Stress :: How mental stress leads to physical ailments

Prolonged stress weakens the immune system, strains the heart, damages memory cells and deposit fats at the waist, says Dr. Bruce McEwen of the neuroendocrinology laboratory, Rockefeller University, and author of a new book, The End of Stress as We Know It.

Stress has been implicated in aging, depression, heart disease, rheumatoid arthritis, diabetes and other illnesses.

Researchers have known for decades that physical stress takes a toll on the body. But only recently have the profound effects of psychological stress on health been widely acknowledged. In the last decade researchers have convincingly demonstrated that psychological stress can increase vulnerability to disease – and have begun to understand how this occurs.

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

Central to all this is a novel conception of stress developed by McEwen. According to his model, it is not stress per se that is harmful. 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 and exercise; by the presence or absence of personal relationships; by income level and social status. In moderate amounts, the scientists argue, stress can be benign, even beneficial.

Preparing to, say, avoid a speeding car, the body puts physiological processes essential in mobilizing a response – the cardiovascular system, immune system, endocrine glands and brain regions involved in emotion and memory – into action. Nonessential functions like reproduction and digestion are put off. Stress hormones like adrenaline and cortisol flood the body. Heart rate and blood pressure rise, respiration quickens, oxygen flows to the muscles, and immune cells prepare.

This process of allostasis was developed, McEwen points out, for the dangers prehistoric humans faced like a lion or a shortage of meat. When stress persists for too long or becomes too severe, he says, 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.

Dr. Sheldon Cohen, psychologist at Carnegie Mellon University, found that 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. The longer the stress persisted, the greater the risk of illness.

Allostatic load is often made worse, 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.

Ways in which stress hurts you physically:

* Sustained stress and the resulting overproduction of cortisol has a chilling effect on the hippocampus, the brain part involved in memory formation. Cortisol, studies have shown, can shrink nerve cells in the hippocampus and halt the creation of new neurons there.

* A primary cortisol function is to help mobilize energy in times of acute stress by releasing glucose into the blood. But when cortisol remains chronically elevated, it sends fat into storage at the waist and increases heart risk.

* A Carnegie Mellon University team found strong evidence that stressed people are more likely to become infected with colds and influenza and had more severe symptoms after becoming ill.

* A direct link between stress and more serious diseases, however, has been more difficult to establish.

Recent studies have provided increased support for the notion that stress contributes to heart disease, and researchers have tied psychological stress, directly or indirectly, to diabetes, rheumatoid arthritis, fibromyalgia, severe depression and other mental disorders.

But the influence of chronic stress on other diseases like cancer remains controversial.

-The New York Times-

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