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The chapters, start-here actions, graded claims and reference topics on sleep and light.

The chapters, start-here actions, graded claims and reference topics on movement.

The chapters, start-here actions, graded claims and reference topics on strength and bone.

The chapters, start-here actions, graded claims and reference topics on food.

The chapters, start-here actions, graded claims and reference topics on the gut and immunity.

The chapters, start-here actions, graded claims and reference topics on cold and heat.

The chapters, start-here actions, graded claims and reference topics on stress and the mind.

The chapters, start-here actions, graded claims and reference topics on people and loneliness.

The chapters, start-here actions, graded claims and reference topics on phones and attention.

The chapters, start-here actions, graded claims and reference topics on women's health.

The chapters, start-here actions, graded claims and reference topics on men's health.

The chapters, start-here actions, graded claims and reference topics on aging.

Every mismatch card in one table: what each system expects, what it gets now, the gap and the grade.

The Hadza, Tsimane, Ju/'hoansi, Turkana and others, quoted from the book and its library.

The two glossary definitions, side by side.

Thousands of older American women in the Women's Health Study once agreed to wear a small motion sensor through the waking hours of a single week....

In 1911 Ethel Margaret Burnside, Hertfordshire's first "chief health visitor and lady inspector of midwives," set up "an army of trained nurses" and...

In the years after the Second World War, a London double-decker bus carried two employees and, without anyone planning it, an experiment. The driver...

The women in the trial had the kind of bones that make doctors careful. All of them, about a hundred in total, were past menopause, and all had low...

In 1963 a government survey of arthritis among the Pima of the Gila River Indian Community, in southern Arizona, "unexpectedly revealed that many...

On paper, the Amish and the Hutterites look like the same experiment run twice. Both sects arose in Reformation Europe and later crossed to America.

In July 1962 a 23-year-old French geologist named Michel Siffre climbed down into a cave in the Alps to live beside an underground glacier.

Researchers once asked people in three foraging societies with no electric light to wear a small monitor on the wrist through the night: the Hadza of...

Off the Korean island of Jeju, women called haenyeo have dived for shellfish and seaweed for centuries, and until wetsuits arrived they did it...

In 2002 a metallic green beetle from East Asia was identified as the reason ash trees were dying in Detroit and in Windsor, Ontario. The emerald ash...

Roseto, Pennsylvania, should not have been unusual. The Italian-American town sat a short drive from Bangor and Nazareth, in the same corner of the...

In 2025 researchers reported a trial in which Turkish high-school students did their math practice with an AI beside them.

At Britain's Common Cold Unit in Salisbury, volunteers came to catch colds on purpose. They lived in flats, alone or in twos and threes, and could...

In 1970 and 1971, as Army enlisted men left Vietnam, the military tested their urine for opiates on the way out, and almost eleven in every hundred...

Every night for two years in the late 1980s, the anthropologist Beverly Strassmann noted which women were sleeping at the two menstrual huts of...

When researchers came to scan their hearts, about sixteen thousand Tsimane lived along the Maniqui River, a tributary of the Amazon in lowland...

Against, as stated. A systematic review of randomized trials found that linoleic acid, the omega-6 fat plentiful in seed oils, had no significant...

Against, and the risk is measured. Unpasteurized milk and cheese are eaten by a small minority of Americans, yet they accounted for 96% of the...

Emerging and contested. Skin contact with the earth is said to transfer electrons and reduce inflammation. The idea rests on reviews written by its...

Self-reported only, no trials. In a large survey of adults on the diet, nearly all reported better health. There was no control group, the...

Unsupported, with a safety catch. In a systematic review of ten small studies, two showed some improvement in apnea measures and the rest none, and...

Probable for foot strength; unsupported for injury prevention. Eight weeks of walking in minimal shoes increased foot muscle size and strength in...

A narrow effect on heat regulation; nothing on fat loss. Eight Scandinavian winter swimmers, compared with eight controls, regulated body heat...

Against: the one trial runs the other way. An Australian trial assigned adults to use sunscreen daily or at their own discretion. Over long follow-up...

Unsupported. No controlled trial shows that these products improve on what a working liver and kidneys already do. With no primary studies to check,...

Exaggerated about tenfold. Break up sitting, but above all, move more. Long sitting is linked to higher death rates, but the comparison with...

A round number, not a threshold. The number has no documented scientific origin, and the usual story of where it came from traces to no primary...

Wrong if building muscle is the goal. For strength training, the evidence points the other way. In a three-month trial, active men lifted twice a...

False. Past a point, extra protein stops adding muscle. In pooled trials, protein supplements added modestly to the strength and muscle that training...

No evidence of benefit for people without diabetes. A curiosity, not a health tool, and no substitute for a blood test. The first over-the-counter...

False as a rule. Drink to thirst, more in heat and hard exercise, and never past thirst in long events. The rule seems to have grown from a 1945 US...

For healthy people, unsupported; spend the money on yogurt and beans. In a review of seven randomized trials, probiotic supplements did not change...

Expensive vitamins, and no substitute for vegetables. The best evidence is a systematic review of commercial mixed fruit and vegetable concentrates....

Real in specific diseases, unproven as an everyday diagnosis. How easily things slip through the gut lining can be measured, and that leakiness does...

Mostly unsupported; skip the glasses unless a clinician suggests them for a specific sleep problem. A Cochrane review found that blue-filtering...

Right direction, invented number. Get outside early, and stay longer when it is gray. No study has tested ten minutes. The clock's response is steep...

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. The...

Unproven. The juice adds sugar, and magnesium is a long shot, not a treatment. Tart cherries contain melatonin, but far less than a low-dose pill....

A pleasant way to rest, not a substitute for sleep. Guided rest practices such as yoga nidra, and the related practice sold as non-sleep deep rest,...

Oversold. Mild cold may nudge insulin sensitivity in tiny trials, but it will not move your weight. Brown fat does switch on in the cold, and a few...

A real number, misapplied. Enjoy the jolt if you like it, without expecting a chemical dose. The figure comes from a laboratory study of young men...

Not a protocol. 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...

Enjoy the forest as relaxation, plausible though the size is uncertain; the tree-chemical immune story is unproven. The chemical story traces to one...

A planned break brings a small lift and can reset a habit; "resets your brain" is overstated. The best trial, the four weeks off Facebook, found a...

Unproven as stated, with a serious case on both sides; heavy use is a fair worry, and the causal claim is open. The rise in teenage depression,...

False. If you are exhausted, see a clinician rather than the supplement aisle. A systematic review found "no substantiation that 'adrenal fatigue' is...

A reasonable quick reset with thin evidence; "fastest" and "proven" are overstated. The claim rests on one trial. It randomly assigned about a...

Helps a little; not a substitute for therapy or medication. Pooled across randomized trials, breathwork brought small-to-moderate reductions in...

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...

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. In...

Not supported. Train consistently and adjust on days you feel bad, whatever the reason. The idea turns a real fact, that hormones swing across the...

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...

False. Levels drift down slowly, and partly with weight and health, and only a minority of men meet the diagnosis of symptoms plus repeated low...

