By John Carpi, published on January 1, 1996 - last reviewed on November 22, 2010
Psychological stress doesn't just put your head in a vice. New studies document exactly how it tears away at every body system—including your brain. But get this: The experience of stress in the past magnifies your reactivity to stress in the future. So take a nice deep breath and find a stress-stopping routine this instant.
Technological advances have expanded the business day. Leisure time has shrunk. Bathing-suited business men walk beaches on Sundays with cellular phones stuck to their ears, planning the next morning's meetings. Laptop computers find their way on vacations. The family icons of today are working couples picking up their children on their way home to dinners prepared by caterers or fast food chefs. Grieving time has shrunk. The divorce rate hovers near its highest in history. The concept of job security has gone the way of the dirigible. Yet there is no time to pick up the pieces. "Just snap out of it," yells the therapist as he slaps his patient in a newspaper cartoon. The caption: Time-saving single-visit psychotherapy.
Stress has become so endemic it is worn like a badge of courage. The business of stress reduction, from workshops to relaxation tapes to light and sound headsets, is booming. If ours is a culture without deep intimacy, then our relationship with stress is the exception.
Yet not even this familiarity can cushion the findings of research: The effects of stress are even more profound than imagined. It penetrates to the core of our being. Stress is not something that just grips us and, with time or effort, then lets go. It changes us in the process. It alters our bodies—and our brains.
We may respond to stress as we do an allergy. That is, we can become sensitized, or acutely sensitive, to stress. Once that happens, even the merest intimation of stress can trigger a cascade of chemical reactions in brain and body that assault us from within. Stress is the psychological equivalent of ragweed. Once the body becomes sensitized to pollen or ragweed, it takes only the slightest bloom in spring or fall to set off the biochemical alarm that results in runny noses, watery eyes, and the general misery of hay fever. But while only some of us are genetically programed to be plagued with hay fever, all of us have the capacity to become sensitized to stress.
Stress sensitization is uncharitably subversive. While the chemical signaling systems of body and brain are running amok in a person sensitized to stress, that person's perception of stress remains unchanged. It's as if the brain, aware that the burner on the stove is cool, still signals the body to jerk its hand away. "What happens is that sensitization leads the brain to re-circuit itself in response to stress," says psychologist Michael Meaney, Ph.D., of McGill University. "We know that what we are encountering may be a normal, everyday episode of stress, but the brain is signaling the body to respond inappropriately." We may not think we are getting worked up over running late for an appointment, but our brain is treating it as though our life were on the line.
Because some stress is absolutely necessary in living creatures, everyone has a built-in gauge that controls our reaction to it. It's a kind of biological thermostat that keeps the body from launching an all-out response literally over spilled milk. Sensitization, however, lowers the thermostat's set point, says psychologist Jonathan C. Smith, Ph.D., founder and director of the Stress Institute at Roosevelt University in Chicago. As a result, the body response typically reserved for life-threatening events is turned on by life's mundane aggravations. In this hothouse of hyperreactivity, bio-chemicals unleashed by stress may boil over at the most trivial of events, like our missing a train or being shunted to voice mail.
"Years of research has told us that people do become sensitized to stress and that this sensitization actually alters physical patterns in the brain," says Seymour Levine, Ph.D., of the University of Delaware. "That means that once sensitized, the body just does not respond to stress the same way in the future. We may produce too many excitatory chemicals or too few calming ones; either way we are responding inappropriately."
The revelation that stress itself alters our ability to cope with stress has produced yet another remarkable finding: Sensitization to stress may occur before we are old enough to prevent it ourselves. New studies suggest that animals from rodents to monkeys to humans may experience still undetermined developmental periods during which exposure to stress is more damaging than in later years. "For example, we have known that losing a parent when you are young is harder to get over than if your parent dies when you are an adult," says Jean King, Ph.D., of the University of Massachusetts Medical School. "What we now believe is that a stress of that magnitude occurring when you are young may permanently rewire the brain's circuitry, throwing the system askew and leaving it less able to handle normal, everyday stress."
It is the stew of chemicals released by such provocations that ultimately explains the noose stress ties between mind and body. "This new paradigm of stress demonstrates that there is a link between psychological events and physical eruptions, between mind and body," King says. "The psychological events that are most deleterious probably occur during infancy and childhood—an unstable home environment, living with an alcoholic parent, or any other number of extended crises." The new paradigm also firmly ties everyday psychological stress to such suspect complaints as ulcers, headaches, and fatigue.
