, about a minute to a minute and a half. The response fades after about four dips. Get out before shivering is strong.

  • **Keep cold water away from strength sessions (ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.).** Cold water straight after lifting blunts muscle growth, and usually strength gains, in small trials. Several hours apart, or on a non-lifting day, is the cautious reading (Chapter 4).22

  • **Take control of your corner at work (EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.).** A layer you can remove, a desk fan in summer, or a request for a degree or two warmer.

If this is you

Perimenopause and after, with hot flushes

use fans, layers and a cool bedroom for comfort, not as treatment. If flushes bother you, see a clinician: hormone therapy is the most effective treatment, and cognitive behavioral therapy and several non-hormonal prescriptions also have trial support (StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.). Details are in Chapter 15.

Older, or with a heart condition

ask a clinician before starting sauna or cold water. In winter, warm the bathroom before a hot bath, keep soaks moderate, and stand up slowly.

Older, with heart disease, or taking water pills or other drugs that affect sweating or fluid balance, in a heat wave

you are at higher risk. Plan your cool place before the heat arrives, and do not exercise hard in humid heat.

Pregnant

ask your own clinician before using a sauna or hot tub. The evidence on heat in early pregnancy conflicts.

Tight budget

cool rooms and cold showers cost nothing, and a hot bath stands in for a sauna.

Short on time

the cold finish adds thirty seconds to a shower you were taking anyway.

Safety

Cold water kills through cold shock, not slow chilling; never swim in cold open water alone, and skip alcohol near any water. Alcohol was involved in half of Finnish sauna deaths. Avoid saunas with unstable angina, a recent heart attack or severe aortic stenosis. In Japan, estimates run to well over ten thousand bath deaths a year, mostly older people in winter, when a cold dressing room raises blood pressure and a long hot soak then drops it; warm the bathroom to at least 68°F first.23 None of this replaces treatment for any condition.

The skeptic's box

What could overturn this chapter, from the chapter itself.

The sauna story rests almost entirely on one Finnish cohort of men, analyzed again and again by one research group. Its comparison group is men who took a sauna once a week, not never, and only about two hundred men sat in the top group. Letters in reply ran under the title "The link between sauna bathing and mortality may be noncausal."24 The Japanese bathing study is independent support, and also observational.

The cold-shower trial was unblinded and counted days absent, not days ill. The trials that trained brown fat were tiny, and pooled studies of cold found no change in fasting blood sugar, insulin or triglycerides.

The strongest objection is simpler: the thermal bubble saves lives. Cold still kills far more people than heat, and air conditioning is why hot days no longer kill Americans as they once did. Nothing here argues for a cold house. What would change the picture is a trial of regular sauna or mild cold that counts heart attacks and deaths, and the Finnish findings repeated in women and outside Finland.

Go deeper in the reference library

The research this chapter was built from, as longer reference entries: each with its own mismatch card, graded recommendations and the case against it.