Not reliable for individuals. Cells tag their DNA with small chemical marks, and the tags at a few hundred sites predict a person's age across almost...

Unsupported so far. Supplements called NR and NMN reliably raise blood levels of NAD+, a molecule cells use to handle energy. The trouble is what...

In 1966, five healthy young men in Dallas spent three weeks in bed. When they got up, they had lost more aerobic fitness than the next three decades...

The study began with an extracted tooth. Pam Gill, of the University of Bristol, recalled that a colleague had a tooth removed and wanted it X-rayed,...

On 29 August 1990, in the central Kalahari of Botswana, four !Xo and /Gwi hunters (the ! and / mark click consonants) from Lone Tree chose to run.

On a cool autumn evening in 1997, the primatologist Richard Wrangham was gazing into his fireplace in Cambridge, Massachusetts, turning over the...

On 19 September 1991, two German hikers, Erika and Helmut Simon, were walking near the Tisenjoch pass, 3,210 m up in Italy's Schnals Valley. In the...

In 1983 Randolph Nesse, a psychiatrist at the University of Michigan, finally got up the nerve to tell some evolutionary biologists his theory of...

In the years after the Second World War, a London double-decker bus carried two employees and, without anyone planning it, an experiment. The driver...

The children came from a rural primary school in Kenya's Rift Valley, and none had ever worn shoes. Daniel Lieberman's team filmed 16 of them running...

In 2014 and 2015, 705 Tsimane men and women aged 40 and over left their villages in the Bolivian Amazon to lie, one at a time, inside a CT scanner in...

In July 1622, in Milan, the anatomist Gaspare Aselli cut open a living, recently fed dog to show friends how the diaphragm moves.

Luciano Bernardi's team in Pavia and Florence was studying how reading and mental arithmetic, done silently or aloud, stir the heart's rhythms.

In September 1981, near Dongara in Western Australia, two insect scientists watched jewel beetles (Julodimorpha bakewelli) cruising 1-2 m above the...

Khun Chang Khian is a rural Hmong village in northern Thailand, about an hour from Chiang Mai. Mae La is a camp for refugees from Myanmar, on the...

In 1963 a National Institutes of Health (NIH) survey of arthritis among the Pima of the Gila River Indian Community, in southern Arizona, found...

In the late 1980s the pharmacologist David Bailey and his team in London, Ontario, set out to learn whether alcohol strengthens the effects of...

In December 2006, researchers at the University of California, Berkeley, described an experiment that sounds like a party game.

In 1985 the linguist Charles Hockett published a lecture titled simply F, crediting a hint from Carleton Coon. It was about f and v, the sounds you...

In April 2002 Cynthia Lucero ran the Boston Marathon. She was 28, from Guayaquil, Ecuador, had finished her doctoral dissertation days earlier and...

After the Second World War, a redrawn border divided the region of Karelia between Finland and the Soviet Union.

In 1903, workers improving the drainage at Gough's Cave in Cheddar Gorge, Somerset, uncovered a nearly complete human skeleton.

In 1974 Matthew Kluger and two colleagues reported what sounded like a contradiction: a fever in a cold-blooded animal. Their subject was the desert...

In the early 2000s, the anthropologist Michael Gurven and a Tsimane research assistant went door to door in 16 villages in lowland Bolivia.

Every night for two years in the late 1980s, the anthropologist Beverly Strassmann noted which women slept at the two menstrual huts of Sangui, a...

On 16 July 1962 a 23-year-old French geologist climbed down into a cave in the Alps, about 70 kilometers from Nice, where his team had found an...

In the late 1960s a team led by Francis A. Young tested the eyes of the Inuit residents of Barrow, Alaska. They put in drops, waited for the focusing...

On Christmas Eve 1832, bad weather pinned the Beagle near Cape Horn for six days. The summer solstice had passed, yet her young naturalist wrote that...

In 2008, archaeologists in Hohle Fels, a cave above the Ach valley in southwestern Germany, lifted a dozen pieces of hollow bone from the floor and...

A three-story wing of a suburban Pennsylvania hospital held rows of nearly identical double rooms. Each had a window low enough for a patient in bed...

In 1978 Robert Sapolsky began watching a troop of olive baboons, Forest Troop, in Kenya's Masai Mara Reserve, and kept at it for decades. The troop...

Roseto, Pennsylvania, should not have been unusual. The Italian-American town sat a short drive from Bangor and Nazareth, in country built much the...

In 2014 a group of psychologists at the University of Virginia and Harvard published 11 studies in Science whose method was almost nothing at all.

In 2008 four researchers published body measurements and DNA samples from the Ariaal of northern Kenya, a people who live by their herds.

Between 1995 and 2016, researchers at Ngogo, a chimpanzee community in Kibale National Park in western Uganda, wrote down who was born and who died.

In 1960 the anthropologist Sherwood Washburn set out a problem in Scientific American that has shaped every argument about human birth since.

For a study published in 2007, Ellen Beate Hansen Sandseter went into Norwegian preschool yards to watch children look for trouble. Not to stop them.

In January 2023, a review in Cell by Carlos López-Otín and four colleagues proposed twelve hallmarks of aging.

In December 2024, four statisticians at the National Center for Health Statistics published a short document with no argument in it. "Mortality in...

In 2017 a team of physiologists reported what they had measured at Everest Base Camp, 5,300 meters (17,400 feet) up the mountain.

In 1971 a short paper in The Lancet described the blood of Inuit on the west coast of Greenland.

In 1984 the nutrition researcher Kerin O'Dea published an experiment no drug company could have run.

Starting in 2011, thousands of older American women in the Women's Health Study wore a small accelerometer, a motion sensor that counts steps,...

Fifty-five adults spent evenings under controlled light of varying brightness while researchers measured their melatonin, the hormone that marks the...

In a university laboratory, Andrew Przybylski and Netta Weinstein sat pairs of strangers down and asked them to talk for ten minutes.

A patient arrives at a sleep clinic, not because their nights feel bad but because a wearable device has reported that their sleep was short, or...

In 2011, Betsy Sparrow, Jenny Liu and Daniel Wegner published a set of experiments in Science about what a person does with a fact when a machine is...

In 1999 the Galician city of Pontevedra began pulling cars out of its historic center. Through traffic was pushed to the edge of town, and the old...

Climbing is the easy part. This book pictures human history as a spiral staircase that turns at fire, agriculture, industry and the digital world.

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...

The proposal that depression's symptoms package the mind for sustained thought about a hard social problem.

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...

A genus of early hominins, including Lucy at 3.2 million years old, that walked upright while still climbing regularly.

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...

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...

Regions, Sardinia, Okinawa and Ikaria among them, said to hold unusual numbers of very old people.

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...

A prolonged but reversible rise in the excitability of nerve cells in the spinal cord and brain, so touch hurts and pain hurts more.

The way defaults and framing shape what people do without removing any option, as in automatic pension enrollment and presumed consent for organ...

The roughly 24-hour cycle kept by a self-winding genetic loop found in tissues throughout the body.

