Health: quotes, facts and reflections - Page 2

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StillnessHealth

While you sleep, the brain strengthens what you learned during the day. This process, called memory consolidation, works both on facts, such as names and dates, and on skills, such as playing a piece of music. After a short or broken night, the brain holds on to new learning less well.

Memory consolidation is the slow process that turns a fresh, fragile memory into a lasting one, and much of it happens during sleep. In 1997 the German researchers Werner Plihal and Jan Born showed that different parts of the night help different kinds of memory. Twenty healthy men learned lists of word pairs and practised mirror tracing, drawing a shape while watching only its reflection. Recall of the word pairs improved most over the first half of the night, when deep, slow-wave sleep dominates, while the drawing skill improved most over the second half, when REM sleep, the stage of vivid dreams, lasts longer. Researchers think that during sleep the brain replays the day's experiences and moves new memories from temporary storage in the hippocampus, deep in the brain, into longer-lasting networks in its outer layer, the cortex.

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DriveHealth

Some benefits of exercise begin on the day you do it, according to US guidance promoted by the CDC. After a single session of moderate or vigorous activity, such as a brisk walk, blood pressure can fall, anxiety can ease, and sleep that night and some kinds of thinking can improve.

The CDC (Centers for Disease Control and Prevention) is the United States' national public health agency, founded in Atlanta in 1946. Its advice on exercise follows the Physical Activity Guidelines for Americans, whose second edition, published in 2018, drew on a review of the previous decade's research. Earlier advice had focused on preventing disease over the years; the new edition also listed benefits people can feel at once. Besides easing anxiety and lowering blood pressure, a single session helps the body respond to insulin, the hormone that moves sugar from the blood into cells. Most of these effects grow with regular activity, while others, such as fitness, strength and a lasting fall in blood pressure, take weeks or months. The guidelines recommend at least 150 minutes of moderate activity a week.

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DriveHealth

Regular physical activity protects the heart, lifts mood, eases anxiety and improves sleep, according to the World Health Organization. These benefits do not depend on losing weight: people of every shape and size gain them, even when nothing changes on the scales or in the mirror.

The World Health Organization counts any movement that uses energy as physical activity: walking, cycling, sport, active play, housework and physical work. Its 2020 guidelines advise adults to do 150 to 300 minutes of moderate activity a week, such as brisk walking, or 75 to 150 minutes of vigorous activity, such as running, plus muscle-strengthening exercise on at least two days. In 2022 about 31% of adults worldwide, some 1.8 billion people, fell short of that. Weight is a poor guide to these benefits. The US Physical Activity Guidelines state that they are generally independent of body weight, and a 2014 analysis of ten studies found that fit people who were overweight or obese had death rates similar to fit people of normal weight, while unfit people had about twice the risk, whatever their weight.

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StillnessMind

Sleeping soon after you learn something helps you remember it. In a 2012 study, people who learned word pairs in the evening and slept soon afterwards remembered more 24 hours later than people who learned them in the morning and spent the day awake first.

The study was led by Jessica Payne of the University of Notre Dame, with colleagues including Robert Stickgold of Harvard Medical School. Volunteers learned pairs of words at 9 am or 9 pm. Twelve hours later those who had slept remembered more, mainly because a day awake had worn away memory for pairs of unrelated words, which are harder to link in the mind. After 24 hours everyone had had one night's sleep and one day awake, only in a different order, and those who slept soon after learning still remembered more. Memory also faded more slowly across a day awake when a night's sleep had come first, which suggests that sleep steadies new memories against the interference of waking life. It is one reason sleep researchers advise against giving up sleep to cram for an exam.

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DriveHealth

According to US health guidance promoted by the CDC, adults who sit less and do any amount of moderate or vigorous activity gain some health benefits. Since 2018 even a few minutes count, such as climbing a few flights of stairs; earlier advice counted only sessions of 10 minutes or more.

The Physical Activity Guidelines for Americans are issued by the US Department of Health and Human Services, and the CDC, the country's national public health agency, turns them into everyday advice. The first edition, in 2008, said activity had to last at least 10 minutes at a time to count, because there was too little evidence about shorter bouts. For the 2018 edition an advisory committee reviewed the newer research and concluded that activity of any length adds to the benefits. It also found that, for the risk of dying early, the biggest gain comes when an inactive person starts doing just 60 minutes a week: in the guidelines' words, some physical activity is better than none. The full target for adults remains 150 to 300 minutes of moderate activity a week, plus muscle-strengthening on two days.

