The Body: A Guide for Occupants by Bill Bryson

Rating: 7/10

Bill Bryson is one of my favourite authors. While his witty travelogues are a favourite fixture on my bookshelf, it was A Short History of Nearly Everything (one of my all-time favourites) that cemented his spot near the top of my list. Now, instead of looking outwards, Bryson peers inwards in The Body.

Across 23 chapters, each focusing on a specific corporeal topic/concept, Bryson shares interesting titbits, eye-opening research, and engaging anecdotes that shine a light on the complexities of the human body.

My notes are structured across those 23 chapters, but likely don’t give a good view of the book, as I mostly saved interesting factoids.

It is important to distinguish between probability and destiny.

How to build a human

  • Altogether, according to the RSC, the full cost of building a new human being, using the obliging Benedict Cumberbatch as a template, would be a very precise $151,578.46.
  • the only thing special about the elements that make you is that they make you. That is the miracle of life.
  • you blink fourteen thousand times a day—so much that your eyes are shut for twenty-three minutes of every waking day.
  • No one can say why those 7 billion billion billion have such an urgent desire to be you. They are mindless particles, after all, without a single thought or notion between them. Yet somehow for the length of your existence, they will build and maintain all the countless systems and structures necessary to keep you humming, to make you you, to give you form and shape and let you enjoy the rare and supremely agreeable condition known as life.
  • Unpacked, you are positively enormous. Your lungs, smoothed out, would cover a tennis court, and the airways within them would stretch nearly from coast to coast. The length of all your blood vessels would take you two and a half times around Earth. The most remarkable part of all is your DNA (or deoxyribonucleic acid). You have a meter of it packed into every cell, and so many cells that if you formed all the DNA in your body into a single strand, it would stretch ten billion miles, to beyond Pluto. Think of it: there is enough of you to leave the solar system. You are in the most literal sense cosmic.
  • Yet somehow when all of these things are brought together, you have life. That is the part that eludes science. I kind of hope it always will.

The outside: skin and hair

  • We shed skin copiously, almost carelessly: some twenty-five thousand flakes a minute, over a million pieces every hour. Run a finger along a dusty shelf, and you are in large part clearing a path through fragments of your former self. Silently and remorselessly we turn to dust.
  • Curiously, we don’t have any receptors for wetness. We have only thermal sensors to guide us, which is why when you sit down on a wet spot, you can’t generally tell whether it really is wet or just cold.
  • It has been suggested that light skin may be a consequence of human migration and the rise of agriculture. The argument is that hunter-gatherers got a lot of their vitamin D from fish and game and that these inputs fell sharply when people started growing crops, especially as they moved into northern latitudes. It therefore became a great advantage to have lighter skin, to synthesize extra vitamin D.
  • In regions like northern Europe and Canada, it isn’t possible in the winter months to extract enough vitamin D from weakened sunlight to maintain health no matter how pale one’s skin, so vitamin D must be consumed as food, and hardly anyone gets enough—and not surprisingly. To meet dietary requirements from food alone, you would have to eat fifteen eggs or six pounds of swiss cheese every day, or, more plausibly if not more palatably, swallow half a tablespoon of cod liver oil. In America, milk is helpfully supplemented with vitamin D, but that still provides only a third of daily adult requirements. In consequence, some 50 percent of people globally are estimated to be vitamin D deficient for at least part of the year.
  • Lighter-colored eyes and hair evolved somewhere around the Baltic Sea about six thousand years ago. It’s not obvious why. Hair and eye color don’t affect vitamin D metabolism, or anything else physiological come to that, so there seems to be no practical benefit. The supposition is that these traits were selected for as tribal markers or because people found them more attractive. If you have blue or green eyes, it’s not because you have more of those colors in your irises than other people but because you simply have less of other colors.
  • In all mammals, when they are cold, the muscles around their hair follicles contract in a process known formally as horripilation but more commonly as getting goose bumps. In furry mammals, it adds a useful layer of insulating air between the hair and the skin, but in humans it has absolutely no physiological benefit and merely reminds us how comparatively bald we are.
  • Every hair on your body has a growth cycle, with a growing phase and a resting phase. For facial hair a cycle is normally completed in four weeks, but a scalp hair may be with you for as much as six or seven years. A hair in your armpit is likely to last about six months, a leg hair for two months.
  • Most quadrupeds cool by panting, which is incompatible with sustained running and simultaneous heavy breathing, especially for furry creatures in hot climates. Much better to do as we do and seep watery fluids onto nearly bare skin, which cools the body as it evaporates, turning us into a kind of living air conditioner. As Jablonski has written, “The loss of most of our body hair and the gain of the ability to dissipate excess body heat through eccrine sweating helped to make possible the dramatic enlargement of our most temperature-sensitive organ, the brain.”
  • In another widely reported study, the Belly Button Biodiversity Project, conducted by researchers at North Carolina State University, sixty random Americans had their belly buttons swabbed to see what was lurking there microbially. The study found 2,368 species of bacteria, 1,458 of which were unknown to science. (That is an average of 24.3 new-to-science microbes in every navel.) The number of species per person varied from 29 to 107. One volunteer harbored a microbe that had never been recorded outside Japan—where he had never been.
  • Studies of scratching showed that the most prolonged relief comes from scratching the back but the most pleasurable relief comes from scratching the ankle.