Yaakov Stern's account of why two people with similar Alzheimer's pathology can differ greatly in impairment.

The involuntary gasp, hyperventilation and surge in blood pressure that follow sudden skin cooling.

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.

The absence of any outward signal of human fertility. Paternity confidence, paternity confusion and alliance-building all have advocates, and no test...

Herman Pontzer's proposal that daily energy use levels off as activity rises, because active bodies spend less elsewhere.

A system in which adults besides the mother, called alloparents, invest in raising young: grandmothers, older siblings, aunts, unrelated group...

T.S. Kemp's account of how warm blood evolved: many structures changing together, keeping the animal a working whole at every step.

The main human glucocorticoid, released tens of minutes into a stress response.

Brain regions, including medial prefrontal and posterior cingulate cortex, that grow more active when no task holds the mind.

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...

Robert Dudley's proposal that the smell of ethanol in ripening fruit led ancestral primates to food, and that modern drinking misfires that...

About 150, extrapolated from a relationship between neocortex size and group size across primates.

Daniel Lieberman's term for the loop in which medicine treats the symptoms of mismatch diseases while the environments causing them are passed on.

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...

The feedback loop that grows the eyeball until its length matches its focusing power, using blur on the retina as its guide.

Making your own body heat, at five to ten times a cold-blooded animal's oxygen cost.

Dietary energy in, minus energy burned in exercise, per kilogram of fat-free mass.

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...

Abdel Omran's 1971 framework describing a shift from an age of pestilence and famine, through receding pandemics, to an age of degenerative and...

Chemical marks on DNA and its packing proteins that change how genes are read without changing the sequence.

This book's three marks, a simplified cousin of the GRADE system: ●●● strong, ●●○ probable, ●○○ emerging, small, animal-only or contested. (Prologue)

The study of why bodies are vulnerable to disease, called Darwinian medicine by Williams and Nesse in 1991.

A condition more common or severe because an organism is imperfectly adapted to a novel environment.

Aiello and Wheeler's 1995 proposal that the human brain was paid for by a shrunken gut.

Carbohydrate human enzymes cannot break down, left for colon bacteria to ferment into short-chain fatty acids.

Shinrin-yoku, named by a Japanese ministry in 1982. Its immune claims rest on very small unrandomized studies; the better-measured effects are modest...

Periods stopping because the reproductive axis has shut down under low energy availability. It can occur without visible weight loss and needs...

A gut hormone released after a meal that boosts insulin, slows stomach emptying and reduces eating.

A proposed route by which fluid enters the brain along arteries and leaves along veins, carrying waste. Whether sleep speeds that clearance or slows...

Kristen Hawkes and colleagues' proposal that older women's foraging pays for human life history, letting mothers wean earlier and conceive again...

Hunter-gatherers of Tanzania, roughly 1,200 of them, the most-studied foraging population in this book.

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...

Twelve cellular processes named in a 2023 review, from telomere attrition to chronic inflammation.

This book's name for the practical section closing most chapters, with doses, grades and cautions.

A label for one unbroken ancestral line, traced through the Y chromosome or mitochondrial DNA.

The beat-to-beat variation in the spacing of the pulse, tracking the vagus nerve's influence on the heart.

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 share of variation in a trait, within one population under one set of conditions, owed to genetic differences.

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...

David Strachan's 1989 suggestion that childhood infection carried by older siblings protects against hay fever.

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...

Raichlen, Pontzer and colleagues' proposal that human physiology expects the muscle work of squatting, kneeling and ground-sitting.

Kevin Tracey's circuit in which the brain detects inflammation and answers down the vagus nerve, telling immune cells to quiet.

A study of 10,079 adults at 52 centers worldwide, measuring sodium in 24-hour urine.

San hunter-gatherers of the Kalahari, also written !Kung, whose work diaries produced the idea of the original affluent society.

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,...

Keeping the milk-digesting enzyme switched on into adulthood. It arose at least four times through different mutations, long after people began...

Raised permeability of the gut lining, real and measurable in celiac and inflammatory bowel disease.

The randomized trial in which 640 high-risk babies ate or avoided peanut until age five.

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...

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...

Teeth that do not meet as they should: crowding, overbite, crossbite. Jaws have shortened since farming while tooth size changes only over millennia,...

Metabolic dysfunction-associated steatotic liver disease, the 2023 renaming of nonalcoholic fatty liver disease.

H.M. Frost's model in which bone remodels itself to the loads placed on it, sensed by cells called osteocytes.

The light-sensitive pigment in a third class of retinal cells, wired to the body clock rather than to vision.

A method using inherited genetic variants as natural instruments to test whether an exposure causes an outcome.

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...

Footwear with little cushioning or raised heel, and going without. A 2010 study found that habitually barefoot runners landing on the forefoot...

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...

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...

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...

A third category beside pain from damaged tissue and from damaged nerves, seen in fibromyalgia and tension-type headache.

Gordon Walls's 1942 argument that mammals passed through a nocturnal phase costing them visual equipment reptiles and birds still carry.

Sherwood Washburn's 1960 proposal that human babies are born early because a bipedal pelvis cannot pass a finished head.

Graham Rook's replacement for the hygiene hypothesis: immune regulation depends on organisms present throughout mammalian evolution, such as...

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,...

Kelly Baron's 2017 name for patients chasing the perfect sleep score a wearable reports, trusting the device more than how they feel.

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...

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...

Running or walking prey to exhaustion in the heat. Louis Liebenberg documented 10 in the central Kalahari, and historical accounts show the tactic...

The puzzle that animals with a thousand times more cells than humans do not get proportionally more cancer.

Per- and polyfluoroalkyl substances, industrial chemicals the liver cannot break down.

A score summing many gene variants of tiny individual effect. It shifts a probability rather than making a diagnosis, and works less well in...

Stephen Porges's account of a distinct vagal circuit producing a calm-and-connect state.

The signal dopamine neurons carry: a burst when a reward beats prediction, baseline when it matches, a dip when it fails to come.

Also called Tarahumara, farmers and runners of Chihuahua, Mexico. Researchers working with them named the popular romance the "fallacy of the...

Immune cells that damp down immune responses, controlled by the gene FOXP3. Their discovery won the 2025 Nobel Prize, and the Nobel Assembly called...

Slow breathing at roughly five to six breaths a minute, the pace at which breath-linked swings in heart rate grow largest.

Ellen Sandseter's six categories of the trouble children seek out: heights, speed, dangerous tools, dangerous elements, rough-and-tumble, and going...

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...

Waking time spent sitting, reclining or lying at a low energy cost. It differs from physical inactivity, meaning too little activity to meet the...

The state of a cell that is alive and busy but permanently out of the division business.

Carrying one copy of the sickle hemoglobin allele protects against severe malaria; two copies cause sickle cell disease.

The lethargy, low mood and lost appetite that travel with fever, argued in 1988 to be an organized strategy rather than debilitation.

Sitting on the floor and standing up again, scored from 10 with a point lost for each hand or knee used.

A measure of how consistent sleep timing is from night to night. Across nearly 61,000 accelerometer-wearing adults it predicted death better than...

