November. 25 (HealthDay News) -- Negative changes in health behaviors are a major reason why heart patients with depression have an increased risk of cardiovascular events such as heart attack, say U.S. researchers who followed 1,017 outpatients with stable coronary heart disease for an average of 4.8 years.

Depression has long been recognized as a risk factor for cardiovascular disease in healthy people and for recurrent events in patients with cardiovascular disease. But the reason for this association hasn't been clear.

Dr. Mary A. Whooley, of the VA Medical Center in San Francisco, and her colleagues used a questionnaire to measure the heart disease patients' symptoms of depression. The researchers then used various models to evaluate the connection between subsequent cardiovascular events (such as heart failure, heart attack, stroke), depression, disease severity at the start of the study, and biological and behavioral factors.

The researchers found that patients with depression had a 50 percent greater risk of cardiovascular events -- 10 percent among those with depression compared to 6.7 among those without depression. When the researchers adjusted for other existing conditions and cardiac disease severity, depression was associated with a 31 percent increased risk of cardiovascular events.

Whooley and her colleagues further adjusted for certain health behaviors, including physical inactivity, and found there was no longer a significant association between depression and cardiovascular events. They calculated that physical inactivity was associated with a 44 percent greater rate of cardiovascular events.

Heart patients with depression are less likely to follow dietary, exercise and medication recommendations, and poor health behaviors can lead to cardiovascular events, said the authors of the study, which was published in the Nov. 26 issue of the Journal of the American Medical Association.

"Understanding how depression leads to cardiovascular events is necessary for developing interventions to decrease the excess cardiovascular morbidity (illness) and mortality (death) associated with depression," Whooley and her colleagues wrote.

They said their findings "raise the hypothesis that the increased risk of cardiovascular events associated with depression could potentially be preventable with behavior modifications, especially exercise. Given the relatively modest effects of traditional therapies on depressive symptoms in patients with heart disease, there is increasing urgency to identify interventions that not only reduce depressive symptoms, but also directly target the mechanisms by which depression leads to cardiovascular events."

SOURCE: Journal of the American Medical Association, news release, Nov. 25, 2008