Microbial you

  • E. coli can reproduce seventy-two times in a day, which means that in three days they can rack up as many new generations as we have managed in the whole of human history. A single parent bacterium could in theory produce a mass of offspring greater than the weight of Earth in less than two days. In three days, its progeny would exceed the mass of the observable universe. Clearly that could never happen, but they are with us already in numbers beyond imagining. If you put all Earth’s microbes in one heap and all the other animal life in another, the microbe heap would be twenty-five times greater than the animal one.
  • “From the 1950s through the 1990s,” he says, “roughly three antibiotics were introduced into the U.S. every year. Today it’s roughly one new antibiotic every other year. The rate of antibiotic withdrawals—because they don’t work anymore or have become obsolete—is twice the rate of new introductions. The obvious consequence of this is that the arsenal of drugs we have to treat bacterial infections has been going down. There is no sign of it stopping.”
  • In 1945, the year that Alexander Fleming won the Nobel Prize, a typical case of pneumococcal pneumonia could be knocked out with forty thousand units of penicillin. Today, because of increased resistance, it can take more than twenty million units per day for many days to achieve the same result. On some diseases, penicillin now has no effect at all. In consequence, the death rate for infectious diseases has been climbing and is back to the level of about forty years ago.
  • At the current rate of spread, antimicrobial resistance is forecast to lead to ten million preventable deaths a year—that’s more people than die of cancer now—within thirty years,

The brain

  • For each visual input, it takes a tiny but perceptible amount of time—about two hundred milliseconds, one-fifth of a second—for the information to travel along the optic nerves and into the brain to be processed and interpreted. One-fifth of a second is not a trivial span of time when a rapid response is required—to step back from an oncoming car, say, or to avoid a blow to the head. To help us deal better with this fractional lag, the brain does a truly extraordinary thing: it continuously forecasts what the world will be like a fifth of a second from now, and that is what it gives us as the present. That means that we never see the world as it is at this very instant, but rather as it will be a fraction of a moment in the future.
  • the brain manufactures all the components that make up our senses. It is a strange, nonintuitive fact of existence that photons of light have no color, sound waves no sound, olfactory molecules no odors.
  • As James Le Fanu has put it, “While we have the overwhelming impression that the greenness of the trees and the blueness of the sky are streaming through our eyes as through an open window, yet the particles of light impacting on the retina are colourless, just as the waves of sound impacting on the eardrum are silent and scent molecules have no smell. They are all invisible, weightless, subatomic particles of matter travelling through space.” All the richness of life is created inside your head.
  • Memories are categorized in many different ways, and no two authorities seem to use quite the same terminologies. The most frequently cited divisions are long-term, short-term, and working (for duration) and procedural, conceptual, semantic, declarative, implicit, autobiographical, and sensual (for type).
  • Fundamentally, however, memories come in two principal varieties: declarative and procedural. Declarative memory is the kind you can put into words—the names of state capitals, your date of birth, how to spell “ophthalmologist,” and everything else you know as fact. Procedural memory describes the things you know and understand but couldn’t so easily put into words—how to swim, drive a car, peel an orange, identify colors.
  • The brain takes a long time to form completely. A teenager’s brain is only about 80 percent finished (which may not come as a great surprise to the parents of teenagers). Although most of the growth of the brain occurs in the first two years and is 95 percent completed by the age of ten, the synapses aren’t fully wired until a young person is in his or her mid- to late twenties.
  • the person in question will almost certainly have more impulsive, less reflective behavior than his elders and will also be more susceptible to the effects of alcohol.
  • There seems to be an almost limitless number of curious or bizarre syndromes and conditions associated with neural disorders. Anton-Babinski syndrome, for instance, is a condition in which people are blind but refuse to believe it. In Riddoch syndrome, victims cannot see objects unless they are in motion. Capgras syndrome is a condition in which sufferers become convinced that those close to them are impostors. In KlĂźver-Bucy syndrome, the victims develop an urge to eat and fornicate indiscriminately (to the understandable dismay of loved ones). Perhaps the most bizarre of all is Cotard delusion, in which the sufferer believes he is dead and cannot be convinced otherwise.