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...

Robin Dunbar's 1998 argument that primate brains grew to manage social relationships.

The objective state of having few contacts, distinct from loneliness, the felt lack of the connection you want.

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...

Referral by a health service to choirs, walking groups, gardening or volunteering rather than to a prescription pad.

An exaggerated version of a natural signal that draws a stronger response than the real thing, such as the oversized model egg an oystercatcher...

Low-grade inflammation running for years with no infection to justify it, proposed in 2019 as a shared thread through cardiovascular disease, cancer,...

The repeated cap of DNA and protein at the end of a chromosome, shortening with each cell division.

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)...

James Neel's 1962 proposal that genes favoring efficient fat storage were selected by famine and turned harmful with plenty.

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...

A 1993 laboratory procedure: 10 minutes of dread, then a mock job talk and serial subtraction before judges.

Forager-horticulturalists of the Bolivian Amazon, with the lowest coronary artery calcium reported anywhere.

Pastoralists of northwest Kenya who get about 62% of their calories from milk.

The NOVA classification's term for industrial assemblies of substances extracted from foods, marked by ingredients never or rarely used in kitchens.

The savory taste of amino acids, named by Kikunae Ikeda in 1908 after he isolated monosodium glutamate from kombu.

The longest cranial nerve, running from the brainstem to heart, lungs, gut, liver and spleen, and the main channel of the parasympathetic nervous...

Vigorous intermittent lifestyle physical activity: short bursts of hard effort folded into ordinary life, such as stairs taken fast.

The vitamin the skin makes when ultraviolet B light strikes a cholesterol-like molecule, a process melanin slows without stopping.

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...

A people of Venezuela and Brazil whose systolic blood pressure showed no measurable rise with age, and whose sodium intake was the lowest in...

In the WalkBack trial, 701 adults recently recovered from non-specific low back pain had six sessions with a physical therapist spread over 6 months....

Any running was associated with a 27% lower risk of death from any cause, with no clear extra benefit from more. Recreational runners were no more...

No health trials exist. ●○○ The shoulder's reliance on stored elastic energy may help explain common throwing injuries, so build volume slowly.

Your body adapts to heat with repeated exposures. But in a laboratory study, 24 young, healthy adults doing light activity in humid heat could no...

the consensus of American sleep medicine. ●●○ Loud snoring, gasping or daytime sleepiness warrant a sleep assessment. See Chapters 23 and 41.

Social isolation is one of 14 modifiable risk factors; addressing all of them might prevent about 45% of dementia. ●●○ (observational) See Chapters...

In a trial of 120 older adults, walking 40 minutes three times a week for a year, after building up from 10 minutes over seven weeks, enlarged the...

Adults aged 60-90 who spent 15 or more hours a week (16.5 on average) for three months learning digital photography or quilting improved episodic...

Adults: at least 225 g (8 ounces) of seafood a week. If pregnant or breastfeeding, eat 225-340 g (8-12 ounces) of lower-mercury choices and avoid...

Strict raw-food diets are associated with underweight and lost periods. ●●○

Write a worry down, then check what happened. ●○○ It complements care rather than replacing it: persistent anxiety is treatable (Chapter 31).

Every 20-30 minutes, walk for 2-5 minutes; walking beats standing. ●●○ (consistent short trials; long-term benefit unproven)

About 30-40 minutes a day of moderate-to-vigorous activity (measured by motion sensor) weakens the link between long sitting and early death. By...

Climbing more than five flights (about 50 steps) a day was associated with 16-23% lower risk of atherosclerotic cardiovascular disease (disease of...

Sit on the floor, kneel or squat for short spells, holding a doorframe or using a low stool until your hips and ankles allow more. ●○○ With knee...

In one randomized trial, 30 minutes of supervised high-intensity resistance and impact training twice a week for 8 months raised spine bone density...

In the sitting-rising test you sit down on the floor and stand up again, starting from 5 points for each movement and losing 1 for each hand or knee...

a footstool is cheap and may help some people. Leave the phone outside: smartphone use there was associated with 46% higher odds of hemorrhoids in...

At least three days a week, practice single-leg stands, stepping, sit-to-stand or Tai Chi, plus resistance work; progress for at least 12 weeks and...

Walk in flat, flexible shoes with room for the toes, starting with about 30 minutes a day and building wear time over about 16 weeks. Or do foot...

Do not change a comfortable heel strike just because it is one. Heavier runners, and those running over 35 km (22 miles) a week, fared worse in...

Choose low heels and firm, slip-resistant soles indoors and out, not socks or slippers. Practice barefoot balance only on a clear floor beside...

Use the step and weekly-minute targets in Chapter 40; the Tsimane pattern is hours of mostly light and moderate activity.

Steady endurance training and intervals both raise VO2 max, by about 5 mL/kg/min in trials of healthy adults aged 18 to 45, intervals slightly more....

Build meals on fruit and vegetables, as DASH did, though that diet changed more than potassium. WHO suggests at least 3,510 mg of potassium a day...

Potassium-enriched salt (about 25% potassium chloride) lowers systolic pressure by about 4-5 mmHg, and more where kitchens do the salting. Do not use...

WHO's limit.

Some 44% of people with hypertension do not know it. Get checked, measure at home if your clinician advises, and never stop blood-pressure medicine...

Training raises it; chasing a nightly score is a trap (Chapter 43).

No lymph dose has been tested, but a foot free to move swelled half as much as a still one over eight hours of sitting. Follow the Chapter 6 advice...

A slow 15-minute walk widened the thoracic duct in a small study, and working leg muscles clear lymph three to six times faster than resting ones.

Walk the aisle, flex your calves, take an aisle seat; the official advice rests on indirect evidence. With a past clot or other risk factors (recent...

It did not significantly widen the thoracic duct in the same 2025 study; Chapter 10 covers breathing.

Slowly progressive weight training, begun under supervision, did not worsen breast-cancer-related lymphedema in one trial. In another, it did not...

Breathe through it at rest, walking and asleep. Mouth breathing in hard exercise is normal, and nose-only breathing lowers peak output. If your nose...

About five or six breaths a minute (say, four seconds in and six out) for 5-10 minutes, on most days; the blood-pressure trials ran for at least four...

Inhale slowly through the nose, top up with a second short inhale, then exhale slowly and fully through the mouth, for up to five minutes.

Get a sleep assessment before trying mouth tape. Never tape a blocked nose, and skip tape when you feel sick: sleep specialists worry about vomiting...

Never practice them in or near water, in the bath or while driving. Skip them if you are pregnant or have heart disease or a seizure disorder, and...

Keep hyper-palatable snacks out of sight and reach, and make whole foods the easy option at home and at work. Moving food farther away reduced how...

Start with the meals you eat most often. On a metabolic ward, people ate about 500 kcal a day less on minimally processed menus than on...

Eating home-cooked main meals more than five times a week, versus fewer than three, was associated with 28% lower odds of overweight in 11,396 UK...

Smaller portions, packages and plates reduce intake, modeled at 144-228 kcal a day if sustained across the whole diet. Eating more slowly lowers...