The new blueprint of how we respond to stress also may explain why people have different tolerances for stress. In the past stress tolerance may have been chalked up to mental fortitude: "He's a rock," or "She's really bearing up under pressure." Now it's clear that our ability to withstand stress has less to do with whether we are strong-willed than with how much and what kind of stress we encountered in the past.
Whether we end up stressed-out executives or laid-back surfers, we all start out with the same biological machinery for responding to stress. Stress activates primitive regions of the brain, the same areas that control eating, aggression, and immune response. It switches on nerve circuits that ignite the body's fight-or-flight response as if there were a life-threatening danger.
From this evidence researchers have concluded that the stress response is "wired" into the brain, that we inherit the same ancient reactions that jump-started hunter-gatherers to escape a charging saber-tooth tiger without having to give their actions time-consuming thought. Only this same life-or-death reaction is now called into play largely by non-life-threatening situations. Studies have found the same fight-or-flight circuits all working overtime in response to such varied stressors as extreme exercise, the death of a loved one, an approaching deadline.
One conclusion from the evidence is that we may be victims of evolution, hard-wired with a stress response system that's better suited to a life filled with occasional life-threatening events than one filled with everyday irritations like failing a test or blowing a sales call. Unfortunately, when stresses become routine, the constant biochemical pounding takes its toll on the body; the system starts to wear out at an accelerated rate.
By responding to the stress of everyday life with the same surge of biochemicals released during major threats, the body is slowly killing itself. The biochemical onslaught chips away at the immune system, opening the way to cancer, infection, and disease. Hormones unleashed by stress eat at the digestive tract and lungs, promoting ulcers and asthma. Or they may weaken the heart, leading to strokes and heart disease. "Chronic stress is like slow poison," King observes. "It is a fact of modern life that even people who are not sensitized to stress are adversely affected by everything that can go wrong in the day."
If stress has a central command post, it is the hypothalamus, a primitive area of the brain located near where the spine runs into the skull. By way of a dazzling array of hormonal signals, the hypothalamus is closely connected with the nearby pituitary gland and the distant adrenal glands, perched atop the kidneys. The so-called hypothalamicpituitary axis (HPA) has a virtual monopoly on basic body functions. It regulates blood pressure, heart rate, body temperature, sleep patterns, hunger and thirst, and reproductive functions, among many other activities.
About the size of a grape, the hypothalamus does its work by releasing two types of signaling hormones; those that stimulate glands to release other hormones and those that inhibit the glands from performing their job. Among the best known of these hormones are follicle-stimulating and luteinizing hormones, which, dispatched on a strict schedule from the pituitary, begin the monthly process that prepares women for pregnancy or menstruation.
Like a cherry attached by its stem, the pituitary gland hangs off the hypothalamus waiting to receive instructions on which of its many hormones to release and in what quantity. In hormonal terms it is the little gland that could. The pituitary releases substances that regulate growth, sex, skin color, bone length, and muscle strength. It also releases adrenocorticotropin, a hormone that activates the third part of the body's stress system, the adrenal glands.
When stress sets off the usual ferocious communication between the hypothalamus and the pituitary, the buck stops at the adrenal glands. They manufacture and release the true stress hormones—dopamine, epinephrine (also known as adrenaline), norepinephrine (noradrenaline), and especially cortisol. So responsive to the adrenal hormones are basic body functions like blood flow and breathing that even minute changes in levels of these substances can significantly affect health.
Slight overproduction of dopamine can constrict blood vessels and raise blood pressure; a shift in epinephrine could precipitate diabetes, or asthma, by constricting tiny airways in the lungs. If the adrenal gland slacks off on cortisol production the result may be obesity, heart disease, or osteoporosis; too much of the hormone can cause women to take on masculine traits like hair growth and muscle development and lead to one of the greatest fears of all for aging men—baldness. High levels of cortisol also may kill off brain cells crucial for memory.
The adrenal gland is also home of the grand daddy of all stress reactions, the fight-or-flight response. Sensing impending danger the hypothalamus presses out cortisol-releasing factor, a hormone that prompts the pituitary gland to release adrenocorticotropin (ACTH). Carried in the bloodstream to the adrenal glands, ACTH triggers production of cortisol and epinephrine. The end result of this hormonal relay is a sudden surge in blood sugar, heart rate, and blood pressure—everything the body needs to flee or confront the imminent danger.
