Health: quotes, facts and reflections - Page 4

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An adult fingernail grows about 3.5 millimetres a month, while a toenail grows about 1.6. That is why a fingernail takes three to six months to replace itself completely, and a toenail twelve to eighteen months.

A nail is made by the nail matrix, a layer of living tissue hidden under the skin at the base of the nail. The pale half-moon visible at the base of some nails, the lunula, is the edge of that matrix showing through. New cells made there fill with keratin, the tough protein also found in hair, and push older cells forward; the nail plate they form is dead tissue, with no nerves or blood vessels. Growth speed depends on age, season, diet and health, and it is linked to finger length: the nail on the index finger grows faster than the one on the little finger. Contrary to a popular belief, nails do not keep growing after death; the skin dries and shrinks back, which only makes them look longer.

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Heart-rate variability (HRV) measures how much the time between one heartbeat and the next changes, in milliseconds. It shifts with sleep, training, stress, illness, alcohol and breathing, so a single reading says little on its own.

A healthy heart does not beat like a metronome. The gaps between beats lengthen and shorten all the time, even with each breath: the heart speeds up slightly as you breathe in and slows as you breathe out. These changes are steered by the autonomic nervous system, which runs the body without conscious effort. When its 'rest and digest' branch, the parasympathetic system, is in charge, HRV tends to rise; when the 'fight or flight' branch takes over, it tends to fall. Higher HRV is often linked with good recovery, but it also varies with age, genes and fitness, and it naturally falls as people get older. That is why a trend measured the same way, at the same time of day, tells you more than comparing numbers with someone else.

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In a 2019 study of nearly 20,000 people in England, those who had spent at least 120 minutes in nature in the previous week were more likely to report good health and high wellbeing. The benefit peaked at around 200 to 300 minutes, and it made no difference whether the time came in one visit or several.

The study, led by Mathew White at the University of Exeter and published in Scientific Reports, used a national survey of how people in England spend time outdoors. It shows a link, not proof that nature causes better health, but other research points the same way. In 1984 the researcher Roger Ulrich found that patients recovering from gallbladder surgery in a Pennsylvania hospital went home sooner and needed fewer strong painkillers when their window looked out on trees rather than a brick wall. Suggested explanations include more exercise, cleaner and quieter surroundings, and attention restoration theory, proposed by the psychologists Rachel and Stephen Kaplan: natural scenes hold our attention gently, which gives the mind a rest from constant concentration.

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About 90% of the body's serotonin, a chemical messenger, is made in the gut, where it helps move food along. Serotonin cannot pass from the blood into the brain, so the brain makes its own supply separately.

Serotonin was named in 1948 by researchers at the Cleveland Clinic, who found a substance in blood serum that tightened blood vessels: sero- for serum, -tonin for tone. An Italian scientist, Vittorio Erspamer, had already found it in the gut in the 1930s and called it enteramine; in 1952 the two proved to be the same molecule. In the gut, lining cells called enterochromaffin cells release it when food arrives, making the intestine contract. Platelets, the blood cells involved in clotting, soak up much of the rest. The brain's serotonin, only about 1 to 2% of the total, is made by small clusters of nerve cells in the brainstem called the raphe nuclei. A protective filter, the blood–brain barrier, keeps gut serotonin out, so the gut's large share does not mean it directly controls mood.

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A Finnish study that followed 2,315 middle-aged men for about 20 years found that those who took a sauna four to seven times a week were less likely to die of heart disease, or of any cause, than those who went once a week. It shows a link, not proof that the sauna did it.

The men, aged 42 to 60, joined a long-running heart study in Kuopio, eastern Finland, in the 1980s, and researchers at the University of Eastern Finland published the sauna results in 2015. After allowing for known risk factors such as smoking, blood pressure and cholesterol, men who used the sauna four to seven times a week had a 63% lower risk of sudden cardiac death than once-a-week users. Sessions longer than 19 minutes were also linked to fewer deaths from heart disease. This is an observational study: it records what people already do rather than assigning them a routine, so men who were healthier to begin with may simply have used the sauna more. It also included only men. The sauna is part of everyday life in Finland, and Finnish sauna culture was added to UNESCO's list of intangible cultural heritage in 2020.