The head

  • Ekman concluded that six expressions are universal: fear, anger, surprise, pleasure, disgust, and sorrow. The most universal expression of all is a smile,
  • No society has ever been found that doesn’t respond to smiles in the same way. True smiles are brief—between two-thirds of a second and four seconds. That’s why a held smile begins to look menacing. A true smile is the one expression that we cannot fake. As the French anatomist G.-B. Duchenne de Boulogne noticed as long ago as 1862, a genuine, spontaneous smile involves the contraction of the orbicularis oculi muscle in each eye, and we have no independent control over those muscles. You can make your mouth smile, but you can’t make your eyes sparkle with feigned joy.
  • All the many species of hominids that preceded us had prominent browridges, but we Homo sapiens gave them up in favor of our small, active eyebrows. It’s not easy to say why. One theory is that eyebrows are there to keep sweat out of the eyes, but what the eyebrows do really well is convey feelings.
  • In one interesting experiment, subjects were shown two sets of digitally doctored photographs of well-known people: one with the eyebrows eliminated and the other with the eyes themselves taken away. Surprisingly, but overwhelmingly, volunteers found it harder to identify the celebrities without eyebrows than without eyes.
  • It’s curious that we always speak of our five senses because we have way more than that. We have a sense of balance, of acceleration and deceleration, of where we are in space (what is known as proprioception), of time passing, of appetite. Altogether (and depending on how you count them) we have as many as thirty-three systems within us that let us know where we are and how we are doing.
  • Tears come in three varieties: basal, reflex, and emotional. Basal are the functional ones that provide lubrication. Reflex tears are those that emerge when the eye is irritated by smoke or sliced onions or similar. And emotional tears are of course self-evident, but they are also unique. We are the only creatures that cry from feeling, as far as we can tell. Why we do so is another of life’s many mysteries.
  • Because we were once nocturnal, our ancestors gave up some color acuity—that is, sacrificed cones for rods—to gain better night vision. Much later, primates re-evolved the ability to see reds and oranges, the better to identify ripe fruit, but we still have just three kinds of color receptors compared with four for birds, fish, and reptiles. It’s a humbling fact, but virtually all nonmammalian creatures live in a visually richer world than we do.
  • You can experience this blind spot by means of a simple trick. First, close your left eye and stare straight ahead with the other. Now hold up one finger from your right hand as far from your face as you can. Slowly move the finger through your field of vision while steadfastly staring straight ahead. At some point, rather miraculously, the finger will disappear. Congratulations. You have found your blind spot.
  • As the acoustics scientist Mike Goldsmith has put it, “If we could hear quieter sounds still, we would live in a world of continuous noise, because the omnipresent random motion of air molecules would be audible. Our hearing really could not get any better.” From the quietest detectable sound to the loudest is a range of about a million million times of amplitude.
  • Inside the vestibular channels is a gel that acts a little like the bubbles in a carpenter’s level, in that the gel’s movements from side to side or up and down tell the brain in which direction we are traveling
  • That gel thickens as we age and doesn’t slosh around as well, which is one reason why the elderly are often not so steady on their feet
  • Once you disable a stereocilium, it remains lost to you forever. There isn’t any particular reason for this. Stereocilia grow back perfectly well in birds. They just don’t do it in us. The high-frequency ones are at the front and the low-frequency ones farther in. This means that all sound waves, high and low, pass over the high-frequency cilia, and this heavier traffic means they wear out more quickly.
  • When loss of balance is prolonged or severe, the brain doesn’t know quite what to make of it and interprets it as poisoning. That is why loss of balance so generally results in nausea.
  • Aroma molecules typically activate not one type of odor receptor but several, rather like a pianist playing chords—but on an enormous keyboard. A banana, for example, contains three hundred volatiles, as the active molecules in aromas are called. Tomatoes have four hundred, coffee no fewer than six hundred. Working out how and to what degree these contribute to an aroma is not straightforward. Even at the simplest level, results are often wildly counterintuitive. If you combine the fruity odor of ethyl isobutyrate with the caramel-like allure of ethyl maltol and the violet scent of allyl alpha-ionone, you get pineapple, which smells wholly unlike its three principal inputs.
  • An interesting and important curiosity of our sense of smell is that it is the only one of the five basic senses not mediated by the hypothalamus. When we smell something, the information, for reasons unknown, goes straight to the olfactory cortex, which is nestled close to the hippocampus, where memories are shaped, and it is thought by some neuroscientists that that may explain why certain odors are so powerfully evocative of memories for us.
  • Smell is certainly an intensely personal experience. “I think the single most extraordinary aspect of olfaction is that we all smell the world differently,” Beauchamp says. “Although we all have 350 to 400 types of odor receptor, only about half of them are common to all people. That means that we don’t smell the same things.”