The problem is, what we call the stress system is actually responsible for coordinating much more than just our response to stress. "Initiating a response to stress is just one of many things the system controls," says Jean King. "These hormones are carefully regulated substances that direct everything from the immune system to the cardiovascular system to our behavioral system."
For example, cortisol directly impacts storage of short-term memory in the hippocampus. The stress hormones dopamine and epinephrine are also neurotransmitters widely active in enabling communication among brain cells. Directly and indirectly, they act on numerous neural networks in the brain and throw off levels of other neurotransmitters. Stress, it's now known, alters serotonin pathways. And through effects on serotonin, stress is now linked with depression on one hand, aggression on the other.
The developing picture of the biochemistry of stress in some ways takes the heat off psychology. "We used to say that physical manifestations of stress were psychological defense mechanisms employed as a way to shield the person from revisiting a particularly troubling event in their past," says Roosevelt's Smith. "What is far more likely is that the same chemicals being released in response to stress are triggering physical reactions throughout the body."
A torrent of studies catalogue how even a little stress can have wide-ranging effects on the body. Researchers have found that:
By charting the pathways stress hormones take throughout the body, biological cartographers are doing more than mapping the links between stress and disease. Having caught cascades of biochemicals in flagrante delicto, researchers are diagramming the exact lines of communication between mind and body. Ultimately, they will force us to erase the dividing line between what is biological and what is psychological.
Important as they are, elucidating the neurohormones released during stress and relating them to body systems is not even the whole story. If that were all there was to how stress works, you would expect any physical reaction to occur immediately, since these hormones typically remain elevated for only a short time. And you would expect everyone to show some physical reaction. Certainly, not all people suffer a heart attack or asthma attack when they get upset. Some seem able to take stress in their stride, while others routinely are hobbled.
Lawrence Brass, M.D., associate professor of neurology at Yale Medical School, found that severe stress is one of the most potent risk factors for stroke more so than high blood pressure—even 50 years after the initial trauma. Brass studied 556 veterans of World War II and found that the rate of stroke among those who had been prisoners of war was eight times higher than among those veterans who had not been captured.
The findings at first confused Brass. After all, the stress hormones that cause heart disease and stroke are elevated only for a few hours after a stressful event. "I began to realize we would have to take our understanding of stress farther when I began to see that in some people stress can cause disease years after the initial event," he says. He concluded that the immediate effect of the war trauma on the stress response system had to have been permanent. "The stress of being a POW was so severe it changed the way these folks responded to stress in the future—it sensitized them."
Their neurohormonal system was kicked off-kilter. Instead of churning out the normal amount of hormones in the face of stress, their systems were now so deregulated that at the slightest provocation, they either pumped out too much of some chemicals needed or not enough of others. "Years of this kind of hormonal assault may have weakened their cardiovascular systems and led to the strokes," Brass says.
Brass was unable to document actual changes in the neurohormonal system. But another study, of child abuse victims, reported at a meeting of the American Psychiatric Association, provides some of the earliest proof that stress can physically alter people. With magnetic resonance imaging, researchers took pictures of the brains of 38 women, 20 with a documented history of sexual abuse, 18 without. Among those women sexually abused as children, the researchers discovered, the hippocampus is actually smaller than normal. A tiny seahorse-shaped structure in the middle of the brain, the hippocampus is partially responsible for storing short-term memory. It is activated by some of the same neurohormones released during stress. "What we are seeing," says Murray Stein, Ph.D., of the University of California at San Diego, "is evidence that psychological stress can change the brain's makeup."
If stress sensitization begins with a major trauma and results in wholesale neurochemical and neuroanatomical changes, there should be other examples of its ravages. Perhaps, but they won't be easy to find, says UMass's King. "Most kids who suffer a trauma are not brought to the doctor," she says. "They get through the problem, go on with their lives, and wind up in our offices years later, suffering from depression or heart disease. And unless we were able measure amounts of hormones released before the initial exposure to stress, we wouldn't know if the levels were elevated." So researchers are looking at laboratory animals.
Even the lowly rat appears to become sensitized to stress. One study at UMass found that rats repeatedly stressed by exposure to a life-threatening cold and being deprived of maternal contact immediately after birth became hyper-responsive to stress. "Rats stressed from birth had a blunted release of ACTH in response to later stress," reports King. Then she reexposed them to cold after the age of 14 days, when their hypothalamic-pituitary axis matures. "Without enough ACTH, the rats were less able to mount a fight-or-flight response. The trauma of the early stress seems to have altered their response system."