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Non-sleep deep rest (NSDR) is a recent name for guided relaxation done lying down and awake, often for 10 to 30 minutes. Most versions borrow from yoga nidra (“yogic sleep”) and the body scan, in which a voice moves your attention slowly through the body.

The term was coined by the Stanford neuroscientist Andrew Huberman, who promoted it on his podcast as a plain-language label for practices such as yoga nidra, “yogic sleep”. Yoga nidra in its modern form was spread in the 1970s by the Indian teacher Satyananda Saraswati; it draws on older yoga as well as Western relaxation methods of the early 20th century. A session asks you to lie still, notice your breath and follow instructions that move attention from one part of the body to the next. Research is still small. A 2002 Danish brain-imaging study found more dopamine, a chemical linked to motivation and reward, released in part of the brain during yoga nidra, and small trials report better sleep and less anxiety. NSDR is not a single clinical method, and no study shows it can replace sleep.

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Cardiorespiratory fitness, how well your heart, lungs and muscles use oxygen during hard exercise, is one of the strongest known predictors of how long people live. It is often measured as VO2 max, the most oxygen the body can use in a minute.

VO2 max is measured on a treadmill or exercise bike while a mask analyses each breath, and is given in millilitres of oxygen per kilogram of body weight per minute. An untrained man typically scores about 35 to 40, an untrained woman 27 to 31, and elite endurance athletes can exceed 80. The British physiologist Archibald Hill described the idea in the 1920s. In 2018 Cleveland Clinic researchers reported on 122,007 patients who had done treadmill tests between 1991 and 2014. After allowing for age and other factors, the least fit quarter were about five times as likely to die during the follow-up as the fittest 2 to 3%, and simply being below average carried as much risk as smoking or diabetes. Unlike age, fitness can be raised: regular endurance and interval training increase VO2 max in most people.

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Studies of places with unusually many very old people, the so-called Blue Zones, have found recurring habits such as plant-rich diets, daily movement and close social ties, but they have not established a proven recipe for long life.

The idea began in Sardinia. In the early 2000s the researchers Michel Poulain and Gianni Pes mapped villages in the island's mountainous Nuoro province where unusually many people, especially men, reached 100, circling them on the map in blue ink. In 2005 the writer Dan Buettner popularised the name in a National Geographic cover story on Sardinia, Okinawa in Japan and Loma Linda in California; the Nicoya Peninsula in Costa Rica and the Greek island of Icaria were added later. Critics point out that habits are tangled up with genes, healthcare and migration, and that some age records are unreliable: Okinawa's family registers were largely destroyed in 1945 and rebuilt afterwards. In 2024 the researcher Saul Newman won an Ig Nobel Prize, a satirical award for research that first makes people laugh and then think, for showing that many record ages come from places with poor birth records.

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Vaccine comes from vacca, Latin for cow. In 1796 the English doctor Edward Jenner showed that material from cowpox, a mild disease caught from cows, could protect people against deadly smallpox. His Latin name for cowpox, variolae vaccinae, gave the word.

Country people had long noticed that milkmaids who caught cowpox seemed to escape smallpox. On 14 May 1796 Jenner tested the idea: he took fluid from a cowpox sore on the hand of a milkmaid, Sarah Nelmes, and scratched it into the arm of James Phipps, the eight-year-old son of his gardener. When Jenner later exposed the boy to smallpox, he did not fall ill. Jenner published his results in 1798. An older method, variolation, gave people a mild dose of smallpox itself; Lady Mary Wortley Montagu had seen it practised in the Ottoman Empire and helped bring it to Britain in 1721. In 1881 Louis Pasteur proposed using vaccine for all such protective inoculations, in Jenner's honour. Smallpox was declared eradicated in 1980.

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Grip strength, how hard you can squeeze with one hand, is a good sign of overall health. In a study of nearly 140,000 adults in 17 countries, published in 2015, every 5 kg drop in grip strength went with a 16% higher risk of death over about four years, and grip predicted that risk better than blood pressure.

