Stress and disease may be linked, but how strongly?

It’s become a popular notion that chronic stress can have a wide range of medical consequences, from raising your blood pressure to causing cancer. And this has prompted many Americans to attempt to “de-stress” by taking up such practices as meditation, running or yoga.

The potential hazards of chronic stress were highlighted again when California scientists reported two weeks ago that they had found the first direct link between emotional stress and cellular changes associated with premature aging.

But before you stress out about the ill effects of stress, here’s something you need to know: 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 Center in New York City. 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.

Other studies, however, have found a link between chronic stress and 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.

In the recent stress and aging study, researchers from UC San Francisco followed 58 women, ages 20 to 50. Thirty-nine of the women had been taking care of a chronically ill child for periods from one to 12 years. The rest were raising healthy children. All the women were healthy -- and that’s important to note. Despite the potentially worrisome cellular changes that researchers found, these changes were not yet linked to diseases, said Bruce McEwen, a neuroendocrinologist at Rockefeller University in New York. For that, a longer study would be needed.

Linking biological changes to an actual disease is always the crucial step, said Cassileth, noting that studies in Scandinavia of women whose children died of chronic illness showed these women had no greater incidence of cancer or serious illness or a higher death rate than others.

In the new study, it was clear that in women who were more stressed, as gauged by their subjective ratings of stress and by the duration of their caregiving, cells showed signs of premature aging. Their telomeres, tiny structures on the tips of chromosomes, were shriveling up faster than normal. Like the plastic 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 UC San Francisco 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, said Elizabeth Blackburn, a UC San Francisco professor of biochemistry and biophysics and a coauthor 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 with women in both groups who rated their stress lower, said Epel.

“It’s how you perceive stress that is important, not caregiving per se,” 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 may be difficult to do.

The California study is the latest in a series of findings suggesting 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 non-caregivers 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 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 high for the subjects’ ages -- in this case as high as those found in 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 and at work, financial stress and stress surrounding 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 works -- jogging, meditation, repetitive prayer, even zoning out watching tropical fish, said 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 Benson, “it gives the body a chance to reconstitute.”