"Hormonal changes from stress sensitization are quite clear in animals," notes Delaware's Levine. His own studies of monkeys document permanent changes in cortisol output in response to stress among monkeys subjected to early psychological trauma. "What's interesting are the fine variations in the changes depending on the type and time of the trauma," Levine says.
For instance, monkeys separated from their mothers for a mere 15 minutes a day during the first few months of life develop a stress response system that is slightly muted, compared with monkeys reared normally. But if the monkeys are separated from their mothers for a full three hours a day during the first few months, their later response to stress is hyperreactive. These sensitized monkeys literally run around the cage or cower in a corner in the presence of other nonthreatening animals.
"At first this may appear contradictory, but actually it is logical," Levine explains. "Being separated from their mothers for a few minutes a day is stressful, but not traumatic. It is not life-threatening, and so the animals did not have to develop a different set of mechanisms to get through that time. The muting of their stress response can be seen as a kind of defense against this daily intrusion," as if the monkeys are telling themselves "why get all worked up over this when I know it soon will be over."
"On the other hand, being separated from their mother for three hours a day is very traumatic," observes Levine. "Anything can happen during that time, so the monkeys must develop a heightened sense of awareness to protect themselves. This need may permanently alter their response so it is hyperresponsive all the time."
Is the same true for us? "We do know that sensitization happens, but we don't know what kind of stress it takes or when the stress must take place in order to produce the changes. There are a lot of variables in humans that are very difficult to control for, like the emotional environment in the home, genetic susceptibilities, and more. Some factors may cancel out the effects of an early trauma. We don't know."
The most likely truth about stress sensitization is that it is not a simple alteration in the amount of any single stress hormone. "It takes finely-tuned amounts of many neurohormones for the hypothalamic-pituitary axis to remain in balance," says Georgia Witkin, Ph.D., director of the Stress Program at Mt. Sinai Medical Center in New York. "No one thing is going to explain stress because there is not just one chemical reaction to stress. And it also does not mean that everyone who loses a parent or is the victim of a violent crime will suffer from stress the rest of his life. There are things about individuals—genetic susceptibilities, pre-existing medical conditions, the environment they were brought up in, any alteration that may have taken place in their HPA axis—that must all be factored in.
"But the first pieces of the puzzle are being put into place. Looking at stress as a chemical reaction and realizing that this reaction, if strong enough, can change how we react in the future, offers the possibility of explaining many things we have witnessed regarding stress. For instance, the reactions we see in rats that are exposed to early trauma may give us a biological perspective on the phenomenon of learned helplessness. Perhaps what we call learned helplessness is biologically-programmed helplessness. If these animals become physically unable to respond to stress because trauma has altered their biology, we can't really call that learned behavior."
If this new picture of stress is not yet quite in full focus, that's because it requires the melding of disciplines ranging from genetics to psychology to medicine, and demands a new theory of mind/body interactions. But it holds the promise of entirely new strategies to combat stress.
Roosevelt's Smith envisions the day when "we may be able to develop drugs that can retune the entire neurochemical system. I think it's going to take years more research to better understand how an early trauma actually alters the neurochemical system. What is the mechanism by which psychological stress changes the way the brain communicates with the body? Does the same stress cause the same changes all the time? When are the developmental periods during which stress may be most harmful? As we continue to unveil the complex interactions between the mind and body, we may be able to isolate these reactions. That raises the possibility we can develop drugs to change them."
For now, says UMass's Jean King, "we have to remember that the reason some people deal poorly with current events is because of a past trauma. We must remember that there are physical reactions in our bodies when we are under stress and the extent to which we endure these reactions may be dictated by our past. Telling someone to 'just take it easy' is of no help. We are still a long way from knowing just what to say, but we are getting there.
The future may hold specific ways of desensitizing brain and body so that they do not automatically hyperrespond to minor provocations. But for now, recognition of stress sensitization requires one all-important change in the way most of us approach de-stressing.
"If you wait until you're feeling stressed before you employ some technique for managing stress," contends psychologist Robert Epstein, Ph.D., "it's already too late. You need to have a bag of tricks that you can deploy proactively. If you turn to them throughout the day, that changes your threshold of stress tolerance."