The study, called PURE (Prospective Urban Rural Epidemiology), was published in The Lancet. Researchers measured grip with a Jamar dynamometer, a hand-held device with a dial, in people aged 35 to 70 in high-, middle- and low-income countries, then followed them for a median of four years. Weaker grip was linked with a higher risk of dying from heart disease and from other causes, and with more heart attacks and strokes. Grip is a quick snapshot of overall muscle strength, which tends to fall with illness, inactivity and age, so doctors use it to spot frailty and sarcopenia, the loss of muscle that comes with ageing. It is an association, not proof of cause: the authors called for trials to test whether building strength actually lowers the risk.

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Drinking a very large amount of water in a short time can dilute the sodium in your blood to a dangerous level, a condition called hyponatraemia. Healthy kidneys can clear only about 0.8 to 1 litre of water an hour, so drinking much faster than that can overwhelm them.

Sodium, the main salt in blood, keeps water balanced between the inside and the outside of cells. Normal blood levels are about 135 to 145 millimoles per litre, and anything below 135 counts as hyponatraemia. When the blood becomes too dilute, water moves into cells and they swell. Brain cells are most at risk because the skull leaves no room, so symptoms include headache, nausea, confusion and, in severe cases, seizures. The problem is rare in everyday life but well known in endurance sport. In a study of the 2002 Boston Marathon, published in 2005, 13% of the 488 runners tested at the finish had hyponatraemia, and the main risk factors were taking more than four hours to finish and putting on weight during the race, a sign of drinking more than was lost in sweat. International sports medicine guidelines now advise drinking according to thirst.

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When you lower a weight or walk downhill, your muscles work while lengthening under load. This is called an eccentric action, and muscles can produce more force this way than when they shorten. It is a valuable part of strength training, but lowering every weight extremely slowly brings no proven extra benefit.

Muscles work in three ways: concentric, when they shorten, as in lifting a weight; eccentric, when they lengthen while resisting, as in lowering it; and isometric, when they hold still. During an eccentric action the links between the muscle proteins actin and myosin are pulled apart by force rather than releasing on their own, and a spring-like protein, titin, adds tension as the fibres stretch, which helps explain the extra force. The same strain causes more of the stiffness felt a day or two after unfamiliar exercise, known as delayed onset muscle soreness, though it eases as the body adapts. Eccentric exercises are also widely used in rehabilitation after injury. On tempo, a 2015 review of eight studies in the journal Sports Medicine found similar muscle growth whether each repetition lasted half a second or eight seconds, while very slow repetitions of more than ten seconds seemed less effective.

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Smell is the only human sense whose signals reach the brain's emotion and memory areas without first passing through the thalamus, the brain's relay station. That may be one reason a single scent can bring back a place or a time so vividly.

In a 2006 study at Stockholm University, Johan Willander and Maria Larsson asked 93 older adults to recall a personal memory prompted by a word, a picture or a smell. Memories triggered by smells were older: most came from the first ten years of life, while words and pictures mostly brought back the years between 11 and 20. Smell-cued memories also gave a stronger feeling of being carried back in time. A small brain-scan study led by Rachel Herz in 2004 found more activity in the amygdala, an almond-shaped region involved in emotion, when women smelled a perfume tied to a personal memory than when they saw it. This sudden return of the past is often called the Proust phenomenon, after the novelist Marcel Proust, whose narrator is carried back to childhood by the taste and smell of a madeleine cake dipped in lime-blossom tea.

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Laughter is mostly social: in Robert Provine's studies, people laughed about 30 times more often with others than alone, and fewer than one laugh in five followed anything like a joke. Laughing together also releases the brain's own pain-easing, feel-good chemicals.