Down the hatch: the mouth and throat

  • Uniquely among mammals, we send our air and food down the same tunnel. Only a small structure called the epiglottis, a kind of trapdoor for the throat, stands between us and catastrophe.
  • Saliva is almost entirely water. Only 0.5 percent of it is anything else, but that tiny portion is full of useful enzymes—proteins that speed up chemical reactions. Among these are amylase and ptyalin, which begin to break down sugars in carbohydrates while they are still in our mouths. Chew a starchy food like bread or potato for a bit longer than normal and you will soon notice a sweetness. Unfortunately for us, bacteria in our mouths like that sweetness, too; they devour the liberated sugars and excrete
  • Saliva is almost entirely water. Only 0.5 percent of it is anything else, but that tiny portion is full of useful enzymes—proteins that speed up chemical reactions. Among these are amylase and ptyalin, which begin to break down sugars in carbohydrates while they are still in our mouths. Chew a starchy food like bread or potato for a bit longer than normal and you will soon notice a sweetness. Unfortunately for us, bacteria in our mouths like that sweetness, too; they devour the liberated sugars and excrete acids, which drill through our teeth and give us cavities.
  • It is nearly always wrong to talk about how food tastes, though of course we all do. What we appreciate when we eat is flavor, which is taste plus smell.
  • Smell is said to account for at least 70 percent of flavor, and maybe even as much as 90 percent.
  • sound materially influences how delicious we find food. People who are played a range of crunching sounds through headphones while sampling potato chips from various bowls will always rate the crunchier, noisier chips as fresher and tastier, even though all the chips are the same.
  • Altogether we have about ten thousand taste buds, mostly distributed around the tongue, except in the very middle, where there are none at all. Additional taste buds are found in the roof of the mouth and lower down the throat, which is said to be why some medicines taste bitter as they go down.
  • Stuttering is one of the cruelest and least understood of everyday maladies. It affects 1 percent of adults and 4 percent of children. For reasons unknown, 80 percent of sufferers are male.
  • No one knows what provokes it or why different sufferers stumble over different letters or words in different positions in a sentence. It is more common among left-handers than right-handers, especially those who have been made to write right-handed. For many, the stammering miraculously ceases when they sing the words or speak another language or talk to themselves. The majority of speakers recover from the condition by their teenage years (which is why the proportion of child sufferers is so much higher than adult ones). Females seem to recover more easily than males.

The heart and blood

  • No notes.

The chemistry department

  • Right now, about a quarter of all your blood is in your liver.

In the dissecting room: the skeleton

  • University Medical Center, Gerard Karsenty, realized that osteocalcin, which is produced in bones, not only is a hormone but seems to be involved in a large number of important regulatory activities across the body, from helping to manage glucose levels to boosting male fertility to influencing our moods and keeping our memory in working order. Apart from anything else, it could help to explain the long-standing mystery of how regular exercise helps to stave off Alzheimer’s disease: exercise builds stronger bones and stronger bones produce more osteocalcin.
  • Our feet were designed to grasp, which is why you have a lot of bones in them. They were not designed to support a lot of weight, which is one reason they ache at the end of a long day of standing or walking. As Jeremy Taylor points out in Body by Darwin, ostriches have eliminated this problem by fusing the bones of their feet and ankle, but then ostriches have had 250 million years to adjust to upright walking, roughly forty times as long as we have had.
  • All bodies are compromises between strength and mobility. The bulkier an animal is, the more massive its bones must be. So an elephant is 13 percent bone, whereas a tiny shrew needs to devote just 4 percent of itself to skeleton. Humans fall in between at 8.5 percent.
  • About 40 percent of people over seventy-five who break their hips are no longer able to care for themselves. For many, it is a kind of last straw. Ten percent die within thirty days, and nearly 30 percent die within twelve months.

On the move: bipedalism and exercise

  • The ten-thousand-step idea is often attributed to a single study done in Japan in the 1960s, though it appears that also may be a myth.
  • the Centers for Disease Control’s recommendations on exercise—namely, 150 minutes per week of moderate activity—are based not on the optimal amount needed for health, because no one can say what that is, but on what the CDC’s advisers think people will perceive as realistic goals.
  • Modern hunter-gatherers, by contrast, average about nineteen miles of walking and trotting to secure a day’s food, and it is reasonable to assume that our ancient forebears would have done about the same. In short, they worked hard for what they ate and consequently ended up with bodies designed to do two somewhat contradictory things: to be active much of the time, but never to be more active than absolutely necessary.
  • The current generation of young people is forecast to be the first in recorded history not to live as long as their parents because of weight-related health issues.
  • One big problem with exercise is that we don’t track it very scrupulously. One study in America found that people overestimate the number of calories they burned in a workout by a factor of four. They also then consumed, on average, about twice as many calories as they had just burned off.
  • worker on a factory floor will in a year expend about 175,000 more calories than a desk worker—equivalent to more than sixty marathons.
  • you should get up and move around a little. According to one study, being a committed couch potato (defined as someone who sits for six hours or more per day) increases the mortality risk for men by nearly 20 percent and for women by almost double that. (Why sitting too much is so much more dangerous for women is unclear.) People who sit a lot are twice as likely to contract diabetes, twice as likely to have a fatal heart attack, and two and a half times as likely to suffer cardiovascular disease.
  • If you spend an evening on the seductive padding of your gluteus maximus, you may nullify any benefits you gained during an active day. As James Hamblin put it in The Atlantic, “You can’t undo sitting.”

