The increased risk of cardiovascular events for patients with coronary heart disease and symptoms of depression appears to be largely explained by a change in health behaviors, especially a lack of physical activity, according to a study in the November 26 issue of JAMA.

Depression has long been recognized as a risk factor for the development of cardiovascular disease in healthy patients and for recurrent events in patients with established cardiovascular disease. Despite the substantial body of evidence demonstrating a strong link between depression and cardiovascular disease, the explanation for this association remains unclear, according to background information in the article. "Understanding how depression leads to cardiovascular events is necessary for developing interventions to decrease the excess cardiovascular morbidity and mortality associated with depression," the authors write.

Mary A. Whooley, M.D., of the VA Medical Center, San Francisco, and colleagues conducted a study to determine why depressive symptoms are associated with an increased risk of cardiovascular events. The study included 1,017 outpatients with stable coronary heart disease followed-up for an average of 4.8 years. Symptoms of depression were measured with a questionnaire, and various models were used to evaluate the extent to which the association of depressive symptoms with subsequent cardiovascular events (heart failure, myocardial infarction, stroke, transient ischemic attack or death) were explained by disease.

The researchers found that participants with depressive symptoms had a 50 percent greater risk of cardiovascular events: the age-adjusted annual rate of cardiovascular events was 10.0 percent among the 199 participants with depressive symptoms and 6.7 percent among the 818 participants without depressive symptoms. Adjustment for physical activity was associated with a reduction in the strength of association between depressive symptoms and cardiovascular events.

When adjusted for other existing conditions and cardiac disease severity, depressive symptoms remained associated with a 31 percent higher rate of cardiovascular events. After further adjustment for certain health behaviors, including physical inactivity, there was no longer a significant association between depressive symptoms and cardiovascular events. Physical inactivity was associated with a 44 percent greater rate of cardiovascular events, after adjusting for various factors.

The researchers note that patients with depressive symptoms are less likely to adhere to dietary, exercise, and medication recommendations, and poor health behaviors can lead to cardiovascular events.

"These findings raise the hypothesis that the increased risk of cardiovascular events associated with depression could potentially be preventable with behavior modification, 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."