Epstein, director emeritus of the Cambridge Center for Behavioral Studies and a researcher at San Diego State University, insists that "it's more important than ever to learn as many antistress techniques as possible, as young as possible."
"What we can now get out of the notion of sensitization is that people being treated for stress need individualized therapies," adds Saki F. Santorelli, Ed.D., associate director of the Stress Reduction Clinic at the University of Massachusetts Medical Center. "If we are saying that everyone responds to stress differently because of past experiences, then as therapists we need to be flexible and allow each person to focus on the part of therapy that works best for them. The only way to find that out is by trying different stress-reduction techniques."
There is no one-size-fits-all way to reduce stress. For example, "study upon study has shown that simple relaxation does not work in many people," says Rachel Yehuda, Ph.D., of Mt. Sinai Medical Center in New York. "Telling someone who has been sensitized to stress to just relax is like telling an insomniac to just fall asleep."
"What you don't want to do is resort to quick fixes that have no staying power," says Santorelli. "Smoking cigarettes, drinking alcohol, binging on food; these are sure-fire stress failures. They may give the impression that they are relieving tension, but they will not work over time and sooner or later you will be right back where you started." He also advises those who feel stressed to avoid coffee and high-fat foods. "Caffeine is a stimulant and foods high in fat make the body work overtime to digest them, so both will probably add to your level of stress."
At Santorelli's clinic, patients are taught mindfulness meditation, which comes out of the Buddhist tradition. Practitioners set aside 20 to 40 minutes a day when they focus on calming and becoming aware of their bodies with the aim of catching them—and interrupting them—in the act of hyperresponding to stress. "But the meditation really becomes a way of life. Once you begin practicing you realize that whenever you start feeling stressed during the day you are able to retrieve the feelings of relaxation you get during deep meditation. It becomes a way to take a few breaths and settle down just when you feel like you are beginning to explode."
Other forms of meditation use other devices to bring on moments of quiet contemplation, but all are designed to get you to focus on your body. "The most important thing is becoming aware of your body so you can sense when you are getting stressed. Meditation is an excellent way to do that" says Santorelli. "But it's not for everyone."
If meditation is not for you, maybe biofeedback is. There are three main forms of it: electromyography (EMG), galvanic skin response (GSR), and electroencephalography (EEG). By attaching electrodes to a body system that readily reacts to stress—muscles, skin, and brain waves, respectively—you can monitor your actual stress level and learn to control, even reduce it. Modern biofeedback devices give off some signal a blinking light, a bell—that announces a high level of tension. You concentrate on slowing the blinking light or bell.
Studies have found that each form of biofeedback works best for specific stress-related problems. EMG biofeedback, for example, reduces tension headaches; it allows people to focus and relax the muscles in the forehead that cause head pain. GSR seems to work best for stress-induced migraines, which tend to coincide with a rise in body temperature. EEG biofeedback leads to the deepest relaxation states.
What Calms You
But you don't have to meditate or go to a biofeedback clinic to avoid stress. "I meditate regularly, but when I am feeling unusually stressed I practice yoga or go exercise or tend to my garden or I hang out with family or even just read and write," Santorelli says. "You have to become aware of what calms you best."
For Jean King, Ph.D., of the UMass Medical School, listening to music, going for a walk, or exercising always seems to put her mind at ease. "I love the water, so if I'm having a rough day I just go and look at it. I don't even have to go in, all have to do is be near it."
Boston University biologist Eric Widmaier, Ph.D., confides that he used to combat stress by running and exercising. "But I've changed to a more thoughtful approach." He is an advocate of "internal conversations" in which he asks himself, "am I doing the right thing?" But the most important technique, he says, is "to learn to say no. People are constantly pushing at us by asking for favors."
One of the best-studied stress-relievers is the relaxation response, first described by Harvard's Herbert Benson, M.D. Its great advantage is that it requires no special posture or place. Say you're stuck in traffic when you're expected at a meeting. Or you're having trouble falling asleep because your mind keeps replaying some awkward situation.
Although you can turn to this exercise any time you feel stressed, doing it regularly for 10 to 20 minutes at least once a day can put you in a generally calm mode that can see you through otherwise stressful situations.
Epstein, who has searched the world literature for techniques people have claimed valuable for coping, focuses on those that are simple and powerful. He calls them "gems," devices that work through differing means, can be learned in minutes, can be done anytime, anywhere, and have a pronounced physiological effect. At the top of his list is the quickest of all—a cleansing breath.