Provine, an American neuroscientist at the University of Maryland, Baltimore County, and his students noted down 1,200 laughs they overheard in everyday settings. Most followed ordinary remarks rather than jokes, and speakers laughed about 46% more than their listeners. He concluded that laughter is above all a signal of friendliness and shared mood. Brain scans later showed what happens inside. In a 2017 study at the Turku PET Centre in Finland, 12 men watched comedy clips with close friends for half an hour, and their brains released endorphins, the body's own opioids, which ease pain and bring pleasure. The Oxford psychologist Robin Dunbar, one of the authors, argues that shared laughter helps humans bond in groups too large for the one-to-one grooming that keeps ape friendships going. Laughter also starts early: babies laugh months before they say their first words.

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A person with normal colour vision can tell apart somewhere between one and ten million shades, depending on how they are counted. Yet most languages manage with a dozen or fewer basic colour words, such as red, blue or green.

Colour vision begins with three kinds of cone cells in the retina, the light-sensitive layer at the back of the eye. Each kind responds best to short, medium or long wavelengths of light, roughly blue, green and red, and the brain compares their signals to produce every shade we see. Counting those shades is hard, which is why estimates vary so widely. In 1969 the anthropologist Brent Berlin and the linguist Paul Kay compared languages and found that they have between two and about a dozen basic colour terms; English has eleven. Languages also divide the spectrum differently. Russian has separate basic words for dark blue, siniy, and light blue, goluboy. A 2007 study reported that Russian speakers told two blues apart faster when one was siniy and the other goluboy, an advantage English speakers did not show, but researchers who repeated the experiment in 2020 did not find it.

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About 70% of bone's material is a hard calcium mineral, and most of the rest is collagen, a tough, slightly flexible protein. Together they make bone hard to crush but less brittle than pure mineral, while it weighs about a quarter as much as steel of the same size. And unlike steel, bone repairs itself.

A square centimetre of compact bone, the dense outer layer, can bear a crushing load of about 1.7 tonnes before it fails. Structural steel is stronger in absolute terms, but bone does its job at a fraction of the weight. It is weaker when pulled, and weaker still when twisted. What steel cannot do is maintain itself. Cells called osteoclasts constantly dissolve small patches of old bone while osteoblasts lay down new bone, so an adult replaces about a tenth of the skeleton every year. In the 19th century the German surgeon Julius Wolff described how bone adapts to the loads it carries: the bones of a tennis player's racket arm grow stronger than those of the other arm. After a fracture, the body bridges the gap with new tissue called a callus, which slowly hardens back into bone.

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Patients recovering from surgery in rooms that looked out on trees went home slightly sooner and needed fewer strong painkillers than those facing a brick wall, a 1984 study by Roger Ulrich found.

Ulrich, a researcher in healthcare design, studied the records of 46 patients who had gallbladder surgery at a Pennsylvania hospital between 1972 and 1981. He paired them by age, sex, weight and other factors, so that the main difference within each pair was the view. Patients who saw trees stayed 7.96 days on average against 8.70, took fewer doses of strong painkillers and drew fewer negative notes from nurses. The study, published in Science, was small and looked back at records rather than assigning rooms, but it is often credited with starting evidence-based healthcare design, which tests how buildings affect patients.

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StillnessHealth

Breathing slowly can calm the body's stress response, and many techniques make each breath out a little longer than the breath in, which tends to slow the heart.

Heart rate rises slightly with each breath in and falls with each breath out, a normal pattern called respiratory sinus arrhythmia. The link runs partly through the vagus nerve, the main nerve of the parasympathetic system, the 'rest and digest' side of the nervous system that slows the heart after stress. Slowing the whole breathing cycle, often to around six breaths a minute, and lengthening the out-breath seem to strengthen that calming signal. Slow breathing from the diaphragm is used alongside other treatments for stress and anxiety; it can help, but it does not replace medical care.

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Finland, a country of about 5.6 million people, has an estimated two to three million saunas, depending on how they are counted.

Counts vary: tallies of saunas in registered homes run above 2 million, while broader counts that add summer cottages, offices and public saunas pass 3 million. Most Finnish homes have one, and many blocks of flats share a sauna that residents book in turns. For Finns the sauna is a place to wash, rest and talk. It is traditionally heated with wood, and water thrown on the hot stones makes a burst of steam called löyly. In 2020 UNESCO added sauna culture in Finland to its list of the world's intangible cultural heritage. The popular line that Finland has more saunas than cars is less a statistic than a sign of how ordinary the sauna is there.

