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ATLANTA -- Serious depression can cause feelings of heartbreaking sadness. Depression can also, literally, contribute to a damaged heart. In fact, a host of studies have shown that depression is linked to a higher incidence of cardiovascular events and mortality in patients with cardiac disease as well as to a higher incidence of both fatal and nonfatal cardiovascular events in individuals initially free of coronary heart disease (CHD).
But what mechanism explains the relationship between depression and CHD risk? According to a new study by a team of Emory and Yale researchers published today in the May/June issue of the Journal of Psychosomatic Medicine, depression could threaten heart health by causing or promoting inflammation.
"We now know that atherosclerosis is an inflammatory process. Our study, which is the first of its kind to look at a wide population of younger, healthy adults, investigated the association between a history of a major depressive episode and the presence of low-grade systemic inflammation as measured by serum C-reactive protein (CRP) which is a marker of systemic inflammation and a strong risk factor for atherosclerotic heart disease," says Viola Vaccarino, MD, PhD, of the Emory Department of Medicine's Division of Cardiology, who headed the Emory/Yale research team.
The Emory scientists analyzed data from the Third National Health and Nutrition Examination Survey, a representative sample of the US population from 1988 to l994. Participants included a total of 6,149 people between the ages of 17 to 39 years who were free of cardiovascular diseases and chronic inflammatory conditions (such as rheumatoid arthritis, chronic bronchitis, asthma and emphysema). The Diagnostic Interview Schedule (DIS) developed by the National Institute of Mental Health was used to screen the research subjects for major depressive episodes.
The Emory and Yale researchers found that men with a history of a major depressive episode had 2.77 times higher odds of elevated CRP compared with never depressed men. The elevated levels of CRP in this study are indicative of a subtle and persistent increase in systemic inflammation, a response linked to cardiovascular risk.
"We found that a recent history of a major depressive episode was strongly associated with elevated CRP in men between the ages of 17 and 39," says Dr. Vaccarino. "The graded association with timing of depression -- the more recent the last depressive episode, the higher the probability of elevated CRP -- is our most important finding. This casts validity to the hypothesis that depression and CRP may be truly linked. "
However, the researchers did not find a similar strong connection linking depression with elevated CRP in women. "That is a surprising finding, " says Dr. Vaccarino. "However, we know that women in the absence of depression are twice more likely than men to have elevated CRP, which is in itself an intriguing finding. One possibility is that in these younger, pre-menopausal women, estrogen already has a pro-inflammatory effect and depression adds little to this."
The researchers hypothesize that depression might promote an inflammatory response in men by activating the immune response. Another possibility is that the effects of depression on inflammation might be due to psychological stress, which has been shown to increase oxidative state and could initiate an inflammatory response in artery walls.
"It may also be that depression leads to higher CRP levels through some indirect, non-biological mechanism involving a health behavior," Dr. Vaccarino explains. "For example, men who are depressed might smoke more and that would lead to higher CRP levels. However, our finding in men was adjusted for smoking, so it seems unlikely that smoking could explain the association we observed. But that does not mean there is not another, still unrecognized intervening factor."