Take a huge breath in. Hold it for three to four seconds. Then let it out v-e-r-y s-l-o-w-l-y. As you blow out, blow out all the tension in your body.
"The research literature demonstrates that sitting in certain positions, all by itself, has a pronounced effect," says Epstein. Sit anywhere. Relax your shoulders so that they are comfortably rounded. Allow your arms to drop by your sides. Rest your hands, palm side up, on top of your thighs. With your knees comfortably bent, extend your legs and allow your feet, supported on the heels, to fall gently outward. Let your jaw drop. Close your eyes and breathe deeply for a minute or two.
It's possible to relax muscles without effort; gravity can do it all. Start with your neck and let your head fall forward to the right. Breathe in and out normally. With every breath out, allow your head to fall more. Do the same for shoulders, arms, back.
Find a comfortable posture and close your eyes. Imagine the most relaxed place you've ever been. We all have a place like this and can call it to mind anywhere, any time. For everyone it is different. It may be a lake. It may be a mountain. It may be a cottage at the beach. Are you there?
Five—Count 'Em, Five—Tricks
Since you can never have too many tricks in your little bag, here are some "proven stress-busters" from Paul Rosch, M.D., president of the American Institute of Stress:
"Beating stress is a matter of removing yourself from the situation and taking a few breaths," says Rosch. "If I find myself getting stressed I ask myself 'is this going to matter to me in five years?' Usually the answer is no. If so, why get worked up over it?"
The Power of Understanding
Simply knowing about stress sensitization seems to help some. "We tell patients about stress sensitization and I see a change in them," Yehuda says. "We explain that they have inappropriate reactions to stress because something has gone wrong with control mechanisms in the brain. It is like a light goes on and they can see: 'Oh, so that may be the problem.' They do the same meditation and therapy but they are aware of the basis of their problem. There is something for them to focus on. There is a reason for them to say 'I'm not crazy. This is something real.'"
Quick, which would you rather be: late to work or lunch for a lion? The stress response we have today is out of sync with current needs. But it once was a Jurassic perk.
Nowadays, we are bombarded with what might be called the mythology of stress, which suggests that our psychological and physiological well-being is constantly threatened by degrees of stress unparalleled in history. Nothing could be farther from the truth.
What are some of these real or perceived stressors with which we continually do battle? Coping with rush-hour traffic, job and financial difficulties, troubled relationships, and family problems are just a few of hundreds of stressful stimuli that can be identified.
Anxiety over personal problems (will I be able to pay the rent this month?), or more global concerns (will there be another war?) is another type of stress that we all encounter much too often.
Nonetheless, anxiety and these other stressors are not immediate threats to survival, even if they do raise our blood pressure a bit now and then. Of greater concern is that the internal defense mechanisms of the body respond to these types of psychological stimuli in the same way as they would respond to life-threatening ones.
Why is this unfortunate? Because over the long haul, excess release of potent stress-fighting factors like the adrenal-gland hormones cortisol and epinephrine (also known as adrenaline) can suppress the immune system, cause ulcers, produce muscle atrophy, elevate blood sugar, place excessive demands on the heart, and eventually lead to the death of certain brain cells.
A person in the midst of a divorce does not require the hormonal, neuronal, and metabolic responses of someone who falls through thin ice on a wintry pond—yet in both cases the same internal changes are occurring.
Why do emotionally stressful events elicit the same chemical changes in our bodies as do events that are actual threats to survival? The answer may lie in a comparison of stress as we know it today and stress as it must have been when vertebrate animals were first evolving.
Are we really any more "stressed out" than our prehistoric ancestors? Presumably not, since the defense mechanisms that developed in mammals like ourselves did so very early in the evolution of life. We even see similar biological responses to stress in non-mammalian vertebrates like birds and reptiles.
These defenses consist of hormonal and neuronal signals that increase breathing, accelerate heart rate, increase blood pressure, increase the liver's ability to pump sugar into the bloodstream, and open up blood vessels in the large muscles to maximize the delivery of nutrients and oxygen.
The net effect is an animal that has lots of fuel in its blood, a more forceful heart to pump the blood around, plenty of oxygen, and efficient muscles. For an antelope in the wild that has spotted a nearby lion, these changes are exactly what the antelope needs to avoid becoming a meal.