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In 1951, doctors at Johns Hopkins Hospital in Baltimore took cancer cells from Henrietta Lacks, a Black woman being treated for cervical cancer, without her knowledge or consent. Her cells, later called HeLa, were the first human cells able to keep multiplying in a laboratory, and are still used in research worldwide.

The HeLa cell line, named from the first letters of her first and last names, was used in the 1950s to test the polio vaccine and has since supported research into cancer, HIV, the human papillomavirus that causes most cervical cancers, and gene mapping. Lacks, a mother of five, died in October 1951, aged 31. Her family learned only in 1973, when researchers asked them for blood samples, that her cells had been grown and shared with laboratories around the world. Rebecca Skloot's 2010 book The Immortal Life of Henrietta Lacks brought the story to a wide audience. In 2013 the US National Institutes of Health agreed with the family on controlled access to HeLa genome data, and in 2023 her estate settled a lawsuit with the company Thermo Fisher Scientific.

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When people sing together in a choir, their breathing falls into step with the music, and their heart rates can begin to rise and fall together too.

In a 2013 study in Frontiers in Psychology, Björn Vickhoff and colleagues at the University of Gothenburg in Sweden recorded the heartbeats of fifteen 18-year-olds as they sang together. The heart naturally speeds up a little on each in-breath and slows on each out-breath, a rhythm called respiratory sinus arrhythmia. Because a song decides when everyone breathes, the singers' heart rates began to rise and fall together. The effect was strongest for a slow chant with breaths only between phrases and clear for a hymn. When the group simply hummed one note and breathed freely, their hearts did not fall into step. It was a small study, but a 2011 study of a choir in Berlin found a similar link.

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OXO Good Grips kitchen tools, launched in 1990, were designed with thick, soft handles for people whose hands hurt or grip weakly, and proved easier for everyone to use.

Sam Farber, a housewares entrepreneur who had retired, noticed that his wife Betsey, who had arthritis in her hands, struggled to hold an ordinary metal vegetable peeler. He worked with the New York design firm Smart Design, and the first 15 OXO Good Grips tools, including a swivel peeler, were introduced at the Gourmet Products Show in San Francisco in 1990. Their handles were made of soft, non-slip synthetic rubber, wide and oval so they would not twist in a wet or weak hand. The line sold far beyond people with arthritis and became a textbook example of universal design: making everyday things usable by as many people as possible without special adaptation.

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StillnessHistory

Kimjang is the Korean late-autumn tradition in which families and neighbours make kimchi, seasoned and fermented vegetables, in large batches to last the winter.

UNESCO added kimjang to its list of the Intangible Cultural Heritage of Humanity in December 2013, recognising the shared practice rather than any single recipe. The work usually begins in November, when cabbages and radishes are harvested and the weather turns cold. Napa cabbages are split, salted overnight and rinsed, then rubbed with a paste of chilli flakes, garlic, ginger, spring onion and fish sauce or salted seafood. Families traditionally packed the kimchi into earthenware jars called onggi and buried them in the ground, where the steady cool kept it fermenting slowly through the winter. Because the job is heavy, relatives and neighbours take turns helping one another's households, and part of the kimchi is often shared with people who cannot make their own.

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The Mediterranean diet is not only olive oil and vegetables; UNESCO treats it as a culture of growing, cooking and eating together.

UNESCO first inscribed the Mediterranean diet on its Intangible Cultural Heritage list in 2010 for Greece, Italy, Morocco and Spain, and in 2013 extended the listing to Cyprus, Croatia and Portugal. What it protects are skills and customs rather than nutrients: farming and fishing calendars, markets, preserving, cooking and eating together. The health interest came earlier, from the American physiologist Ancel Keys. His Seven Countries Study, begun in 1958, compared diet and heart disease across seven countries, and its results linked the low rates of heart disease in places such as Crete to meals built on olive oil, vegetables, grains, legumes and fish, with little meat.

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