See also in the book

Sources behind this page

  1. 1.Hong, S.K., Rahn, H., Kang, D.H., Song, S.H., and Kang, B.S. (1963). "Diving pattern, lung volumes, and alveolar gas of the Korean diving woman (ama)." Journal of Applied Physiology, 18(3), 457-465. https://doi.org/10.1152/jappl.1963.18.3.457 ; Kang, B.S., Song, S.H., Suh, C.S., and Hong, S.K. (1963). "Changes in body temperature and basal metabolic rate of the ama." Journal of Applied Physiology, 18(3), 483-488. https://doi.org/10.1152/jappl.1963.18.3.483 (oral temperature 33°C after about 15 minutes in 10°C winter water; typical dive 30 seconds, about 60 an hour; basal metabolic rate about 5% above the DuBois standard in summer and 35% in winter) ; Lee, J.Y., Park, J., and Kim, S. (2017). "Cold adaptation, aging, and Korean women divers haenyeo." Journal of Physiological Anthropology, 36(1), 33. https://doi.org/10.1186/s40101-017-0146-6 (cotton suits about 0.5 mm thick until the late 1970s)
  2. 2.Park, Y.S., Rennie, D.W., Lee, I.S., Park, Y.D., et al. (1983). "Time course of deacclimatization to cold water immersion in Korean women divers." Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, 54(6), 1708-1716. https://doi.org/10.1152/jappl.1983.54.6.1708 (wetsuits worn since 1977; metabolism and insulation faded in about three years, finger blood flow in four, the shivering threshold in five) ; Lee, J.Y., Park, J., and Kim, S. (2017). "Cold adaptation, aging, and Korean women divers haenyeo." Journal of Physiological Anthropology, 36(1), 33. https://doi.org/10.1186/s40101-017-0146-6 (older divers retain local cold tolerance in the extremities)
  3. 24.Kivimäki, M., Virtanen, M., and Ferrie, J.E. (2015). "The link between sauna bathing and mortality may be noncausal." JAMA Internal Medicine, 175(10), 1718-1719. https://doi.org/10.1001/jamainternmed.2015.3426
  4. 12.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)
  5. 14.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)
  6. 18.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)
  7. 20.World Health Organization (2018). WHO Housing and Health Guidelines, chapter "Low indoor temperatures and insulation." Geneva: WHO. https://www.ncbi.nlm.nih.gov/books/NBK535294/ (18°C; a strong recommendation for temperate and colder climates). The 18-19°C (64-66°F) winter setting rests on the small trials in note 11.
  8. 21.Haghayegh, S., Khoshnevis, S., Smolensky, M.H., Diller, K.R., and Castriotta, R.J. (2019). "Before-bedtime passive body heating by warm shower or bath to improve sleep: a systematic review and meta-analysis." Sleep Medicine Reviews, 46, 124-135. https://doi.org/10.1016/j.smrv.2019.04.008 (water at 40-42.5°C, one to two hours before bed)
  9. 23.Kenttämies, A., and Karkola, K. (2008). "Death in sauna." Journal of Forensic Sciences, 53(3), 724-729. https://doi.org/10.1111/j.1556-4029.2008.00703.x (Finland, 1990-2002; 50% of cases involved alcohol); Hannuksela, M.L., and Ellahham, S. (2001). "Benefits and risks of sauna bathing." American Journal of Medicine, 110(2), 118-126. https://doi.org/10.1016/s0002-9343(00)00671-9 ; Milunsky, A., Ulcickas, M., Rothman, K.J., Willett, W., et al. (1992). "Maternal heat exposure and neural tube defects." JAMA, 268(7), 882-885. https://pubmed.ncbi.nlm.nih.gov/1640616/ ; Saxén, L., Holmberg, P.C., Nurminen, M., and Kuosma, E. (1982). "Sauna and congenital defects." Teratology, 25(3), 309-313. https://doi.org/10.1002/tera.1420250307 ; Tochihara, Y. (2022). "A review of Japanese-style bathing: its demerits and merits." Journal of Physiological Anthropology, 41(1), 5. https://doi.org/10.1186/s40101-022-00278-0 (about 19,000 deaths a year; bathroom at 20°C or higher); Suzuki, M., Shimbo, T., Ikaga, T., and Hori, S. (2017). "Sudden death phenomenon while bathing in Japan: mortality data." Circulation Journal, 81(8), 1144-1149. https://doi.org/10.1253/circj.CJ-16-1066 (13,369 in the six months from October); Tochihara, Y., Hashiguchi, N., and Loh, P.Y. (2026). "Why do many elderly Japanese die suddenly during winter bathing?" International Journal of Biometeorology, 70(4), 126. https://doi.org/10.1007/s00484-025-03086-0 ; Centers for Disease Control and Prevention (2024). Risk factors for drowning. https://www.cdc.gov/drowning/risk-factors/index.html
  10. 22.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 ; 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

Every work this chapter cites

The chapter's 24 notes cite 58 works, listed by note number. Each is also in the full source register.