Not surprisingly, then, animals evolved internal mechanisms to combat the stresses of infection, starvation, dehydration and pain, to name a few. Cortisol breaks down bone, muscle, fat, and other body tissues to provide material for the liver to convert into sugar. This sugar, essentially formed by the body's own self-digestion, can supply the needs of the heart and brain during a crisis. The natural pain-killer endorphin developed to combat severe pain.
Picture the antelope being attacked by the lion, but escaping to live another day. Its endorphin would allow the animal to cope with the pain of its wound, if only temporarily, and continue with the herd. Other hormones enable the kidney to retain more water than normal during periods of drought and dehydration.
All of these varied measures are short-term responses to very different types of stress, but they act in a concerted way to give an organism a fighting chance to get back on its feet.
Imagining the types of stress our paleolithic forebears must have encountered makes our daily aggravations seem much less overwhelming. Prior to the advent of agriculture, the typical cave-dweller would rarely have had the luxury of a steady and nutritious diet. On the contrary, malnutrition, vitamin and mineral deficiencies, even starvation would have been extremely common in the winter months, and sporadic dehydration from lack of clean or available water may have been common in the summer.
Hypothermia was a constant threat in the winter, especially in northern climes during the many ice ages. Injuries and infections that resulted from untreated minor wounds or parasite invasion would not only have been physiologically stressful but often lethal. Anthropological data suggest that our ancestors suffered many of the same maladies that continue to plague us today (arthritis, back problems, tooth decay, osteoporosis, to name a few).
However, as stressful as those conditions are for modern man, they would have been far more stressful at a time when no medical treatment of any kind was available.
What about the other type of stress that is not life-threatening, but is perceived to be of potential danger? When the antelope spotted the lion, there was not yet physical damage to the antelope's body. Nonetheless, the hormonal systems responded as if the damage was already done, in anticipation of impending doom. If the crisis were luckily averted, a complex system of hormonal feedback loops would apply a brake on the stress response to prevent unabated secretion of cortisol and other stress hormones.
Our prehistoric ancestors did not need to negotiate city traffic and deal with short-tempered bosses, but they had their share of psychological stress that produced no actual physical bodily insult.
Not knowing when (or if) your next meal will come would have been (and for much of the world's population continues to be) a chronic source of anxiety. Each empty-handed trip back to the cave would have increased the tribe's fears for the next day.
For that matter, obtaining a meal might have meant coping with the terror of chasing down a herd of animals much faster and larger than oneself, using a puny flint arrowhead tied to a stick.
Prehistoric man also differed in one profound way from modern man. Although an awareness of the cycles of nature and physical principles like gravity would likely have been present in even our most primitive ancestors, an understanding of the forces of nature would have completely eluded them.
Having no understanding of science meant having no sense of control over one's environment. Ancient man appears to have worried endlessly about celestial "beings" (sun gods, moon gods, etc.), and we know that until relatively recent times it was common for people to assign human traits to these deities.
This would have implied that it was within the realm of possibility for, say, the sun god to feel angry or neglected one day, thus deciding not to rise and plunging the world into darkness and chaos. Imagine going to sleep each night fretting that you may have failed to properly perform a certain worshipful ritual and that as a consequence your entire tribe or family might be forever doomed to darkness and misery.
From both a physical and a psychological vantage point, our ancestors lived a much more stressful existence than we do today. The mechanisms that evolved to combat the deleterious effects of those stressors are still intact and usually serve us well.
However, we clearly make things worse for ourselves. Take compulsive exercisers. These people can actually become addicted to strenuous exercise, because this behavior imposes a severe stress on metabolism and results in the steady release of endorphin. Responsible for "runner's high," this pain-killer is similar to morphine in its addictive capabilities.
Extreme exercise also releases cortisol, which though useful in maintaining circulatory and respiratory function, can lead to immunosuppression, bone loss, hypertension, and death of brain cells. In yet another scenario, meeting a deadline at work is a source of pressure, but is not life-threatening, and yet it contributes to ill health by invoking an unnecessary release of stress hormones.
Are we stressed in today's society? Of course we are. But the important thing to remember is that all animals, including ourselves, are confronted with innumerable types of stress and always have been. We should ignore the incessant mantra of ours being the Age of Stress and put things in a more historical and evolutionary perspective.
Given the choice, who wouldn't prefer the aggravation of two working parents getting their kids off to day care or school on time to the dread of being eaten in one's sleep by a lion?