Sweetened drinks are among the ultra-processed foods most consistently linked to harm, and with alcohol, less is better and none is fine. ●●○ If you...

Aim for at least 25 g a day. In meta-analyses the benefit was greatest at 25-29 g, and more may help. The US adult average is about 17 g. In the...

Trial participants worked up over four weeks to about six servings a day; start with one. Yogurt, kefir, most cheeses, miso and unheated fermented...

unless a clinician recommends one for a specific reason.

Healthy microbiomes mostly, though not entirely, recover: a reason to avoid unnecessary courses, never to refuse a needed one (Chapter 20).

Garden, grow food, let children dig, and wash hands before eating.

An overnight fast lets the migrating motor complex run. But in a 12-month trial of 139 adults, eating only between 8 a.m. and 4 p.m. added no...

The omega-3 index is the share of omega-3 fats in red blood cell membranes. In national data from 2021-2023, over half of Americans aged six and over...

Make minimally processed food the easy default (Chapter 11); across 25 populations, more ultra-processed food went with more body fat.

from legumes, whole grains, vegetables and fruit, building up slowly. Benefits peaked at 25-29 g in meta-analyses, and more may help.

at least 0.8 g per kg of body weight a day, with 1.2-1.6 g/kg proposed during active weight loss, and not 2 g/kg or more for long periods. With...

Aim for 150-300 minutes a week of moderate activity plus resistance training on two or three non-consecutive days. A session can improve insulin...

If you habitually sleep under 6.5 hours, try to extend it. In 80 such adults with overweight, one sleep-hygiene session added about 1.2 hours a night...

With prediabetes, a program aiming at 7% weight loss and 150 minutes of weekly activity cut diabetes incidence by 58% over about three years. With...

chosen with a clinician and planned as long-term treatment, since weight usually returns after stopping. The trials enrolled adults with a BMI of 30...

In an eight-week trial in 40 teenage boys with fatty liver, the whole household ate meals that held free sugars (added sugars and juice) under 3% of...

Cirrhosis risk climbs steeply with heavy daily drinking, and in women it rises even at one drink a day. With significant liver scarring, graded F2...

the dose that lowered liver fat in trials.

A 3-5% loss improves liver fat, but inflammation and scarring generally need more; aim for 10%. Very-low-calorie diets need medical supervision if...

if you have type 2 diabetes, prediabetes or two or more metabolic risk factors: a FIB-4 (fibrosis-4) score from routine blood tests every one to two...

Cabbage-family vegetables measurably sped up a liver enzyme in a 36-person feeding trial; eat them as food, not as a cleanse. Supplements can injure...

Acetaminophen (paracetamol) caused 42% of 662 cases of acute liver failure at 22 US hospitals. In 38% of the unintentional overdoses, people had...

Look up your utility's PFAS results or test a private well. Where PFAS are present, under-sink reverse-osmosis and two-stage filters removed nearly...

Heating released the most particles in lab tests.

One 12-ounce cola exceeds the WHO's stricter target, under 5% of energy or roughly 25 g of free sugars a day. Diet drinks can be a bridge off sugary...

In small studies, preferred saltiness fell after two to three months of a 30-50% reduction. On blood-pressure or kidney medication, change salt...

In a trial of 33 adults, three months of eating much less sugar made puddings taste about 40% sweeter than they did to controls, but no more...

US adults in households that cook dinner most nights eat less sugar than those that rarely cook (119 vs 135 g a day), an association only.

Sniff four distinct odors from jars, about 10 seconds each, twice daily, for at least 12 weeks; start early and use strong odors. Never put oils in...

Do not smoke. Avoid intranasal zinc products; the US Food and Drug Administration warned against three in 2009 (●●●). Keep working smoke and gas...

Past infancy, offer age-appropriate whole foods that need chewing, not purees alone. Only animal studies and one-time snapshots of people support...

In a pooled analysis of 41 studies with 27,023 participants, ever-breastfed children had about a third the odds of malocclusion. Such comparisons...

Pediatric guidelines call for screening all children for snoring, and a sleep study for those with other signs of apnea. Removing enlarged tonsils...

Loud snoring, observed pauses or gasping, and daytime sleepiness warrant a doctor's visit and possibly a sleep study. In one 1990s study of employed...

A 10% weight loss predicted a 26% fall in the apnea index; drug treatment belongs with a prescriber.

Use 1,000-1,500 ppm (parts per million) fluoride toothpaste twice a day, with your dentist's guidance on amounts for young children. Keep free sugars...

No preventive benefit has been shown. The orthodontists' own white paper advises widening the palate only when there is a real underlying skeletal...

Coffee, tea, milk and water-rich foods such as fruit and vegetables all count; healthy adults in mild conditions need no glass count (Chapter 40).

The swap may modestly help weight; trials of simply drinking more are mixed.

Weigh yourself before and after long sessions. Losing more than about 2% suggests drinking more next time; any gain means you drank too much. For...

Headache, vomiting, confusion or seizures after heavy drinking during a long event, especially with weight gain, need urgent care, not more fluid.

Thirst fades with age, and urine color is an unreliable guide.

After a first calcium kidney stone, drinking more cut recurrences over 5 years from 27 in 100 people to 12 in 99. A year-long trial enrolled...

a mixture of clean water, salt and sugar. Severe dehydration needs medical care, sometimes with intravenous fluids.

Under the 2017 US guidance, babies with severe eczema, egg allergy or both start peanut-containing food "as early as 4 to 6 months of age," after a...

A dog or farm animals in the first year are linked to less asthma at school age. A small Finnish pilot, not randomized, laid forest floor in daycare...

About 30% of US outpatient antibiotic prescriptions are likely inappropriate. Never refuse or stop a prescribed antibiotic without a clinician's...

Handwashing prevents diarrheal illness. In 2016 the US Food and Drug Administration barred triclosan and 18 other antibacterial ingredients from...

In the study that linked farm milk to less asthma, boiled farm milk showed no such link. Raw milk can carry Listeria, E. coli and other germs most...

When the UV index is 3 or above, a few minutes outdoors on most days keeps most people's vitamin D adequate; when it falls below 3, as in a southern...

When the UV index is 3 or above, Cancer Council Australia advises SPF 50 or 50+, broad-spectrum and water resistant, as "the last line of defence."...

First use before 35 is associated with 87% higher melanoma risk.

Britain's National Health Service (NHS) suggests 10 micrograms (400 IU) a day in autumn and winter, all year with dark skin or little time outdoors,...

The Endocrine Society found no trial evidence for routine screening, even for people with dark skin, and suggests against it. Ask about a test if you...

Plain soap is enough. With eczema, seal each bath with moisturizer straight away: in a small trial in children, twice-daily baths sealed this way...

Use paracetamol (acetaminophen) or ibuprofen when fever makes you or your child miserable, not to hit a number. For children, give one drug at a...

Rest and fluids are standard self-care, and staying home protects others. No trial shows that rest shortens a fever.

Get prompt medical help for a baby under 3 months with 38°C (100.4°F) or more, or 3 to 6 months with 39°C (102.2°F) or more. Do the same for a fit, a...