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StillnessHealth

NHS guidance links a fibre-rich diet with lower risk of heart disease, stroke, type 2 diabetes and bowel cancer, and recommends 30g of fibre a day for adults. On average, UK adults eat only about 20g.

The 30g target dates from 2015, when the UK's Scientific Advisory Committee on Nutrition reviewed the evidence on carbohydrates and health and raised the recommended amount. Four years later a large review commissioned by the World Health Organization and published in The Lancet pooled 185 long-term studies and 58 clinical trials. People who ate the most fibre had a 15 to 30% lower risk of dying from any cause or from heart disease, and of developing heart disease, stroke, type 2 diabetes and bowel cancer, than those who ate the least. The largest risk reductions were seen at 25 to 29g a day, and the trends suggested that more could help further. The NHS shows what 30g looks like: wholemeal toast with peanut butter and an orange; wholemeal spaghetti with a lentil sauce; and a baked potato in its skin with carrots and green beans.

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DriveMind

A new habit is easier to remember when it is attached to an existing cue: after coffee, after brushing teeth, after opening your laptop.

Psychologists call the familiar routine a cue. Habits form when the same action follows the same cue again and again, until the cue starts the behaviour almost by itself. From the 1990s the psychologist Peter Gollwitzer showed that people who make a specific if-then plan, such as ‘after I pour my coffee, I will stretch for two minutes’, carry out their goals more often than people who simply intend to. He called these plans implementation intentions. The Stanford researcher BJ Fogg calls the existing routine an anchor. Patience helps too. In a 2010 study at University College London, 96 volunteers repeated a new daily habit: half needed less than 66 days before it felt automatic and half needed more, with a range of 18 to 254 days.

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StillnessHealth

Sleep is part of learning, not a pause from it: while you sleep, the brain goes back over what you practised during the day and strengthens it. That is why a new skill often runs more smoothly the next morning than it did the evening before.

In a 2002 study at Harvard Medical School, led by Matthew Walker, volunteers learned to type a short number sequence as quickly and accurately as they could. After a night's sleep they were about 20 per cent faster, with no loss of accuracy, while the same number of hours awake brought no significant gain. The size of the improvement was linked to how much light sleep, known as stage 2, people had, especially late in the night. Animal studies from the 1990s suggest how this might work: in rats, groups of brain cells that were active while the animals explored became active together again during sleep, as if the day were being replayed. It is one reason why an extra tired hour at the desk may help less than a full night's sleep.

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StillnessHealth

Fibre is good for the gut and the heart, but adding a lot at once can cause bloating and wind. Increase fibre-rich foods such as wholegrains, beans, fruit and vegetables over a few weeks, and drink plenty of fluids so the fibre can do its work.

Fibre is the part of plant foods that the small intestine cannot digest. Some kinds pass through largely unchanged and hold water, which keeps stools soft; that is why fluid matters. Other kinds are broken down by bacteria in the large intestine, which releases gas, so a sudden jump in fibre can bring bloating and wind until the gut adjusts. The NHS advises increasing fibre gradually and drinking plenty of fluids. UK guidelines recommend 30 g a day for adults, yet most adults eat only about 20 g. A 2019 review in The Lancet, covering 185 long-term studies and 58 clinical trials, found that people who ate the most fibre had a 15 to 30 per cent lower risk of heart disease, stroke, type 2 diabetes, bowel cancer and early death than those who ate the least.

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StillnessMind

Cyclic sighing, breathing in twice through the nose and then out slowly and fully, lifted mood more than mindfulness meditation in a 2023 Stanford study. Of four methods that 108 adults practised for five minutes a day for a month, it gave the biggest rise in good mood and the biggest drop in resting breathing rate.

The study was led by the psychiatrist David Spiegel and the neuroscientist Andrew Huberman and published in Cell Reports Medicine. Most volunteers came from an undergraduate psychology class at Stanford, and they were assigned to groups at random. The other breathing exercises were box breathing, with equal counts for breathing in, holding, breathing out and holding again, and cyclic hyperventilation, deep breaths in and short breaths out followed by holding the breath. In cyclic sighing the second, shorter breath tops up the lungs before the long exhale. A long, slow exhale is thought to calm the body through the vagus nerve, which slows the heart. People also sigh on their own every few minutes, which helps reopen tiny air sacs in the lungs. With about a hundred mostly young, healthy volunteers and one month of practice, the study is encouraging but small.

