PITTSBURGH, Oct. 22 -- Previous studies have suggested that homocysteine, a by-product of dairy and meat foods, is a risk factor for heart disease. But now, evidence from a new study by University of Pittsburgh researchers counters this premise. Their work is published in the current issue of the American Heart Association's (AHA) journal, Arteriosclerosis Thrombosis and Vascular Biology.
Results from the Multiple Risk Factor Intervention Trial (MRFIT) suggest that homocysteine more likely indicates the extent of atherosclerosis or inflammation rather than promotes the processes that lead to the end points of heart disease, such as stroke or heart attack.
Pitt researchers analyzed blood samples and found no difference in homocysteine levels between men who suffered heart attacks and men who had not experienced heart attacks.
"This indicates that the role of homocysteine in heart disease might be different than previously thought," noted Rhobert W. Evans, Ph.D., assistant professor of epidemiology at Pitt's Graduate School of Public Health. "Our study clearly challenges scientists and clinicians to re-evaluate the association between homocysteine and cardiovascular disease."
Most studies that have reported a link between homocysteine and heart disease are case-control studies. That is, the researchers have recruited two groups of individuals, the control group in which no one has suffered heart disease and the case group in which every individual has heart disease. The investigators then looked at medical histories of the patients and measured homocysteine levels at the same time.
"It is possible that the associations found in these retrospective case-control studies can be attributed to elevations in homocysteine concentrations that follow a heart attack or stroke," commented Dr. Evans.
Other studies have shown that homocysteine levels may increase after a heart attack or stroke. Pitt researchers also point out that homocysteine levels have been linked with other risk factors for heart disease, which may confound the association between homocysteine and heart disease.
The MRFIT study enrolled 12,866 men between 1973 and 1976 who were healthy with no reported cases of heart disease. In this prospective study, blood samples were taken and stored and the men were monitored for up to 17 years for heart disease.
"Our study is one of a few prospective studies that has examined the relationship between homocysteine levels and heart disease risk. We have found no causal link between homocysteine levels and heart disease," stated Dr. Evans.
Dr. Evans and his colleagues discount the possibility that the homocysteine in the stored blood samples degrades after storage. They also point out that dietary fluctuations do not explain the difference between their study findings and previous results by other investigators, because the men enrolled in the MRFIT study fasted before blood was drawn.
An editorial published in the AHA journal, Circulation, by David Wilcken, M.D., of the Prince Henry Hospital, Sydney, pointed to the fact that a review of the role of homocysteine and heart disease needs to be conducted.
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