Stress has been linked to many physical ills, but scientists are just beginning to understand how it acts on the body.
On Jan. 17, 1994, the day a major earthquake rocked Los Angeles, the number of fatal heart attacks recorded in the region was five times the expected number-24 compared with a daily average of 4.6 for the preceding week. The heart attack rate also soared when Iraqi missiles hit Israeli cities during the Persian Gulf War of 1991. The first day that missiles struck, deaths from heart attacks and strokes in Israel rose to 147, from the usual average of 92.9.
These dramatic events underscored the threat that severe stress poses to the heart. But events need not be so dramatic to endanger the heart. Robert Eliot, a cardiologist who heads the Institute of Stress Medicine in Scottsdale, Arizona, estimates that stress-related heart conditions claim the lives of as many as half a million Americans each year.
Nor are heart attacks the only physical damage to the body inflicted by stress. Researchers in various fields have linked stress to a suppressed immune system and other physical ills, including hypertension (high blood pressure), migraine headaches, sleep disorders, eating problems, asthma, and allergies. And physicians report that stress-based complaints such as fatigue, headache, and insomnia account for a large number of office visits. But scientists are just beginning to understand how stress affects the body.
Chemical messengers of stress
What we call stress is actually the body’s response to demanding situations or events known as stressors. Stressors can be external-an earthquake, for example-or internal, such as anxiety over an upcoming exam. Stressors can also be positive events, such as marriage, or a promotion at work. In response to stressors, the eyes, ears, skin, and other sense organs send signals to a part of the brain called the hypothalamus. On the basis of these signals and of past experience with stressors, the hypothalamus activates the stress response. It signals the nearby pituitary gland, which releases a hormone (chemical messenger) called adrenocorticotropin-releasing hormone (ACTH).
ACTH makes its way through the bloodstream to the adrenal glands, which sit atop the kidneys and release a number of hormones critical to the stress response. These include glucocorticoids, which supply the body with instant energy and suppress the immune response, and epinephrine (also called adrenaline) and norepinephrine (also called noradrenaline), which step up heart rate and blood pressure. This sequence is referred to as the hypothalamic,pituitary, adrenal axis, and the hormones the adrenal glands release are known collectively as stress hormones.
The stress hormones bring about changes throughout the body, not only elevating heart rate and blood pressure and providing energy, but also speeding up breathing, reducing hunger, stimulating thirst, and even widening the pupils of the eye to enhance vision. Through the body’s feedback system, we experience these physical changes as tension, fear, excitement, and other emotions.
This stress response is useful for reacting to an urgent, life-threatening situation, but when prolonged it can harm the body. In the short term, blood flow increases to the parts of the body that require energy, such as the arms and legs, thus improving the body’s ability to respond by “fight or flight.” Systems not needed in the emergency, such as the digestive system, are put on hold by directing blood flow away from them. But when the stress response remains activated for an extended period, the redirection of blood flow may lead to hypertension, digestive system upsets, and other health problems.
Stress and the heart
Because heart disease is such a major health risk, much early research on stress-related illness concentrated on the heart. The so-called Type A personality-aggressive, controlling, driven-quickly became associated with an increased risk for heart disease. Although this association was accepted for many years, long-term studies eventually determined that most Type A traits were unrelated to heart disease. However, one personality trait did appear to be consistently associated with heart disease: anger and general hostility.
This effect of stress on the cardiovascular system (heart and blood vessels) can crop up years after the initial exposure to a stressor. A recent study of 556 World War II veterans, conducted at Yale University, found that the rate of stroke among men who had been prisoners of war was eight times higher than that of men who had not been captured. (Stroke occurs when a rupture or blockage of a blood vessel causes injury to the brain.) The researcher who conducted the study concluded that the impact of severe stress on the body may be long-lasting, raising the body’s sensitivity to future stressors.
Animal studies support the theory that stress early in life can have lasting consequences. In a study of monkeys, young monkeys separated from their mothers for 15 minutes a day showed only a slight change in their stress response. But monkeys separated from their mothers for three hours a day during the first months of life had a greatly heightened stress response thereafter. Once sensitized to stress, they were likely to race around their cage or cower in a corner when exposed to even a mild stressor.
The health risks of stress
Chronic stress can also set in motion a slow but prolonged attack on the cardiovascular system by elevating blood pressure. The role stress plays in hypertension and the extent of its effect are still being investigated. But studies have found that the strain of a high-pressure job can lead to a chronic elevation of blood pressure, condition that increases the risk of heart disease. Studies have repeatedly shown that people working at high-strain jobs over which they have little control, such as waitresses, assembly-line workers, and people in middle-management positions, are at greater risk for hypertension.
