The Heavy Cost of Chronic Stress

December 17, 2002
By ERICA GOODE
New York Times

Introduction

In this season of bickering relatives and whining children, of overcrowded department stores and unwritten Christmas cards, it is instructive to consider the plight of the Pacific salmon.

As the fish leap, flop and struggle upstream to spawn, their levels of cortisol, a potent stress hormone, surge, providing energy to fight the current. But the hormone also leads the salmon to stop eating. Their digestive tracts wither away. Their immune systems break down. And after
laying their eggs, they die of exhaustion and infection, their bodies worn out by the journey.

Salmon cannot help being stressed out. They are programmed to die, their systems propelled into overdrive by evolutionary design.

Humans, on the other hand, are usually subject to stresses of their own making, the chronic, primarily psychological, pressures of modern life. Yet they also suffer consequences when the body's biological mechanisms for handling stress go awry.

Prolonged or severe stress has been shown to weaken the immune system, strain the heart, damage memory cells in the brain and deposit fat at the waist rather than the hips and buttocks (a risk factor for heart disease, cancer and other illnesses), said Dr. Bruce S. McEwen, director of the neuroendocrinology laboratory at the Rockefeller University and the author of a new book, "The End of Stress as We Know It." Stress has been implicated in aging, depression, heart disease, rheumatoid arthritis and diabetes, among other illnesses.

Researchers have known for many decades that physical stress takes a toll on the body. But only relatively recently have the profound effects of psychological stress on health been widely acknowledged. Two decades ago, many basic scientists scoffed at the notion that mental state could affect illness. The link between mind and body was considered murky territory, best left to psychiatrists. But in the last decade, researchers have convincingly demonstrated that psychological stress can increase vulnerability to disease and have begun to understand how
that might occur.

"If you would have said to me back in 1982 that stress could modulate how the immune system worked, I would have said, `Forget about it,' " said Dr. Ronald Glaser, an immunologist at Ohio State University.

The more researchers have learned, the clearer it has become that stress may be a thread tying together many illnesses that were previously thought to be unrelated.

"What used to be thought of as pathways that led pretty explicitly to one particular disease outcome can now be seen as leading to a whole lot of different outcomes," said Dr. Robert M. Sapolsky, a professor of neurology at Stanford.

Central to this new understanding is a novel conception of stress, developed by Dr. McEwen, who has been studying the subject for more than three decades. According to his model, it is not stress per se that is harmful. Rather, the problems associated with stress result from a complicated interaction between the demands of the outside world and the body's capacity to manage potential threats.

That capacity can be influenced by heredity and childhood experience; by diet, exercise and sleep patterns; by the presence or absence of close personal relationships; by income level and social status; and by the piling on of normal stresses to the point that they overload the system.

In moderate amounts, the scientists argue, stress can be benign, even beneficial, and most people are equipped to deal with it.

Preparing to give a speech, take a test or avoid a speeding car, the body undergoes an elaborate series of adjustments. Physiological processes essential in mobilizing a response - the cardiovascular system, the immune system, the endocrine glands and brain regions involved in emotion and memory - are recruited into action. Nonessential functions like reproduction and digestion are put off till later.

Adrenaline, and later cortisol, both stress hormones secreted by the adrenal glands, flood the body. Heart rate and blood pressure rise, respiration quickens, oxygen flows to the muscles, and immune cells prepare to rush to the site of an injury.

When the speech is delivered, the test taken or the car avoided, another complex set of adjustments calms things down, returning the body to normal.

This process of "equilibrium through change" is called allostasis, and it is essential for survival. But it was developed, Dr. McEwen and Dr. Sapolsky point out, for the dangers humans might have encountered in a typical day on the savannah, the sudden appearance of a lion, for example, or a temporary shortage of antelope meat.

Blaring car alarms, controlling bosses, two-career marriages, six-mile traffic jams and rude salesclerks were simply not part of the plan.

When stress persists for too long or becomes too severe, Dr. McEwen said, the normally protective mechanisms become overburdened, a condition that he refers to as allostatic load. The finely tuned feedback system is disrupted, and over time it runs amok, causing damage.

Work that Dr. McEwen and his colleagues have conducted with rats nicely illustrates this wear-and-tear effect. In the studies, the rats were placed in a small compartment, their movement restricted for six hours a day during their normal resting time. The first time the rats were restrained, Dr. McEwen said, their cortisol levels rose as their stress response moved into full gear. But after that, their cortisol production switched off earlier each day as they became accustomed to the restraint.

That might have been the end of the story. But the researchers also found that at 21 days, the rats began to show the effects of chronic stress. They grew anxious and aggressive. Their immune systems became slower to fight off invaders. Nerve cells in the hippocampus, a brain region involved in memory, atrophied. The production of new hippocampal neurons stopped.

Dr. Sheldon Cohen, a professor of psychology at Carnegie Mellon University, has found that people respond much the same way. Among volunteers inoculated with a cold virus, those who reported life stresses that continued for more than one month like unemployment or family problems were more likely to develop colds than those who reported stress lasting less than a month. The longer the stress persisted, the greater the risk of illness.

Allostatic load is often made worse, Dr. McEwen said, by how people respond to stress, eating fatty foods, staying late at work, avoiding the treadmill or drinking to excess. "The fact is that we're now living in a world where our systems are not allowed a chance to rest, to go back to
base line," he said. "They're being driven by excess calories, by inadequate sleep, by lack of exercise, by smoking, by isolation or frenzied competition."