Equilibrium

  • One area where animals are curiously—almost eerily—uniform is with the number of heartbeats they have in a lifetime. Despite the vast differences in heart rates, nearly all animals have about 800 million heartbeats in them if they live an average life. The exception is humans. We pass 800 million heartbeats after twenty-five years, and just keep on going for another fifty years and 1.6 billion heartbeats or so.
  • our body temperature is elevated beyond normal in the condition known as a fever. Curiously, no one knows quite why this happens—whether fevers are an innate defense mechanism aimed at killing invading pathogens or simply a by-product of the body working hard to fight off infection. The question is important because if fever is a defense mechanism, then any effort to suppress or eliminate it may be counterproductive. Allowing a fever to run its course (within limits, needless to say) could be the wisest thing.
  • we are powerfully dependent on ATP to keep our cells humming. Every day you produce and consume your own body weight in ATP—some 200 trillion trillion molecules of it. From ATP’s point of view, you are really just a machine for producing ATP. Everything else about you is by-product. Because ATP is consumed more or less instantaneously, you have only sixty grams—that is a little over two ounces—of it within you at any given moment.
  • we are the size we are because that is about the only size we can be.

The immune system

  • Allergy rates vary across the world from about 10 to 40 percent, with the rates closely following economic performance. The richer the country, the more allergies its citizens get. No one knows why being rich should be so bad for you. It may be that people of rich, urbanized nations are more exposed to pollutants—there is evidence that nitrogen oxides from diesel fuels correlate with higher incidences of allergies—or it may be that increased use of antibiotics in the rich nations has directly or indirectly affected our immune responses.

Deep breath: the lungs and breathing

  • The diaphragm is a mammalian invention and it is a good one. By pulling down on the lungs from below, it helps them to work more powerfully. The increased respiratory efficiency that the diaphragm brings enables us to get more oxygen to our muscles, which helped us to become strong, and to our brains, which helped us to become smart.
  • If you are an averagely sized adult, you will have roughly twenty square feet of skin, but about a thousand square feet of lung tissue containing about fifteen hundred miles of airways. Packing such a lot of breathing apparatus into the modest space of your chest is a nifty solution to the very considerable problem of how to get a lot of oxygen efficiently to billions of cells.
  • Globally, asthma is more common among boys than girls before puberty, but more common in girls than boys after puberty. It is more common in blacks than whites (generally but not everywhere) and in city people than rural people. In children, it is closely associated with both being obese and being underweight; obese children get it more often, but underweight children get it worse. The highest rate in the world is in the U.K., where 30 percent of children have shown asthma symptoms. The lowest rates are in China, Greece, Georgia, Romania, and Russia, with just 3 percent. All the English-speaking nations of the world have high rates, as do those of Latin America. There is no cure, though in 75 percent of young people asthma resolves itself by the time they reach early adulthood. No one knows how or why that happens either, or why it doesn’t happen for the unfortunate minority. Indeed, where asthma is concerned, no one knows much of anything.
  • people who had had a cat early in life seemed to derive lifelong protection from getting asthma.
  • asthma was a rare disease and not well understood. Today it is common and still not understood.
  • asthma remains the fourth leading cause of childhood death in Britain. In the United States, between 1980 and 2000 asthma rates doubled, but hospitalization rates tripled, suggesting that asthma is now not only more common but more severe. Similar rises have been found throughout much of the developed world—in Scandinavia, Australia, New Zealand, some of the richer parts of Asia—but not, curiously, everywhere. Japan, for instance, has not seen a great increase in asthma rates.
  • Asthma is very different from other lung disorders in that it is normally present only some of the time. “If you test the lung function of asthmatics, most of the time for most of them it will be completely normal. It’s only when they have an attack that problems with lung function become apparent and detectable. That’s very unusual for a disease.
  • “For a long time,” he told me when we met, “the dogma was that asthma was a neurological disease—the nervous system sending the wrong signals to the lungs. Then, in the 1950s and ’60s, the idea came along that it is an allergic reaction, and that has pretty much stuck. […] now we are coming full circle for at least part of the answer.” […] “All we can really say about asthma is that it is primarily a Western disease,”
  • “Doctors will tell you that the first few years of life are crucial for asthma, but that’s not exactly true,” says Pearce. “It’s the first few years of exposure. If you change jobs or change countries, you can still get asthma even as an adult.”
  • In what way exactly Western lifestyles might provoke asthma isn’t easy to say. Growing up on a farm seems to protect you, and moving to the city increases your risk, but once again we don’t really know why.
  • Children who sit watching television not only are not exercising their lungs as they would if they were at play but even breathe differently from children who are not transfixed by a screen. Specifically, children who are reading take deeper breaths and sigh more often than children watching TV, and that slight difference in respiratory activity may be enough to increase TV watchers’ susceptibility to asthma,
  • If you do get hiccups and they don’t go away spontaneously after a few minutes, medical science is at a more or less complete loss to help you. The best remedies any doctor can suggest are the same ones you’ve known about since you were small: startling the victims (by sneaking up and going, “Boo!” say), rubbing the back of their neck, having them take a bite of a lemon or a big sip of iced water or pulling on their tongues, and at least a dozen others. Whether any of these age-old remedies actually work is not a matter medical science has addressed.