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WonderMind

Cognitive reserve is the idea that education, mentally demanding work and a lifetime of learning may help some people keep thinking clearly despite ageing or brain disease. Two people with similar brain damage can show very different symptoms.

The idea took shape after a 1988 study led by the American neurologist Robert Katzman, which examined the brains of 137 nursing-home residents after death. Ten had plaques typical of Alzheimer's disease, yet in life they had been among the best performers on memory and thinking tests, and their brains were heavier and held more nerve cells than those of their peers. The neuropsychologist Yaakov Stern later developed the concept, arguing that education and mental activity help the brain cope with damage by using its networks more efficiently or finding other routes. The 2024 report of the Lancet Commission on dementia lists less education in early life among 14 risk factors that can be changed. Bilingualism has also been proposed as a source of reserve, but studies disagree, so speaking two languages is not a proven protection.

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DriveMind

A single session of aerobic exercise, such as a brisk run or bike ride, can raise blood levels of BDNF, a protein that helps nerve cells survive, grow and form new connections. The rise is temporary, and its size varies from person to person.

BDNF stands for brain-derived neurotrophic factor. Yves-Alain Barde and Hans Thoenen first isolated it from pig brain in 1982, and it is especially active in the hippocampus, a region central to learning and memory. In 1995 Carl Cotman's team at the University of California, Irvine found that rats given running wheels made more BDNF in the hippocampus. In people, a 2017 analysis of 55 studies found that blood BDNF was higher after a single session of exercise, with longer sessions giving bigger rises; the effect was clear in men but not in women. Blood levels are only an indirect guide to what happens inside the brain. The findings support a link between exercise and plasticity, the brain's ability to change, without proving that BDNF explains the clear-headed feeling after a walk.

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StillnessMind

Losing sleep reliably weakens alertness and attention, and it can also impair judgement, impulse control and control of emotions. People are often poor judges of how impaired they are.

Much of the evidence comes from simple tests of sustained attention, such as pressing a button whenever a light appears at random, which reveal lapses and microsleeps, moments of sleep lasting a few seconds. In a 2003 study at the University of Pennsylvania, volunteers who slept six hours a night for two weeks ended up doing as badly on such tests as people kept awake for up to two nights, yet they rated themselves only slightly sleepy. In a 2000 Australian study, 17 to 19 hours without sleep left performance on some tests as poor as at a blood alcohol level of 0.05%, the drink-driving limit in much of Europe. Emotions suffer too: after a night without sleep, the amygdala, the brain's threat detector, reacts more strongly to unpleasant pictures and is less restrained by the front of the brain.

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StillnessMind

Gratitude exercises, such as writing down a few things you are thankful for each week, raise wellbeing slightly on average. A 2025 review of studies with nearly 25,000 people in 28 countries found a real but small effect that varied between countries and methods.

One of the first experiments on the practice was a 2003 study by the psychologists Robert Emmons and Michael McCullough. Students who kept a weekly list of things they were grateful for felt better about their lives than those who listed everyday hassles, and a rise in good mood was the most consistent result. The 2025 meta-analysis, a study that pools the results of earlier studies, was published in the journal PNAS by a team that included McCullough. It combined 145 papers covering 24,804 participants and put the average effect at about 0.19 on a standard scale on which 0.2 counts as small. Effects were larger when researchers measured positive feelings, when several kinds of gratitude exercise were combined, and in studies that assigned people to groups by chance. The authors could not explain why results varied between countries and called for more research.

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WonderHealth

The epidermis, the outer layer of the skin, renews itself constantly. New cells form at its base, move up to the surface over several weeks, harden and flake away. Classic estimates put a full turnover at roughly 40 to 56 days.

The epidermis is thin, about a tenth of a millimetre over most of the body and about half a millimetre on the soles of the feet, and it has no blood vessels of its own. About 90% of its cells are keratinocytes, which fill with a tough protein called keratin as they rise. A cell takes about two weeks to climb from the base to just below the surface, then roughly four more weeks to cross the outermost layer: about 15 layers of flat, dead cells, sealed with fats, that keep water in and germs out. The pace varies with age and body site and tends to slow as we get older. In psoriasis, a skin condition, cells make the journey in a few days instead of weeks, which causes thick, scaly patches.