They blunt the antibody response. Treat a distressed child afterwards as for any fever.

Do not ask for them for colds or flu, and never take leftover or borrowed pills. Experts are rethinking the rule to always finish the course, so ask...

Follow your national schedule for children and adults; if you are pregnant or have a weakened immune system, ask about live vaccines.

Stay as active as pain allows. Bed rest slowed recovery, and most acute back pain settles within weeks, with or without paracetamol (acetaminophen)....

Without warning signs, imaging does not improve outcomes, and "abnormal" findings are common in pain-free people of every age.

Choose exercise you will keep doing. In people recently recovered from back pain, a walking and education program that built up over three months to...

Learning how pain works does little for pain on its own. Structured treatment does more: eight weekly two-hour group sessions of CBT or mindfulness,...

One sleepless night lowered pain thresholds in 25 healthy adults, and in people with both insomnia and chronic pain, CBT for insomnia improves sleep...

Laughing with friends released opioids in the brains of 12 men, and holding a husband's hand damped the brain's threat response in 16 women (Chapter...

The World Health Organization advises against opioids as routine care for chronic primary low back pain. Never stop or rapidly cut prescribed opioids...

Smoking causes about one US cancer in five and more than a quarter of cancer deaths. Ask about yearly low-dose CT screening if you are 50 to 80 with...

"It is best not to drink alcohol," says the American Cancer Society. For those who do: "no more than 1 drink per day for women or 2 drinks per day...

Stay in a healthy range and avoid gaining through adult life. Skip crash diets, get clinical support if you have an eating disorder, and treat...

Aim for 150 to 300 minutes of moderate activity a week, or 75 to 150 of vigorous. The most active adults had lower risk of 13 cancers. In 889 colon...

Each 12 months of breastfeeding, over a lifetime, lowers the relative risk of breast cancer by about 4.3%. That is modest for any one woman, and...

Swedish girls vaccinated against HPV (human papillomavirus) before 17 had 88% less invasive cervical cancer.

In the US, colorectal screening starts at 45 and mammography every two years from 40 to 74; elsewhere, follow your national program. Screening also...

Rectal bleeding, iron deficiency anemia or abdominal pain deserve a doctor's visit. Three in four colorectal cancers under 50 are found late.

Don't count on melatonin; in one test of 31 supplements, contents ranged from 83% below to 478% above the label.

Weigh contraception and menopausal hormone therapy with a clinician; never stop a prescribed medicine without advice.

Daylight in the first hours after waking, and at least 250 melanopic lux at the eye through the day (light weighted for its effect on melanopsin)....

Below about 10 melanopic lux in the evening and 1 in the bedroom. Sensitivity varies fiftyfold, so judge by your own sleep. If you get up at night,...

Regularity predicted mortality better than duration in 60,977 people. Adults should aim for seven hours or more. A weekend outdoors pulls a late...

A device out of the bed and a cut-off time have better support than filters or blue-blocking glasses. Lower screen brightness does cut melatonin...

The American College of Physicians recommends cognitive behavioral therapy as the first treatment for chronic insomnia. Melatonin is not recommended...

Two hours was Taiwan's school target and is widely endorsed. China's plan specifies one to two, and the US National Academies at least one. Shade and...

Cohn's 15 minutes outdoors per hour of near work has never been tested on its own. The screen association cannot be separated from the room.

Vision screening at least once between ages 3 and 5, an eye examination before first grade, and sooner if a child squints at distance.

The US Food and Drug Administration authorized the first myopia-control spectacle lenses in September 2025, for children 6 to 12, citing 71% less...

A burst of new floaters, flashes of light, or a dark curtain across your vision means a same-day visit to an eye doctor or emergency room.

Sit toward the cool end of comfort in winter, around 18°C to 19°C (64°F to 66°F), and add a layer rather than a degree. The supporting trials are...

All three durations cut self-reported sickness absence equally in the one large trial. In open water, habituate and never swim alone (●○○). Enter...

Practice in the Finnish cohort was about 79°C for about 14 minutes, four to seven times a week. Safety: no alcohol, involved in half of Finnish sauna...

Near-daily tub bathing tracked with lower cardiovascular risk in 30,076 Japanese adults, and a 40°C to 42.5°C bath one to two hours before bed...

Eight hours at 85 dBA, four at 88, one at 94, about 15 minutes at 100. If you have to raise your voice to be heard at arm's length, treat the time as...

About 60% of maximum volume, about an hour at a time, then a break. No published research shows that following it prevents damage.

Hearing loss is common and undertreated. Aids are reasonable, low-risk preventive practice, but the cognitive benefit in ACHIEVE was confined to a...

If you use one, put it as far from the infant's head as the room allows, at the lowest volume and for the shortest time that works. Close-range...

Sing, drum, dance in time with somebody. The proposed mechanism is synchrony plus exertion, and the practice costs nothing. A social good rather than...

A stretch without engines, notifications or a screen playing to itself, ideally where you can hear weather and birds. The neurogenesis evidence is...

Parks, woodland, riversides and beaches all counted in the English survey behind the figure, whose design cannot prove direction. Canada's PaRx...

Leave the phone in your pocket, as the cortisol protocol did.

Sixteen randomized trials pooled to better depressive mood and anxiety, with standardized effect sizes of -0.64 and -0.94, in sessions of 20 to 90...

Across 92 studies, mostly at moderate to high risk of bias, prescriptions were followed by systolic (upper) blood pressure about 4.8 mmHg lower and...

A 40-second view of a flowering green roof left 150 students making fewer errors than a view of bare concrete. Surgical patients given live plants...

The one recommendation backed by natural experiments and a citywide randomized trial, and the only one that helps people who never read the advice...

Twenty trials put systolic pressure 3.15 mmHg lower in forest settings, mostly on the same day.

Across 97 reviews covering 1,039 trials and 128,119 people, physical activity produced medium reductions in depression, anxiety and distress, larger...

Bring a trusted person to the stressful thing, not just to the debrief.

One short night raised the next evening's cortisol by up to 45%. Chapters 23 and 41 own sleep.

Low control explained much of the Whitehall gradient, and long weeks track stroke risk. Fixed hours and a say in how work gets done are stress...

A green space settles the alarm on its own timetable, not instantly (Chapter 27 owns the evidence and the dose).

Meditation programs beat inactive controls modestly and no active treatment reliably. In one trial of 276 adults with anxiety disorders, an...

About five to six breaths a minute for 5 to 10 minutes. Pooled across 12 trials, breathwork produced small reductions in stress and anxiety (Chapter...

The evidence that people spend more time alone is stronger than the evidence that they feel lonelier, and time is the variable you can move. Count a...

Longitudinal and observational evidence converges on the quality of a few close relationships, not the size of a network. In practice that means...

In the only randomized trial cited here, 30 minutes of reciprocal warm touch, three days a week for four weeks, raised oxytocin and lowered blood...

Meals, the first and last hour of the day, and the bedroom overnight. The support is indirect but it is randomized: four weeks off Facebook raised...