Food, glorious food

  • many nuts, for instance, are less completely digested than other foods, which means that they leave behind fewer calories than are consumed. You may eat 170 calories’ worth of almonds, but keep only 130 of them.
  • Vitamins are simply organic chemicals—that is, from things that are or were once alive, like plants and animals—while minerals are inorganic and come from soil or water. Altogether there are about forty of these little particles that we must get from our foods because we cannot manufacture them for ourselves.
  • Of all the many things we take in with our foods (salts, water, minerals, and so on), just three need to be altered as they proceed through the digestive tract: proteins, carbohydrates, and fats.
  • Eight of the twenty amino acids cannot be made in the body and must be consumed in the diet.*2 If they are missing from the foods we eat, then certain vital proteins cannot be made. Protein deficiency is almost never a problem for people who eat meat, but it can be for vegetarians because not all plants provide all the necessary amino acids. It is interesting that most traditional diets in the world are based around combinations of plant products that do provide all the necessary amino acids. So people in Asia eat a lot of rice and soybeans, while indigenous Americans have long combined corn with black or pinto beans. This isn’t just a matter of taste, it seems, but an instinctive recognition of the need for a rounded diet.
  • One other enduring myth concerning water intake is the belief that caffeinated drinks are diuretics and make you pee out more than you have taken in. They may not be the most wholesome of options for liquid refreshment, but they do make a net contribution to your personal water balance.
  • The French, for example, eat more cheese and drink more wine than almost anybody else on Earth and yet have some of the lowest rates of heart disease. This “French paradox,” as it is known
  • A meta-analysis at McMaster University in Canada of 133,000 people in four dozen countries found a link between high salt intake and heart problems only for those with existing hypertension, while low salt intake (less than three thousand milligrams a day) had an increased risk of heart problems for people from both groups. In other words, according to the McMaster study, too little salt is at least as risky as too much.
  • “Lots of food products are advertised as low in salt, fat, or sugar, but nearly always when manufacturers reduce one of the three, they boost the other two to compensate.

The guts

  • Men and women evince a surprising amount of difference in this regard. For a man, the average journey time from mouth to anus is fifty-five hours. For a woman, typically, it is more like seventy-two. Food lingers inside a woman for nearly a full day longer, with what consequences, if any, we do not know.
  • The largest source of foodborne illness is not meat or eggs or mayonnaise, as commonly supposed, but green leafy vegetables. They account for one in five of all food illnesses.
  • The smell of a fart is composed largely of hydrogen sulfide, even though hydrogen sulfide accounts for only about one to three parts per million of what is expelled. Hydrogen sulfide in concentrated form—as in sewage gas—can be highly lethal, but why we are so sensitive to it in trace exposures is a question science has yet to answer. Curiously, we don’t smell it at all when it rises to lethal levels.
  • E. coli is a strange organism in that most strains do us no harm and some are positively beneficial—so long as they don’t end up in the wrong place. E. coli in your colon, for instance, produces vitamin K

Sleep

  • One curious fact is that animals that are hibernating also have periods of sleep. It comes as a surprise to most of us, but hibernation and sleep are not the same thing at all, at least not from a neurological and metabolic perspective. Hibernating is more like being concussed or anesthetized: the subject is unconscious but not actually asleep.
  • our eyes contain a third photoreceptor cell type in addition to the well-known rods and cones. These additional receptors, known as photosensitive retinal ganglion cells, have nothing to do with vision but exist simply to detect brightness—to know when it is daytime and when night. They pass this information on to two tiny bundles of neurons within the brain, roughly the size of a pinhead, embedded in the hypothalamus and known as suprachiasmatic nuclei. These two bundles (one in each hemisphere) control our circadian rhythms.
  • “What’s really interesting about these third receptors,” Foster told me when we met in his office at Brasenose College, just off the High Street, “is that they function completely independently of sight. As an experiment, we asked a lady who was completely blind—she had lost her rods and cones as a result of a genetic disease—to tell us when she thought the lights in the room were switched on or off. She told us not to be ridiculous because she couldn’t see anything, but we asked her to try anyway. It turned out she was right every time. Even though she had no vision—no way of ‘seeing’ the light—her brain detected it with perfect fidelity at a subliminal level.
  • Melatonin levels within us rise as evening falls and peak in the middle of the night, so it would seem logical to associate them with drowsiness, but in fact melatonin production also rises at night in nocturnal animals when they are most active, so it is not promoting sleepiness. The pineal, in any case, tracks not just day/night rhythms but also seasonal changes, which are really important for animals that hibernate or breed seasonally.
  • our teeth mark the passing of time by acquiring daily microscopic accretions, not unlike tree rings, until they stop growing at about the age of twenty.

Into the nether regions

  • As Siddhartha Mukherjee observed in The Gene: An Intimate History, humans don’t actually reproduce at all. Geckos reproduce; we recombine.

