By Tara Parker-Pope
For years cardiologists and mental health experts have known that depression raises risk for heart attack by 50 percent or more.
But what hasn’t been clear is why depressed people have more heart problems. Does depression cause some biological change that increases risk? Does the inflammatory process that leads to heart disease also trigger depression?
The answer may be far simpler. A new study suggests that people who are depressed are simply less likely to exercise, a finding that explains their dramatically higher risk for heart problems.
Researchers, led by doctors from the Veterans Affairs Medical Center in San Francisco, recruited 1,017 participants with heart disease to track their health and lifestyle habits. As they expected, those patients who had symptoms of depression fared worse. About 10 percent of depressed heart patients had additional heart problems, during the study, compared with 6.7 percent of the other patients. After controlling for other illnesses and the severity of heart disease, the finding translates to a 31 percent higher risk of heart problems among the depressed people, according to the study published this week in the Journal of the American Medical Association.
But once the researchers factored in the effect of exercise, the difference in risk among depressed people disappeared. In the same study, patients who didn’t exercise, whether or not they were depressed, had a 44 percent higher risk of heart problems, after controlling for a variety of factors including medication adherence, smoking and other illnesses.
The findings are important because some earlier studies have suggested a link between antidepressant use and lower heart risk. The explanation may be that patients who take antidepressants start to feel better and take care of themselves, adopting healthy behaviors including exercise. In a study of nearly 2,500 heart-attack patients, published in the Journal of the American Medical Association in June 2003, behavioral therapy to treat depression didn’t change survival rates compared with patients who received regular care. But among about 20 percent of patients in the study who ended up on antidepressants, the risk of dying or suffering a second nonfatal heart attack was 42 percent lower. Another study, called Sadheart (which stands for Sertraline Antidepressant Heart Attack Randomized Trial) showed the death rate from heart-related problems was 20 percent lower among patients taking the drug, although the data weren’t statistically significant.
The research suggests that doctors treating patients for depression should also talk to them about their lifestyle habits, and encourage them to exercise. The findings, say the researchers, suggest that the heart problems associated with depression “could potentially be preventable.”
The evidence that health behaviors fully explain the link between depression and heart disease in this study is convincing, says Dr. Mary A. Whooley, professor of medicine, epidemiology and biostatistics at the University of California, San Francisco. However, she notes the study is limited to older men with stable coronary disease, and as a result, more study is needed of women and other patients with heart disease.
It remains an open question whether the study findings will change the way doctors counsel their patients. “The clinical practice question is a challenging one,” says Dr. Whooley. “It’s easy for us to tell patients to exercise, take their medicines, and refrain from smoking, but actually changing health behaviors is very difficult.”
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