  1. 1.Hong, S.K., Rahn, H., Kang, D.H., Song, S.H., and Kang, B.S (1963). Diving pattern, lung volumes, and alveolar gas of the Korean diving woman (ama). Journal of Applied Physiology. 10.1152/jappl.1963.18.3.457Kang, B.S., Song, S.H., Suh, C.S., and Hong, S.K (1963). Changes in body temperature and basal metabolic rate of the ama. Journal of Applied Physiology. 10.1152/jappl.1963.18.3.483Lee, J.Y., Park, J., and Kim, S (2017). Cold adaptation, aging, and Korean women divers haenyeo. Journal of Physiological Anthropology. 10.1186/s40101-017-0146-6
  2. 2.Park, Y.S., Rennie, D.W., Lee, I.S., Park, Y.D., et al (1983). Time course of deacclimatization to cold water immersion in Korean women divers. Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology. 10.1152/jappl.1983.54.6.1708Lee, J.Y., Park, J., and Kim, S (2017). Cold adaptation, aging, and Korean women divers haenyeo. Journal of Physiological Anthropology. 10.1186/s40101-017-0146-6
  3. 3.Darwin, C (1845). Journal of Researches into the Natural History and Geology of the Countries Visited during the Voyage of H.M.S. Beagle Round the World. gutenberg.orgHill, R.W (2023). Living naked in the cold: new insights into metabolic feasibility in primeval cultures. BioScience. 10.1093/biosci/biad002
  4. 4.Kingma, B.R., Frijns, A.J., Schellen, L., and van Marken Lichtenbelt, W.D (2014). Beyond the classic thermoneutral zone: including thermal comfort. Temperature. 10.4161/temp.29702Yetish, G., Kaplan, H., Gurven, M., Wood, B., et al (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 10.1016/j.cub.2015.09.046
  5. 5.Périard, J.D., Racinais, S., and Sawka, M.N (2015). Adaptations and mechanisms of human heat acclimation: applications for competitive athletes and sports. Scandinavian Journal of Medicine and Science in Sports. 10.1111/sms.12408Lieberman, D.E (2015). Human locomotion and heat loss: an evolutionary perspective. Comprehensive Physiology. 10.1002/cphy.c140011Kamberov, Y.G., Guhan, S.M., DeMarchis, A., Jiang, J., et al (2018). Comparative evidence for the independent evolution of hair and sweat gland traits in primates. Journal of Human Evolution. 10.1016/j.jhevol.2018.10.008
  6. 6.Yamada, Y., Zhang, X., Henderson, M.E.T., Sagayama, H., et al (2022). Variation in human water turnover associated with environmental and lifestyle factors. Science. 10.1126/science.abm8668Johnson, F., Mavrogianni, A., Ucci, M., Vidal-Puig, A., and Wardle, J (2011). Could increased time spent in a thermal comfort zone contribute to population increases in obesity? Obesity Reviews. 10.1111/j.1467-789X.2010.00851.x
  7. 7.Leong, D.P., Teo, K.K., Rangarajan, S., Lopez-Jaramillo, P., et al (2015). Prognostic value of grip strength: findings from the Prospective Urban Rural Epidemiology (PURE) study. The Lancet. 10.1016/S0140-6736(14Zhao, Q., Guo, Y., Ye, T., Gasparrini, A., et al (2021). Global, regional, and national burden of mortality associated with non-optimal ambient temperatures from 2000 to 2019. Lancet Planetary Health. 10.1016/S2542-5196(21Barreca, A., Clay, K., Deschenes, O., Greenstone, M., and Shapiro, J.S (2016). Adapting to climate change: the remarkable decline in the US temperature-mortality relationship over the twentieth century. Journal of Political Economy. 10.1086/684582Ballester, J., Quijal-Zamorano, M., Méndez Turrubiates, R.F., Pegenaute, F., et al (2023). Heat-related mortality in Europe during the summer of 2022. Nature Medicine. 10.1038/s41591-023-02419-z
