Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping

by Robert M. Sapolsky

the best way to begin is by making a mental list of the sorts of things we find stressful. No doubt you would immediately come up with some obvious examples—traffic, deadlines, family relationships, money worries. But what if I said, “You’re thinking like a speciocentric human. Think like a zebra for a second.” Suddenly, new items might appear at the top of your list—serious physical injury, predators, starvation.

Essentially, we humans live well enough and long enough, and are smart enough, to generate all sorts of stressful events purely in our heads. How many hippos worry about whether Social Security is going to last as long as they will, or what they are going to say on a first date?

A stressor is anything in the outside world that knocks you out of homeostatic balance, and the stress-response is what your body does to reestablish homeostasis.

when we get into a physiological uproar and activate the stress-response for no reason at all, or over something we cannot do anything about, we call it things like “anxiety,” “neurosis,” “paranoia,” or “needless hostility.” Thus, the stress-response can be mobilized not only in response to physical or psychological insults, but also in expectation of them.

Thus, during stress, digestion is inhibited—there isn’t enough time to derive the energetic benefits of the slow process of digestion, so why waste energy on it? You have better things to do than digest breakfast when you are trying to avoid being someone’s lunch. The same thing goes for growth and reproduction, both expensive, optimistic things to be doing with your body (especially if you are female).

During stress, growth and tissue repair is curtailed, sexual drive decreases in both sexes; females are less likely to ovulate or to carry pregnancies to term, while males begin to have trouble with erections and secrete less testosterone.

The immune system, which defends against infections and illness, is ideal for spotting the tumor cell that will kill you in a year, or making enough antibodies to protect you in a few weeks, but is it really needed this instant? The logic here appears to be the same—look for tumors some other time; expend the energy more wisely now.

Energy is mobilized and delivered to the tissues that need them; long-term building and repair projects are deferred until the disaster has passed.

If you repeatedly turn on the stress-response, or if you cannot turn off the stress-response at the end of a stressful event, the stress-response can eventually become damaging.

recent findings that sustained exposure to certain of the hormones secreted during stress may actually accelerate the aging of the brain.

if you want to increase your chances of avoiding stress-related diseases, make sure you don’t inadvertently allow yourself to be born poor.

You sit in your chair not moving a muscle, and simply think a thought, a thought having to do with feeling angry or sad or euphoric or lustful, and suddenly your pancreas secretes some hormone.

When something stressful happens or you think a stressful thought, the hypothalamus secretes an array of releasing hormones into the hypothalamic-pituitary circulatory system that gets the ball rolling.

Glucocorticoids, glucagon, and the sympathetic nervous system raise circulating levels of the sugar glucose. As we will see, these hormones are essential for mobilizing energy during stress.

The secretion of various reproductive hormones such as estrogen, progesterone, and testosterone is inhibited.

Taylor suggests that rather than the female stress-response being about fight-or-flight, it’s about “tend and befriend”—taking care of her young and seeking social affiliation.

And the fact that oxytocin is secreted during stress in females supports the idea that responding to stress may not just consist of preparing for a mad dash across the savanna, but may also involve feeling a pull toward sociality.

Sympathetic arousal is a relative marker of anxiety and vigilance, while heavy secretion of glucocorticoids is more a marker of depression.

Tissues in various parts of the body may be altered in their sensitivity to a stress hormone in the case of one stressor, but not the other.

When the man sat quietly, his gut tissues were bright pink, well supplied with blood. Whenever he became anxious or angry, the gut mucosa would blanch, because of decreased blood flow.

CRP is turning out to be a much better predictor of cardiovascular disease risk than cholesterol, even years in advance of disease onset.

if you couple the social stress with a high-fat diet, the effects synergize, and plaque formation goes through the roof.

and you get claudication, which means that your legs and chest hurt like hell for lack of oxygen and glucose whenever you walk; you are then a candidate for bypass surgery.

Whenever you inhale, you turn on the sympathetic nervous system slightly, minutely speeding up your heart. And when you exhale, the parasympathetic half turns on, activating your vagus nerve in order to slow things down (this is why many forms of meditation are built around extended exhalations). Therefore, the length of time between heartbeats tends to be shorter when you’re inhaling than exhaling. But what if chronic stress has blunted the ability of your parasympathetic nervous system to kick the vagus nerve into action?

your sympathetic nervous system probably has roughly the same effect on your coronary arteries whether you are in the middle of a murderous rage or a thrilling orgasm. Diametrically opposite emotions then can have surprisingly similar physiological underpinnings

“The opposite of love is not hate. The opposite of love is indifference.”).