In the beginning: conception and birth

  • most miscarriages and other setbacks in pregnancy are because of problems with the placenta, not the fetus. Much of this is not well understood.
  • We don’t know what triggers birth. Something must count down the 280 days of human gestation, but no one has worked out where and what that mechanism is or what makes its alarm go off. All that is known is that the body begins to produce hormones called prostaglandins, which normally are involved in dealing with injuries to tissue but now activate the uterus, which begins a series of increasingly painful contractions to move the baby into position for birth.
  • Various studies have found that people born by C-section have substantially increased risks for type 1 diabetes, asthma, celiac disease, and even obesity and an eightfold greater risk of developing allergies. Cesarean babies eventually acquire the same mix of microbes as those born vaginally—by a year their microbiota are usually indistinguishable—but there is something about those initial exposures that makes a long-term difference.
  • As well as nurturing symbiotic bacteria, breast milk is full of antibodies. There is some evidence that a nursing mother absorbs a little of her suckling baby’s saliva through her breast ducts and that this is analyzed by her immune system, which adjusts the amount and types of antibodies she supplies to the baby, according to its needs.
  • the Barker hypothesis or, a little less snappily, the theory of fetal origins of adult disease. Barker, an epidemiologist, posited that what happens in the womb can determine health and well-being for the rest of one’s life. “For every organ, there is a critical period, often very brief, when it goes through development,” he said not long before his death in 2013. “It happens for different organs at different times. After birth only the liver and the brain and the immune system remain plastic. Everything else is done.”
  • Most authorities now extend that period of crucial vulnerability from the moment of your conception to your second birthday—what has become known as the first thousand days.

Nerves and pain

  • The experience of pain begins just beneath the skin in specialized nerve endings known as nociceptors. (“Noci-” is from a Latin word meaning “hurt.”) Nociceptors respond to three kinds of painful stimuli: thermal, chemical, and mechanical,
  • Sherrington’s landmark book on the subject, The Integrative Action of the Nervous System, has been compared to Newton’s Principia and Harvey’s De motu cordis (On the Motion of the Heart) in terms of its revolutionary importance to its field.
  • “The drugs we have relieve 50 percent of pain in somewhere between one in four and one in seven of the patients we treat. That’s for the best drugs.” In other words, some 75 percent to 85 percent of people get no benefit at all from even the best pain drugs, and those who do get benefit don’t usually get much.
  • people given a colored tablet with corners will report feeling better than when given a plain white tablet. Red pills are deemed more fast acting than white pills. Green and blue pills have a more soothing effect. Patrick Wall, in his book on pain, reported how one doctor got good results from handing his patients pills held in a forceps, explaining that they were too potent to be held by bare fingers. Extraordinarily, placebos are even effective when people know they are placebos.
  • Being depressed or worried will almost always increase perceived levels of pain. But equally pain is decreased by pleasant aromas, soothing images, pleasurable music, good food, and sex. Just having a sympathetic and loving partner cuts the reported pain of angina by half, according to one study. Expectation is hugely important, too. In one experiment done by Tracey and her team, when subjects in pain received morphine without being told, its analgesic effects were greatly lessened. In many ways, we feel the pain we expect to feel.

When things go wrong: diseases

  • A second category of disorders that have become more common in modern times, and represent a much greater risk for most of us, is what Professor Daniel Lieberman of Harvard calls mismatch diseases—that is, diseases brought on by our indolent and overindulgent modern lifestyles. The idea, roughly, is that we are born with the bodies of hunter-gatherers but pass our lives as couch potatoes.
  • Two types of diseases in particular are more visible now than they were in times past, in part at least because we aren’t being killed off by other things first.
  • One is genetic diseases. Twenty years ago, about five thousand genetic diseases were known. Today it is seven thousand. The number of genetic diseases is constant. What has changed is our ability to identify them.
  • When talking of diseases, people often use “infectious” and “contagious” interchangeably, but there is a difference. An infectious disease is one caused by a microbe; a contagious disease is one transmitted by contact.
  • Every February, the World Health Organization and the Centers for Disease Control get together and decide what to make the next flu vaccine from, usually based on what’s going on in eastern Asia.
  • Based on all the available information, the WHO and CDC announce their decision on February 28, and all the flu vaccine manufacturers in the world begin working on the same strain.

When things go very wrong: cancer

  • if all men lived long enough, they would all get prostate cancer.
  • six attributes in particular that all cancer cells have, namely: They divide without limit. They grow without direction or influence from outside agents like hormones. They engage in angiogenesis, which is to say they trick the body into giving them a blood supply. They disregard any signals to stop growing. They fail to succumb to apoptosis, or programmed cell death. They metastasize, or spread to other parts of the body.
  • Cancer is above all an age thing. Between birth and the age of forty, men have just a one in seventy-one chance of getting cancer and women one in fifty-one, but over sixty the odds drop to one in three for men and one in four for women. An eighty-year-old person is a thousand times more likely than a teenager to develop cancer.
  • Lifestyle is a huge factor in determining which of us get cancer. More than half of cases, by some calculations, are caused by things we can do something about—smoking, drinking to excess, and overeating primarily.
  • “If one asks the question what are the ten most abundant molecules in the human habitat, no one can answer.” Of the things that might harm us, only radon, carbon dioxide, tobacco smoke, and asbestos have been studied really extensively. The rest is mostly speculation.
  • More than eighty thousand chemicals are produced commercially in the world today, and by one calculation 86 percent of them have never been tested for their effects on humans.