  8. 8.Vecellio, D.J., Wolf, S.T., Cottle, R.M., and Kenney, W.L (2022). Evaluating the 35°C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project). Journal of Applied Physiology. 10.1152/japplphysiol.00738.2021Périard, J.D., Racinais, S., and Sawka, M.N (2015). , as note 5.
  9. 9.Kingma, B., and van Marken Lichtenbelt, W (2015). Energy consumption in buildings and female thermal demand. Nature Climate Change. 10.1038/nclimate2741Karjalainen, S (2012). Thermal comfort and gender: a literature review. Indoor Air. 10.1111/j.1600-0668.2011.00747.xREMI Network (2015). ASHRAE rebuts new thermal comfort research. reminetwork.com
  10. 10.Cohade, C., Mourtzikos, K.A., and Wahl, R.L (2003). 'USA-Fat': prevalence is related to ambient outdoor temperature. Journal of Nuclear Medicine. pubmed.ncbi.nlm.nih.govCohade, C., Osman, M., Pannu, H.K., and Wahl, R.L (2003). Uptake in supraclavicular area fat ('USA-Fat'): description on 18F-FDG PET/CT. Journal of Nuclear Medicine. 10.1007/s00259-002-0902-6
  11. 11.Yoneshiro, T., Aita, S., Matsushita, M., Kayahara, T., et al (2013). Recruited brown adipose tissue as an antiobesity agent in humans. Journal of Clinical Invest. 10.1172/JCI67803Lee, P., Smith, S., Linderman, J., Courville, A.B., et al (2014). Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans. Diabetes. 10.2337/db14-0513Hanssen, M.J., Hoeks, J., Brans, B., van der Lans, A.A., et al (2015). Short-term cold acclimation improves insulin sensitivity in patients with type 2 diabetes mellitus. Nature Medicine. 10.1038/nm.3891van Beek, S., Hashim, D., Bengtsson, T., and Hoeks, J (2023). Physiological and molecular mechanisms of cold-induced improvements in glucose homeostasis in humans. International Journal of Obesity. 10.1038/s41366-023-01270-z
  12. 12.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. 10.2967/jnumed.112.111336Tabei, 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. 10.3390/biomedicines12030537Becher, T., Palanisamy, S., Kramer, D.J., Eljalby, M., et al (2021). Brown adipose tissue is associated with cardiometabolic health. Nature Medicine. 10.1038/s41591-020-1126-7
  13. 13.Buijze, G.A., Sierevelt, I.N., van der Heijden, B.C., Dijkgraaf, M.G., and Frings-Dresen, M.H (2016). The effect of cold showering on health and work: a randomized controlled trial. PLoS ONE. 10.1371/journal.pone.0161749Cain, T., Brinsley, J., Bennett, H., Nelson, M., et al (2025). Effects of cold-water immersion on health and wellbeing: a systematic review and meta-analysis. PLoS ONE. 10.1371/journal.pone.0317615
  14. 14.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. 10.1007/s004210050065
  15. 15.Tipton, M.J (1989). The initial responses to cold-water immersion in man. Clinical Science. 10.1042/cs0770581Tipton, M (2022). Float to live. port.ac.ukBarwood, M.J., Eglin, C., Hills, S.P., Johnston, N., et al (2024). Habituation of the cold shock response: a systematic review and meta-analysis. Journal of Thermal Biology. 10.1016/j.jtherbio.2023.103775
  16. 16.Laukkanen, T., Khan, H., Zaccardi, F., and Laukkanen, J.A (2015). Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. 10.1001/jamainternmed.2014.8187Ukai, T., Iso, H., Yamagishi, K., Saito, I., et al (2020). Habitual tub bathing and risks of incident coronary heart disease and stroke. Heart. 10.1136/heartjnl-2019-315752