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WonderHealth

A red blood cell circulates for about 100 to 120 days, carrying oxygen from the lungs to the body. Worn-out cells are then removed and broken down, and the bone marrow makes about 2.4 million new ones every second to replace them.

An adult has roughly 20 to 30 trillion red blood cells. As they mature in the bone marrow, they push out their nucleus and most of their inner machinery to make room for haemoglobin, the iron-rich protein that carries oxygen. Without a nucleus a cell cannot make new proteins or repair itself, so it slowly wears out. Old cells are swallowed by large immune cells called macrophages, mainly in the spleen and liver. The iron goes back to the bone marrow to build new cells, and the rest of the haem, the iron-holding part of haemoglobin, is turned into bilirubin, a yellow pigment that the liver releases in bile. The lifespan was first measured in 1919 by the British-born American pathologist Winifred Ashby, who tracked transfused blood cells and showed they could survive for about 110 days, far longer than the two or three weeks then assumed.

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WonderHealth

The cells in your taste buds are replaced all the time: studies in rats and mice put their average life at about 8 to 12 days. Different kinds of taste cell last for different lengths of time.

Adults have roughly 2,000 to 8,000 taste buds, mostly on the small bumps of the tongue, with others on the palate and in the throat. Each bud is a cluster of about 50 to 100 cells, supplied with new cells made in the surrounding lining. The first estimate came in 1965, when Lloyd Beidler and Robert Smallman tracked labelled cells in rats and found an average life of about ten days. A 2013 study in mice showed that the types differ. Cells that detect sweet, bitter and savoury (umami) tastes were replaced fastest, half of them within about 8 days, while cells that respond to sour lasted longer, with half gone only after about 22 days. The popular “tongue map” is a myth: every part of the tongue with taste buds can sense all the basic tastes.

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StillnessHealth

A 2013 study in mice found that the brain cleared amyloid-beta, a protein that builds up in Alzheimer's disease, faster during sleep. A 2024 mouse study, which used a small fluorescent dye and different methods, found clearance was slower during sleep. Scientists are still debating how sleep affects the brain's waste removal.

The 2013 study came from Maiken Nedergaard's laboratory at the University of Rochester, which in 2012 had described what it called the glymphatic system: cerebrospinal fluid, the clear liquid around the brain, flows in along channels around blood vessels and washes through the tissue. Her team reported that the space between brain cells widened by about 60% during sleep, letting fluid flow more freely. In 2024 Nick Franks and William Wisden at Imperial College London measured the movement of dyes directly and found clearance markedly reduced in sleeping and anaesthetised mice. In 2025 Nedergaard's group reported that during non-REM sleep, the stages without the rapid eye movements of dreaming sleep, which fill most of the night, slow waves of the chemical messenger noradrenaline make blood vessels tighten and relax, pumping fluid into the brain. The methods differ, and none of these studies was in humans.

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StillnessHealth

Most healthy adults need about seven to nine hours of sleep a night, although the exact amount varies from person to person. Teenagers need more, around eight to ten hours, and for people over 65 the advice is seven to eight.

The figures come from expert panels that reviewed the research in 2015. The US National Sleep Foundation recommended seven to nine hours for adults aged 18 to 64, and the American Academy of Sleep Medicine and the Sleep Research Society advised adults to sleep at least seven hours regularly. Sleeping less than that on most nights is linked to weight gain, diabetes, high blood pressure, heart disease, depression and more accidents. A few people genuinely need less: in 2009 researchers in San Francisco found a rare variant of a gene called DEC2 in people who naturally slept about six hours a night and felt rested. Such people are rare. A practical check is how you feel during the day: whether you wake refreshed, stay alert without leaning on caffeine and can concentrate on ordinary tasks.

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StillnessHealth

Morning light does more than brighten a room: it helps reset the body's internal clock, which times alertness, hormones and sleep. The clock runs slightly longer than 24 hours, so without that daily reset it would slowly drift later.