The official numbers are that stress makes about two-thirds of people hyperphagic (eating more) and the rest hypophagic.

It turns out that we also differ as to how readily we store food away after a stressor. And where in the body we store it.

fat cells located in your abdominal area, around your belly, are known as “visceral” fat. Fill up those fat cells with fat, without depositing much fat elsewhere in your body, and you take on an “apple” shape.

it’s the apples who are at risk for metabolic and cardiovascular disease. Among other reasons, this is probably because fat released from abdominal fat cells more readily finds its way to the liver (in contrast to fat from gluteal fat stores, which gets dispersed more equally throughout the body), where it is converted into glucose, setting you up for elevated blood sugar and insulin resistance.

suppose you feel terrible, something isn’t working right, and the docs can’t find a thing wrong. Congratulations, you now have a “functional” GI disorder. These are immensely sensitive to stress.

The most common functional GI disorder, which will be considered here, is irritable bowel syndrome (IBS), which involves abdominal pain (particularly just after a meal) that is relieved by defecating and symptoms such as diarrhea or constipation, passage of mucus, bloating, and abdominal distention.

Carefully conducted studies show that major chronic stressors increase the risk of the first symptoms of IBS appearing, and worsen preexisting cases.

IBS—also known as “spastic colon”—involves the colon being too contractile, an excellent way of producing diarrhea. (It is not clear why lots of stress-induced contractions of the colon can lead to constipation. As a possible explanation, the stress-induced contractions in the colon are directional, which is to say, they push the contents of the colon from the small intestinal end to the anus. And if they do that a lot, things get accelerated, resulting in diarrhea. However, in one plausible scenario, with long enough periods of stress, the contractions begin to get disorganized, lose their directionality, so that not much of anything moves toward the anus).

a person with IBS is subjected to a controlled stressor (keeping her hand in ice water for a while, trying to make sense of two recorded conversations at once, participating in a pressured interview). Contractions in the colon increase in response to these stressors more in IBS patients than in control subjects.

stress can blunt the sort of pain you feel in your skin and skeletal muscles while increasing the sensitivity of internal organs like the intestines to pain (something called “visceral” pain).

just to make the whole process worse, the pain of that gassy, distended, hypersensitive gut can stimulate sympathetic activation even further, making for a vicious circle.

An ulcer is a hole in the wall of an organ, and ulcers originating in the stomach or in the organs immediately bordering it are termed peptic ulcers. The ones within the stomach are called gastric ulcers; those a bit higher up than the stomach are esophageal, and those at the border of the stomach and the intestine are duodenal (the most common of peptic ulcers). Photomicrograph of a stomach ulcer.

the damage occurs not during the period of stress but in its aftermath, and not so much because stress increases the size of an insult (for example, the amount of acid secreted or the amount of oxygen radicals produced), but because, during the stressful emergency, the gut scrimps on defenses against such insults.

if you lose a parent to death while you are a child, your risk of major depression has increased for the rest of your life.

Consider a female who is pregnant during a famine. She’s not getting enough calories, nor is her fetus. It turns out that during the latter part of pregnancy, a fetus is “learning” about how plentiful food is in that outside world, and a famine winds up “teaching” it that, jeez, there’s not a whole lot of food out there, better store every smidgen of it.

Everything else being equal throughout life, even late in life, that organism is more at risk for hypertension, obesity, adult-onset diabetes, and cardiovascular disease.

Prenatally stressed rats, as adults, freeze up when around bright lights, can’t learn in novel settings, defecate like crazy.

anxiety revolves around a part of the brain called the amygdala, and prenatal stress programs the amygdala into a lifelong profile that has anxiety written all over it.

The stress dwarfism is not a problem of insufficient food—the boy was eating more at the time he entered the hospital than a few months later, when his growth resumed.

You can’t ask for a clearer demonstration that what is going on in our heads influences every cell in our bodies.

Touch is one of the central experiences of an infant.

New bone is constantly being formed, in much the same way as in a teenager. Old bone is being broken down, disintegrated by ravenous enzymes (a process called resorption).

work from Jay Kaplan’s group has shown that chronic social stress leads to loss of bone mass in female monkeys.

Males who do extreme amounts of exercise, such as professional soccer players and runners who cover more than 40 or 50 miles a week, have less LHRH, LH, and testosterone in their circulation, smaller testes, less functional sperm.