Interleukin 6 May Tie Depression to Heart Disease

Article excerpt

NEW YORK -- Interleukin 6 could be the hidden link between depression and cardiovascular disease, Gregory Miller, Ph.D., said at a symposium sponsored by the National Association for Research on Schizophrenia and Depression.

Currently, more than 30 studies show clear and significant associations between depression, MI, and cardiovascular mortality. Among them is the widely publicized research by Nancy Frazier Smith and her colleagues at McGill University, Montreal, which showed that high scores on the Beck Depression Inventory during the first week after MI correlated strongly with reduced 5-year survival.

Dr. Miller of the department of psychology at the University of British Columbia, Vancouver, said this rapidly expanding body of data raises questions about how depression exacerbates cardiovascular disease.

"How does a so-called 'brain' disorder, a nebulous psychological state like depression, get into the body to increase the risk of something so physical as a heart attack?"

In an attempt to answer this question, Dr. Miller has been studying the immune system and the inflammatory mediators involved in the pathophysiology of cardiovascular disease. "Coronary plaques form as a result of an inflammatory process, and we wondered whether depression somehow fosters this process."

He began by collecting blood samples from physically healthy, but clinically depressed, individuals in their 20s and 30s, and also from healthy, nondepressed, age-matched control subjects. There were no other psychiatric or medical differences between the two groups, and no histories of substance abuse or medication use in either cohort.

A study of the mean levels of various cytokines and immunomodulators between the two groups revealed two key findings: The level of interleukin 6 (IL-6), a key inflammatory cytokine, was 50% higher in the depressed individuals. The mean level of C-reactive protein (CRP), thought to be a very accurate predictor of MI risk, was 40% higher in the depressed individuals.

This latter finding is particularly troubling because the depressed subjects had a mean CRP level of 3.5 mg/L. According to the American Heart Association's current guidelines for cardiovascular risk assessment, any CRP level above 3 mg/L suggests high risk for cardiovascular disease. …