The signal comes from a third kind of light-sensitive cell in the eye, separate from the rods and cones we see with. These cells, identified in 2002 by teams including those of David Berson and Samer Hattar, contain a pigment called melanopsin that responds most to blue light. They report to the suprachiasmatic nucleus, a tiny cluster of nerve cells in the hypothalamus, at the base of the brain, that acts as the body's master clock. A 1999 Harvard study put the human clock's natural cycle at about 24 hours and 11 minutes. Morning light shifts the clock earlier; bright light late in the evening shifts it later and delays melatonin, the hormone that signals night. The clock's molecular machinery earned Jeffrey Hall, Michael Rosbash and Michael Young the 2017 Nobel Prize in Physiology or Medicine.

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StillnessHealth

Caffeine lingers in the body for hours: healthy adults usually take three to seven hours, often about five, to clear half of what they consume. This is its half-life. Smoking shortens it, while pregnancy, the contraceptive pill and some medicines lengthen it, so the same coffee lasts longer in some people.

Caffeine keeps you alert by blocking adenosine, a chemical that builds up in the brain while you are awake and makes you feel sleepy. From a drink it is absorbed within about 45 minutes and peaks in the blood after one to two hours. The liver then breaks it down, mainly with an enzyme called CYP1A2. In smokers the half-life is 30 to 50 percent shorter; the contraceptive pill can make it considerably longer, and late in pregnancy it can reach 15 hours. In a 2013 study at Henry Ford Hospital in Detroit, 400 milligrams of caffeine, about three mugs of filter coffee, cut total sleep by more than an hour even when it was taken six hours before bed. The researchers advised avoiding large amounts of caffeine for at least six hours before going to sleep.

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DriveHealth

Exercise snacks, bursts of hard effort about a minute long repeated a few times a day, can improve heart and lung fitness. Running up a few flights of stairs is a typical example. Studies find that if the bursts leave you breathing hard, they help even people who otherwise do little exercise.

In a 2019 Canadian study, inactive young adults climbed three flights of stairs (60 steps) briskly, three times a day with one to four hours between climbs, on three days a week. After six weeks their peak oxygen uptake, the standard measure of heart and lung fitness, had risen modestly compared with a group that did nothing. In 2022, researchers used wrist trackers worn by about 25,000 volunteers in UK Biobank, a large British health study, all adults who did no formal exercise, to find short bursts of vigorous everyday activity such as very fast walking or stair climbing. People with about three such bursts a day, each lasting one or two minutes, had a 38 to 40 percent lower risk of dying over roughly seven years. This is an association rather than proof. What counts is intensity: a gentle stroll does not qualify.

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DriveHealth

In a 1990 Boston study, nine frail nursing-home residents aged around 90 nearly tripled their leg strength after eight weeks of weight training. Their strength rose by an average of 174 percent, a sign that muscle keeps responding to training even in very old age.

The study was led by Maria Fiatarone with researchers from Tufts University and published in JAMA, the journal of the American Medical Association. Ten volunteers living at the Hebrew Rehabilitation Center for Aged in Boston, the oldest aged 96, trained their thigh muscles on weight machines at high intensity; nine completed the programme. Besides the strength gain, their thigh muscles grew by about 9 percent and their speed on a heel-to-toe walking test rose by 48 percent. Age-related muscle loss, called sarcopenia, raises the risk of falls, fractures and losing independence, and inactivity speeds it up. The NHS and the World Health Organization advise adults of every age to do muscle-strengthening activity on at least two days a week.

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DriveHealth

A short walk after a meal can blunt the rise in blood sugar (glucose) that follows eating, compared with sitting still. Working muscles pull glucose out of the blood to use as fuel, and they can do this partly without the help of insulin.

Muscle cells take in glucose through protein gateways on their surface called GLUT4 transporters. Insulin normally brings these gateways to the surface, but muscle contraction can do so on its own, which is why movement lowers blood sugar even when insulin works poorly, as in type 2 diabetes. In a 2016 study at the University of Otago in New Zealand, 41 adults with type 2 diabetes tried two plans for two weeks each: walking for 30 minutes once a day, or for 10 minutes after each main meal. With the after-meal walks, the rise in blood sugar after eating was about 12 percent lower overall and 22 percent lower after the evening meal, which in this group tended to be the most carbohydrate-rich meal and was often followed by sitting. A walk is a helpful habit, not a replacement for medication, diet advice or a doctor's care.

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