Every push alert is one more unpredictable payout on the schedule Schüll described in casinos. Switching them off is a plausible extension of that...

A walk, a commute or a wait, taken without the device. The evidence supports this much: the default network runs during unstructured time and handles...

The addiction physician Anna Lembke recommends 30 days of abstinence from a compulsively used substance or behavior to let the reward baseline...

Across 522 randomized trials and 116,477 participants, all 21 antidepressants studied beat placebo for acute major depression, with a...

In a 2024 network meta-analysis, walking or jogging, yoga and strength training each produced moderate drops in depressive symptoms against active...

Disrupted sleep and reduced sunlight sit on the list of modern changes tracking rising depression, though the evidence is observational and tangled....

Weaker social capital appears on the same list. Chapters 29 and 42 hold the evidence on connection and health, and what to do about it.

Registry data link medication to lower two-year mortality and to fewer criminal convictions. The evidence that specific changes to a child's day...

Fertility declines with age in both sexes and more steeply for women after the mid-30s. Anyone thinking about children benefits from knowing that...

Periods that become irregular or stop during heavy training or dieting signal that intake is not covering output. The disruption can occur without...

Excess body fat disturbs the same hormonal loops from the other direction, through aromatase activity and insulin signaling. It affects ovulation in...

Both feed the stress-hormone activation that accompanies the brain's shutdown of the reproductive axis, and both have chapters of their own (Chapters...

Chemical exposure is a live suspect in the sperm-count and testosterone trends and has not been shown to cause either. Reducing unnecessary contact...

Infant on the back, on a firm, flat, non-inclined surface of their own. Keep it in the parents' room, with no soft bedding, pillows, bumpers or loose...

Look for a doula, midwife or trained companion who stays throughout, rather than staff rotating in and out. Continuous support is associated with...

Human milk oligosaccharides are a real and specific provisioning system for the infant gut. Breastfeeding is worth practical support: lactation help...

Hands in the weeks after birth, not just on the day: meals, nights, laundry, an adult to talk to. The direct evidence here is extrapolation rather...

No verified study supports a specific number of minutes, so treat anyone who gives you one with suspicion. The target is the kind, not the dose: play...

Heights, speed, real tools, rough-and-tumble, the trip out of sight. The evidence is genuinely thin, and it points toward benefit rather than harm:...

The Finnish pattern of 15 minutes per 45 minutes of teaching is a national practice, not a trial, and cannot carry a causal claim on its own. The...

Supported by ethnography rather than by trials. Low-cost, low-risk, and worth arranging if your neighborhood or school makes it possible.

Outdoor daylight during the school years protects against myopia (nearsightedness), and childhood green space is associated with better later mental...

A school-day restriction reliably reduces phone and social media time at school. The best current test found no measurable improvement in wellbeing,...

Strength predicted lower all-cause and cancer mortality in 8,762 men independently of aerobic fitness, and grip strength stratifies risk across a...

A hand dynamometer or a rise from the floor (Chapter 6) gives you a number tied to outcomes in cohort studies and to the clinical screening criteria...

Two years of attempted 25% restriction, achieved at about 12%, slowed one methylation clock by 2 to 3% and moved two others not at all. That is a...

The only published senolytic experiment in humans that measured senescent cells enrolled nine people for three days and measured no health outcome....

They will not tell you what to do, and whatever they might prompt is already in the handrail chapters.

If milk reliably brings bloating, gas or cramping, the likely explanation is lactase non-persistence, the default state for most of the world's...

Facial flushing, racing heart or nausea after a drink, most common in people of East Asian descent, signals reduced ALDH2 activity and, with...

How much vitamin D your skin makes from a given dose of sun depends on its pigment and on your distance from the equator. Chapter 19 carries the...

The standard rules of high-altitude travel apply to everyone: ascend gradually, allow rest days, learn the symptoms of acute mountain sickness, and...

Benefit rises steeply from a few thousand steps a day and flattens somewhere around 7,000 to 8,000 in the best-studied groups, earlier in older...

150 to 300 minutes a week of moderate activity, or 75 to 150 vigorous, is the guideline; mortality was lowest at roughly double that. Anything counts...

Three or four short bursts a day, a minute or two each, hard enough that talking gets awkward: stairs taken fast, a hill walked hard, a heavy bag...

About 30 to 60 minutes a week across the major muscle groups is the best-supported dose for mortality and major disease, not a minimum to build past....

Progressive, heavier training twice a week is the best-evidenced bone signal (Chapter 6). With osteoporosis or a past fragility fracture, start under...

Short spells sitting on the floor, kneeling or squatting, and carrying rather than wheeling (Chapter 6). With knee osteoarthritis avoid long deep...

This single change outranks every superfood in this chapter (Chapter 11).

Build up slowly; expect some bloating at first (Chapter 12).

with its 2018 retraction and republication understood as part of the record.

Use it if it helps you eat less; expect nothing extra from the clock. Skip it if you are pregnant or have a history of disordered eating. Never begin...

More in heat and during long exercise; during endurance events, do not drink past thirst (Chapter 17).

Outdoor light runs to thousands of lux, clear of the confusing indoor band. No trial has tested the hour; it follows from how the clock responds to...

Lower overhead lights and screen brightness rather than chase a lux target, because sensitivity varies more than 50-fold between people.

Cover standby lights, use curtains that work, put the phone face down or outside the room.

Regularity beat duration as a mortality predictor in nearly 61,000 people.

No specific bedroom temperature is supported by the studies usually cited for one, and with proper bedding the room can run cold without costing you...

Thirty seconds did as well as 90 in the only dose-tested trial. Open cold water is a different proposition: cold shock peaks at 10 to 15°C. With a...

That is the frequency linked to the largest risk reductions in the Finnish cohort (Chapter 25), and a hot bath most days is a reasonable substitute....

Ten to 30 minutes without a phone already moves stress hormones in a small study (●○○).

A week on nothing but sunlight and campfires shifted circadian timing about two hours earlier (Chapter 23); a single summer weekend achieved roughly...

The layered-network research implies that the effort you can put into relationships is finite. It buys the most in the inner layers: the closest...

Moderate-pressure contact is associated with lower cortisol, lower heart rate and higher vagal activity. No frequency has been established, so no...

In a controlled experiment, synchronized movement raised pain threshold and in-group bonding independently of exertion. Dance, a choir, a rowing...

The mortality association is with regular organizational volunteering, studied in adults 55 and over. The evidence describes a recurring commitment:...

Among 6,985 older Americans, the lowest-purpose group had more than twice the mortality of the highest over four years. The practical form is...

Do it especially for the conversations that matter, where the measured effect was clearest. The experiment tested a phone present against a phone...

In England, a general practice can refer you to a link worker alongside, or instead of, a prescription. The program is large and the outcome evidence...

Lembke's protocol is clinical reasoning, not a trial result. It is framed for ordinary overuse. It is not a treatment for substance dependence, which...

One rearrangement that requires no decision later beats one reminder that requires a decision daily. Remove the food from the house rather than...

Bring the data to a clinician and let it open a discussion about what you are experiencing. Do not diagnose yourself from a graph, and never adjust...