Researchers at Duke University in Durham, North Carolina, reported in June 1996 that the amount of stress people are experiencing may provide a more accurate indication of heart disease risk than the standard physical test of heart function, running on a treadmill while heart rate is monitored. The researchers administered mental stress testing, such as complex math problems that had to be solved in a limited amount of time, to 126 people. They used sophisticated imaging techniques to detect changes in blood flow to the heart while the participants underwent testing. During a five-year follow-up, the investigators found that 27 percent of the people who responded poorly to the testing, as indicated by a greater reduction in blood flow, had suffered a heart attack, were experiencing angina (chest pain), or had severely clogged coronary arteries. By contrast, only 12 percent of the participants who did not have trouble with the tests had experienced serious heart problems.
While the role of stress in cardiovascular disease has been studied for decades, recent study of chronic stress’s impact on health has focused on its relationship with the immune system. The workings of the immune system are extremely complex and the ways in which stress interacts with this system are exceedingly difficult to unravel.
But scientists are beginning to identify these links. Although it had been demonstrated that injury to certain parts of the brain altered the immune response, the prevailing view among scientists had long been that the brain did not communicate with the immune system and that psychological factors such as stress did not influence immunity. Recent discoveries, however, have brought that view into question.
Stress and the immune system
In the 1980’s, scientists at Ohio State University measured the ways that anxiety reduces the body’s ability to produce interferon, a protein that is crucial to fighting disease. The researchers found that during college examination weeks, students had less interferon in their bodies and were far more likely to contract colds or the flu than at other times of the year.
This finding mirrors results obtained by researchers at Carnegie Mellon University in Pittsburgh. Study participants first answered a questionnaire aimed at determining their levels of stress. They then received nose drops containing cold viruses. Participants with high scores on the stress scale had a 90-percent chance of catching cold, compared with a 74-percent chance among participants with lower scores. The researchers found that stress boosted levels of a hormone called cortisol, which has been shown to suppress the immune system.
Studies conducted at Ohio State University in the 1990’s have shown that hostile feelings may disturb the immune response. The investigators asked 90 newlywed couples to resolve difficult issues, such as feelings about their mothers-in-law. While the couples tried to iron out their differences, instruments to which they were connected drew small blood samples at regular intervals. The blood was tested for levels of stress hormones. The researchers found that when couples became more hostile, blood levels of hormones that boosted immune response fell and levels of hormones that weakened the response rose.
Stress and arthritis
Other scientists have explored the role that stress might play in autoimmune disorders-diseases that result from an attack by the immune system on the body’s own tissues. What causes the immune system to tag a body tissue as foreign and mount an attack remains a mystery, but some findings implicate stress as a factor.
One of the most common autoimmune diseases is rheumatoid arthritis, a disorder that involves swelling, pain, and tenderness in the joints. Some people with this disease report that stress makes their arthritis worse. Researchers at Arizona State University studied 100 rheumatoid arthritis patients and found that those who said they were experiencing high levels of stress in their relationships with other people had twice the level of the hormone prolactin in their blood as those who did not report such stress. Other studies have shown that prolactin travels to the joints, where it sets in motion a series of reactions that results in swollen joints.
There is also good reason to suspect a role for stress hormones in disturbances of the large intestine-spastic colon, for example, which may produce chronic diarrhea, constipation, and cramping. Some cases of colitis-chronic inflammation of the colon-are also suspected of resulting from sustained stress, where no other clear cause can be found.
Can emotional strain cause illness?
As researchers work to link stress with disorders of specific organs and systems, some more general vulnerabilities to stress have become clear. For example, studies have established that people who are widowed are at risk of dying within a year or so of their spouse. Anniversaries-of deaths, for example-and major events, such as a wedding or the loss of a job, also arouse emotions strong enough to constitute stressors.
Research reported in 1995 suggested that stress levels can alter the immune response in patients with AIDS, especially when major stressors such as the death of a loved one occur. An ongoing study, conducted by researchers at the University of Florida and the University of North Carolina, followed 93 HIV-infected men for 6 months to 31/2 years. The more stressors the men encountered, the study found, the more likely that their condition worsened. Other research has found that cynical, hostile HIV-infected men had poorer immune function than those with a more positive attitude.
Chronic stress takes a toll on the body. Where it strikes and how we respond depends to a great extent on genetic predisposition, our past experience with stress, and other physiological factors not yet discovered. As a growing number of scientists examine the effects of stress on health, a new field known as psychoneuroimmunology has emerged. This discipline investigates the complex interactions of the nervous system, immune system, and hormonal system and the effects that human behavior-including stress-has on these systems and on health. Future findings may help us to avoid many illnesses caused by stress.