  17. 17.Brunt, V.E., Howard, M.J., Francisco, M.A., Ely, B.R., and Minson, C.T (2016). Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. Journal of Physiology. 10.1113/JP272453Lee, E., Kolunsarka, I., Kostensalo, J., Ahtiainen, J.P., et al (2022). Effects of regular sauna bathing in conjunction with exercise on cardiovascular function: a multi-arm, randomized controlled trial. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. 10.1152/ajpregu.00076.2022Debray, A., Gravel, H., Garceau, L., Bartlett, A.A., et al (2023). Finnish sauna bathing and vascular health of adults with coronary artery disease: a randomized controlled trial. Journal of Applied Physiology. 10.1152/japplphysiol.00322.2023Kaiser, B.W., Comrada, L.N., Gibson, B.M., Reed, E.L., et al (2025). No effect of either heat therapy or aerobic exercise training on blood pressure in adults with untreated hypertension: a randomized clinical trial. Journal of Applied Physiology. 10.1152/japplphysiol.00959.2024
  18. 18.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. 10.1016/j.xcrm.2021.100408
  19. 19.The North American Menopause Society 2023 Nonhormone Therapy Position Statement Advisory Panel (2023). The 2023 nonhormone therapy position statement of The North American Menopause Society. Menopause. 10.1097/GME.0000000000002200McCurry, S.M., Guthrie, K.A., Morin, C.M., Woods, N.F., et al (2016). Telephone-based cognitive behavioral therapy for insomnia in perimenopausal and postmenopausal women with vasomotor symptoms: a MsFLASH randomized clinical trial. JAMA Internal Medicine. 10.1001/jamainternmed.2016.1795
  20. 20.World Health Organization (2018). WHO Housing and Health Guidelines. ncbi.nlm.nih.gov
  21. 21.Haghayegh, S., Khoshnevis, S., Smolensky, M.H., Diller, K.R., and Castriotta, R.J (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep: a systematic review and meta-analysis. Sleep Medicine Reviews. 10.1016/j.smrv.2019.04.008
  22. 22.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. 10.1007/s40279-020-01362-0Piñero, 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. 10.1002/ejsc.12074
  23. 23.Kenttämies, A., and Karkola, K (2008). Death in sauna. Journal of Forensic Sciences. 10.1111/j.1556-4029.2008.00703.xHannuksela, M.L., and Ellahham, S (2001). Benefits and risks of sauna bathing. American Journal of Medicine. 10.1016/s0002-9343(00Milunsky, A., Ulcickas, M., Rothman, K.J., Willett, W., et al (1992). Maternal heat exposure and neural tube defects. JAMA. 10.1002/tera.1420250307Tochihara, Y (2022). A review of Japanese-style bathing: its demerits and merits. Journal of Physiological Anthropology. 10.1186/s40101-022-00278-0Suzuki, M., Shimbo, T., Ikaga, T., and Hori, S (2017). Sudden death phenomenon while bathing in Japan: mortality data. Circulation Journal. 10.1253/circj.CJ-16-1066Tochihara, Y., Hashiguchi, N., and Loh, P.Y (2026). Why do many elderly Japanese die suddenly during winter bathing? International Journal of Biometeorology. 10.1007/s00484-025-03086-0Centers for Disease Control and Prevention (2024). Risk factors for drowning. cdc.gov
  24. 24.Kivimäki, M., Virtanen, M., and Ferrie, J.E (2015). The link between sauna bathing and mortality may be noncausal. JAMA Internal Medicine. 10.1001/jamainternmed.2015.3426

The full source register

This page carries the chapter's apparatus. The chapter itself, and the fifteen others, are in the book.

Get the bookThe 30-day protocolAll sixteen chapters