If a diet or regimen is costing you more in cognitive energy, money or social life than the health benefit it targets, that is the marker the...

Two weeks to see whether late coffee is costing you sleep is a measurement. Permanent monitoring with no question attached is a habit of attention,...

A gym spotter lets you do the lift and steps in only when you stall. To learn or retain something, choose or set up tools that withhold the finished...

Try the recall before the search. Take the familiar route without the navigation. The reasoning is that retrieval and spatial memory respond to use....

If writing or analysis is a skill you mean to keep, draft badly by yourself first, then use the assistant to improve what exists. This rests on a...

A shake or bar can be nutritionally complete and still lack the physical structure the gut ecosystem works on. This is about kinds of food, not any...

The phone in another room during work, the assistant off for the first draft, one route a week walked without a map. A rule set at a calm moment...

Pontevedra's escalating low-speed zones and Barcelona's superblocks are the working models. Details decide the outcome: which streets, enforced how,...

Finland's 15 minutes per 45 and Taiwan's 120 minutes a day are the two documented patterns worth citing at a school board meeting. Outdoors matters...

Chapter 42 covers what link workers do and what the evidence does and does not show. A referral to a choir or a walking group sits alongside medical...

A building sauna, a municipal pool, a public bath: the Finnish pattern treats heat exposure as housing stock rather than a luxury purchase. Chapter...

The first edition said it was. The Tsimane of Bolivia, forager-horticulturalists with no office chairs, report more pain than several comparison...

In Swedish national registries, starting medication was associated with lower death rates over two years.

and the link between night shifts and breast cancer rests on more than the single study the first edition used.

In humans, the evidence for inheriting a grandparent's experiences through epigenetic marks is weak.

There is no validated way to measure autophagy in a living person.

Gut serotonin does not cross into the brain.

The first edition blamed them for inflaming the body and making the gut lining leak. The fats people eat did change, enormously; that seed oils make...

The study cited compared garden crops in 1950 and 1999.

People at South African sites lived through it.

The systems are linked, and inflammation is one interacting cause among several, not a single root.

That pathway is a proposal with observational support.

The evidence is narrower: touch of the right kind is followed by lower cortisol and heart rate.

Early small trials were promising; larger placebo-controlled trials in Crohn's disease found no benefit.

The pain system can stay turned up a long while, but the change is reversible.

Many people lived on with lasting damage, cared for by others.

The first edition told readers to keep the bedroom at 18 to 19°C (64 to 66°F). Neither paper it cited contains that number.

Anna Lembke recommends 30 days away from a compulsive behavior, not 24 to 72 hours.

The trial the first edition cited cut days absent from work by 29%, not days of illness, which did not change.

Not "more than 600 times": most of the body's cells are red blood cells with no DNA. Dozens of round trips.

About 1 to 2% outside Africa, not 1 to 4%.

Permanent settlement is conventionally dated to about 3,600 years ago, with seasonal use far earlier, not "roughly 25,000 years".

Shared descent over about 15 million years, not 90 million.

27.5 in 2023, not 30.4.

Not only humans, orcas and pilot whales: five toothed whales, and wild chimpanzees at Ngogo in Uganda.

No single "10%" figure exists in the study cited.

After six weeks of daily mild cold, the extra heat it produced rose by roughly 180 calories a day, not 200 to 400.

In the national survey cited, 82.1% of Black Americans and 30.0% of white Americans were deficient.

The "700,000 to 2.1 million" figure had no source; about 350,000 are registered for commerce.

Brain cells do not shrink by 60%; in mice, the space between them grows by about 60%, and even that model is disputed.

The estimate depends heavily on the analysis used to make it.

About 806,000 Americans from 1999 to 2023, not "over 500,000".

Adults who survive childhood often live into their late sixties and seventies, a decade or so short of industrialized populations, and far fewer...

The first edition said generalized anxiety disorder affects about 6% of the world. The World Health Organization puts anxiety disorders of every kind...

Twelve since 2023, not nine.

The famous "9 to 17 extra years" of telomere aging compared the most and least stressed mothers in one small study, not caregiving mothers with...

About half of Americans eat less than the average requirement, which is not the same as clinical deficiency, and standard water treatment generally...

It does not "paradoxically impair cellular hydration": it dilutes the blood and makes cells swell.

The first edition said it raises oxygen uptake by 10 to 15%. The one small study behind the figure found skin oxygen readings about 10% higher in six...

Americans average about 5,100 steps a day by step counter, not "fewer than 4,000". No study supports the first edition's forecast that self-driving...

Lactase persistence took thousands of years to spread, not "about 300 generations", and its timing tracked famine and disease rather than milk...

US tweens averaged 5 hours 33 minutes and teens 8 hours 39 minutes of entertainment screen media a day in 2021.

The first edition's "50 to 150%" figure was tied to no dataset anyone could check.

The figures were attributed to the wrong studies.

The similarity tracks living together and closeness, not shared meals.

Published in 2015, with the tablet's light peaking at 452 nm.

One short night cut natural killer cell activity by about a quarter, not 70%, and a normal night restored it.

The "four to seven hours a day" figure could not be traced to a primary study, and neither could the claim that outdoor play fell by half between...

Visits of 20 to 30 minutes gave the biggest cortisol drop per minute spent, not the biggest drop overall.

The "96 times a day" figure comes from a three-day survey run for a device-insurance company, not from measurement.

Heart-rate variability appears never to have been measured in them, so the ancestral level is unknown.

No primary source exists for the first edition's comparison of hunter-gatherer and modern body-fat percentages.

The first edition tied its drowning to the Storegga Slide tsunami; a 2024 model suggests much of it was lost earlier.

No trace could be found of the 2005 paper the first edition credited with a rise in aerobic capacity in six to eight weeks.

Daniel Lieberman popularized the idea. S. Boyd Eaton and Melvin Konner proposed it in 1985 and, with Marjorie Shostak, called it a "mismatch" in 1988.

attributed to Lieberman cannot be found in his work and has been dropped.

David Carrier proposed it; Louis Liebenberg documented the hunts.

was presented as fact. A hominin roughly seven million years old, found in Chad far west of the Rift Valley, undermined it.

Four-legged animals do have the ligament the first edition said "barely exists" in them: in dogs, injuring it is among the most common orthopedic...

The first edition credited Holly Dunsworth's team with the pelvis-versus-brain explanation of early birth; their paper argues close to the opposite,...

does not absorb more ultraviolet light; it lets more through.

is the food scientist Steven Witherly's phrase, and his example was Cheetos.

compared Guahibo Amerindians, rural Malawians and US city dwellers, not the Hadza and the Yanomami.

was about bowel movements, not hip angles in chairs.

had two participants, the author James Nestor and Anders Olsson.

is folklore with no primary source.

the first edition cited was three different papers merged into one, and the minutes it recommended come from modern cohorts, not from any ancestral...

could not be traced to the World Health Organization source it was credited to.

The claim that women's stress systems react more to social threats and men's to achievement rested on one study of 50 students. Pooled across 34...