In a study released three weeks ago, California scientists announced they had found the first direct link between emotional stress and cellular changes associated with premature aging.

The study, which was widely praised by other researchers, strengthens the popular belief that emotional stress may have serious medical consequences. It is also consistent with the idea that stress-reducing practices such as yoga, meditation, jogging, or any version of the “relaxation response” may reduce the risk of certain diseases. Before you stress out about the ill effects of stress, a few cautions. Many of the biochemical links between feeling stressed and getting sick are still unknown. And stress clearly doesn’t cause everything.

“For a long time, people believed that stress caused cancer. It’s not true,” said psychologist Barrie Cassileth, chief of the integrative medicine service at Memorial Sloan-Kettering Cancer Institute. Several studies have looked at people who have lost a child, been in concentration camps or psychiatric wards, or who were prisoners of war – and found no link between those stressful situations and cancer.

On the other hand, previous studies have shown that chronic stress is linked to a higher risk of heart attack, high blood pressure, and insomnia, said Dr. Herbert Benson, president of the Mind/Body Medical Institute and an associate professor of medicine at Harvard Medical School. Stress is also associated with more intense hot flashes, a lower threshold for pain, and increased anxiety, depression, excessive anger, and hostility.

That said, the new study is “a very important milestone” in mind body research, said Bruce McEwen, director of neuroendocrinology at Rockefeller University.

In a commentary accompanying the California paper in the Proceedings of the National Academy of Sciences, Robert Sapolsky of Stanford University wrote that the discovery is “remarkable” and “exciting” because it ties together an emotional state with very fundamental cell biology.

In the study, researchers from the University of California, San Francisco followed 58 women ages 20 to 50; 39 of the women were taking care of a chronically ill child and the rest were raising healthy children. The sick children had been diagnosed between one and 12 years ago. All the women were healthy.

But in women who were more stressed, as gauged both by their subjective ratings of stress and by the duration of their caregiving, their cells showed signs of premature aging. Their telomeres, tiny structures on the tips of chromosomes, were shriveling up faster than normal. Like the tips of shoelaces, telomeres protect the ends of chromosomes; once telomeres get too short, a cell can no longer divide.

The longer a woman took care of a sick child, the shorter were the telomeres in her white blood cells, said lead author Elissa Epel, a UCSF psychologist. The women who felt most stressed also had lower levels of telomerase, an enzyme that restores telomere length. And they had greater “oxidative stress,” a measure of damage done to cells by destructive forms of oxygen, noted Elizabeth Blackburn, a UCSF professor of biochemistry and biophysics and a co-author of the paper.

The women whose subjective ratings of stress were the highest had the equivalent of 10 years of extra aging in their immune cells, compared to women in both groups who rated their stress lower, said Dr. Epel.

“It’s how you perceive stress that is important, not caregiving per se,” Dr. Epel said, adding that the same external situation can produce different kinds of stress in different people. With “threat stress,” people feel that their very survival or self-esteem is in jeopardy, triggering feelings of anxiety and loss of control. Another person in the same situation might feel “challenge stress,” seeing the situation as an opportunity to rise to the occasion. One implication is that if you’re in what you perceive to be an unpleasantly stressful situation, change the situation if you can; if you can see the situation in a less stressful light, that may help, too, though this can be hard to do.

The California study is actually the latest in a series of findings documenting a link between chronic emotional stress and disease or immune system disruption.

In one 1999 study, University of Pittsburgh researchers found that people who were taking care of an ill spouse and experiencing stress had a 63% higher risk of death over a four-year period than noncaregivers in the same study.

At Ohio State University, the husband-and-wife team of Janice Kiecolt-Glaser, a psychologist, and Ronald Glaser, an immunologist, have found that spouses who take care of partners with dementia have weakened immune systems.

Small, experimentally produced wounds, for instance, take longer to heal in stressed caregivers, and immune responses to vaccinations are less vigorous. In a recent, six year study, the Glasers found that chronically stressed caretakers pump out excessive quantities of Il-6, an immune system chemical that is linked to heart disease, osteoporosis, arthritis, diabetes, and other conditions.

Like the California researchers, the Glasers found that Il-6 levels in the stressed caregivers were as high as those of people 15 years older, suggesting that stress may accelerate aging.

In terms of stress and heart disease, the most impressive study to date is a 52-country study published earlier this year in Lancet. Called INTERHEART, the study examined stress at home, at work, financial stress, and major life events in 24,767 people and found that stress raised heart attack risk 2.5 times, almost as much as smoking and diabetes.

Although previous studies had suggested a correlation between chronic stress and heart disease, this was the first time a large, cross-country study showed such a clear link, said Dr. Roger Blumenthal, director of preventive cardiology at Johns Hopkins Hospital.

The implication, he added, is that people “should work harder at decreasing stress, increasing exercise, and making time for hobbies. It’s ironic, but you have to make time to get away from stressors.”

How? Basically, by relaxing with whatever tricks work – jogging, meditation, repetitive prayer, even zoning out watching tropical fish, said Dr. Benson of Harvard. There are two keys to this: repetition, that is, repeating a sound, a word, a phrase, or even a movement, such as jogging or swimming. And when other thoughts pop into your mind, gently guide yourself back to your repetitive phrase or activity.

“The common denominator in all these things is that they break the train of everyday thought. If you can break that chain, even for just 20 minutes a day,” said Dr. Benson, “it gives the body a chance to reconstitute.”

Ms. Foreman is a lecturer on medicine at Harvard Medical School. Her columns are available at www.myhealthsense.com.