Medicine good and bad

  • life expectancy on Earth improved by as much in the twentieth century as in the whole of the preceding eight thousand years.
  • the leading causes of death recorded on mortality tables—heart attacks, diabetes, cancer, and so on—were very often outcomes of other conditions and that the real causes were factors like smoking, poor diet, illicit use of drugs, and other behaviors overlooked on death certificates.
  • “At some point between 1900 and 1912, a random patient with a random disease, consulting a doctor chosen at random, had for the first time in history a better than fifty-fifty chance of profiting from the encounter.”
  • medicine could account for no more than perhaps 20 percent of the improvements. All the rest were the result of improved sanitation and diet, healthier lifestyles, and even things like the rise of the railways, which improved food distribution, bringing fresher meat and vegetables to city dwellers.
  • Climb aboard a bus or subway train in almost any large city in the Western world and you can experience similar vast disparities with a short journey. In Paris, travel five stops on the Metro’s B line from Port-Royal to La Plaine—Stade de France and you will find yourself among people who have an 82 percent greater chance of dying in a given year than those just down the line. In London, life expectancy drops reliably by one year for every two stops traveled eastward from Westminster on the District Line of the Underground. In St. Louis, Missouri, make a twenty-minute drive from prosperous Clayton to the inner-city Jeff-Vander-Lou neighborhood and life expectancy drops by one year for every minute of the journey, a little over two years for every mile.
  • If you are middle-aged, exceptionally well-off, and from almost any high-income nation, the chances are excellent that you will live into your late eighties. Someone who is otherwise identical to you but poor—exercises as devotedly, sleeps as many hours, eats a similarly healthy diet, but just has less money in the bank—can expect to die between ten and fifteen years sooner. That’s a lot of difference for an equivalent lifestyle, and no one is sure how to account for it.
  • health deficits begin at birth and go right on through life. Children in the United States are 70 percent more likely to die in childhood than children in the rest of the wealthy world. Among rich countries, America is at or near the bottom for virtually every measure of medical well-being—for chronic disease, depression, drug abuse, homicide, teenage pregnancies, HIV prevalence. Even sufferers of cystic fibrosis live ten years longer on average in Canada than in the United States.
  • “Even wealthy Americans are not isolated from a lifestyle filled with oversized food portions, physical inactivity, and stress.” The average Dutch or Swedish citizen consumes about 20 percent fewer calories than the average American, for instance. That doesn’t sound massively excessive, but it adds up to 250,000 calories over the course of a year. You would get a similar boost if you sat down about twice a week and ate an entire cheesecake.
  • The upshot is that Australia, New Zealand, the Nordic countries, and the wealthier nations of the Far East all do really well, and other European nations do pretty well. For the United States, the result is, at best, decidedly mixed. For Britain, cancer survival rates are grim and ought to be a matter of national concern.
  • Other factors can significantly affect outcomes, sometimes in surprising ways. Just being kind, for instance. A study in New Zealand of diabetic patients in 2016 found that the proportion suffering severe complications was 40 percent lower among patients treated by doctors rated high for compassion. As one observer put it, that is “comparable to the benefits seen with the most intensive medical therapy for diabetes.”

The end

  • In 2011, an interesting milestone in human history was passed. For the first time, more people globally died from non-communicable diseases like heart failure, stroke, and diabetes than from all infectious diseases combined. We live in an age in which we are killed, more often than not, by lifestyle. We are in effect choosing how we shall die, albeit without much reflection or insight.
  • About one-fifth of all deaths are sudden, as with a heart attack or car crash, and another fifth come quickly, following a short illness. But the great majority, about 60 percent, are the result of a protracted decline.
  • we have reached a point of diminishing returns. By one calculation, if we found a cure for all cancers tomorrow, it would add just 3.2 years to overall life expectancy. Eliminating every last form of heart disease would add only 5.5 years. That’s because people who die of these things tend to be old already, and if cancer or heart disease doesn’t get them, something else will.
  • Free radicals are wisps of cellular waste that build up in the body in the process of metabolism. They are a by-product of our breathing oxygen. As one toxicologist has put it, “The biochemical price of breathing is aging.”
  • sheep are almost the only land-based creatures known to experience menopause, too. At least two species of whales also go through it. Why any animals get it is a question yet to be answered.
  • A STUDY BY the Albert Einstein College of Medicine in New York in 2016 concluded that however much medical care may advance, it is unlikely that many people will ever live past about 115 years.
  • people in one of the poorest regions of Costa Rica, the Nicoya Peninsula, live longest of all, even though they have much higher rates of obesity and hypertension. They also have longer telomeres. The theory is that they benefit from closer social bonds and family relationships. Curiously, it was found that if they live alone or don’t see a child at least once a week, the telomere length advantage vanishes. It is an extraordinary fact that having good and loving relationships physically alters your DNA.