Investigators have been looking for decades at psychological factors that might increase the risk of heart disease, explains author Reiner Rugulies, Ph.D., MPH, Dipl-Psych, from the University of California, San Francisco. The results -- including numerous findings on personality type and risk of heart disease -- have been largely inconsistent.

However, he concludes, research on depression and heart disease provides a far more consistent picture, indicating that "depression is associated with the development of [heart disease] in initially healthy people." In the review article, he examined 11 large-scale studies on depression and future heart disease published between 1993 and 2000. In each study, investigators categorized each participant as depressed or not depressed, then followed the participants for anywhere from 3 to 37 years to document myocardial infarction rate and cardiac mortality rate. The researchers assessed and tracked more than 36,000 men and women overall, most of them Americans.

Rugulies reports that "Depression was associated with a significantly increased risk of [heart disease] in 7 of the 11 studies" despite the subjects' initial good health. The depressed individuals were between 1.5 times and 4 times more likely than non-depressed counterparts to develop heart disease. The remaining 4 studies, Rugulies notes, also support a depression-heart disease link, but with weaker evidence.

The most striking association appeared in studies in which subjects were required to be diagnosed with clinical depression, not merely depressed mood, in order to be counted as "depressed." On the average, subjects with clinical depression were almost 2 times as likely as individuals with depressed mood and almost 3 times as likely as non-depressed individuals to develop heart disease.

Rugulies' conclusion that depression may be a risk factor for heart disease is in line with other recent reviews that have merely summarized the available research, but his conclusion is strengthened by a large-scale analysis of the reported data.

It stands in contrast to the conclusion of an earlier meta-analysis, published in 1988, whose author reported that the available research did not indicate a strong association between depression and future heart disease. However, at that time only three studies were in print that examined the long-term impacts of depression on heart status in otherwise healthy individuals. "The situation has changed substantially during the last 10 years; there are now many [such] studies," Rugulies explains.

Future research will look for the reason why depression precedes development of heart disease. For the present, knowledge of the link between depression and cardiac risk gives mental health clinicians another tool to evaluate their patients' health risks and overall health care plan.