July 20, 2004 DALLAS, July 20 – Eating broiled or baked fish – but not fried fish or fish sandwiches – appears to lower the incidence of the most common irregular heartbeat among the elderly, according to a study published in today's rapid access issue of Circulation: Journal of the American Heart Association.
The study is the first to examine whether fish intake affects atrial fibrillation (AF). It's also the first to focus on the kind of fish meals eaten, said Dariush Mozaffarian, M.D., M.P.H., the study's lead author. "The results suggest that regular intake of tuna or other broiled or baked fish may be a simple and important deterrent to AF among older men and women," said Mozaffarian, instructor of medicine and researcher in the Channing Laboratory, Brigham and Women's Hospital and Harvard Medical School in Boston.
AF affects more than 2 million Americans. A chronic condition that causes disability through fatigue, shortness of breath and reduced exercise tolerance, it occurs when the heart's two upper chambers (the atria) quiver instead of beating effectively. Blood isn't pumped completely out of the chambers, so it may pool and clot.
If a blood clot leaves the heart and becomes lodged in an artery in the brain, a stroke results. About 15 to 20 percent of strokes occur in people with atrial fibrillation. The incidence of AF increases with age, rising to approximately 2 percent per year after age 65. Researchers analyzed data from the National Heart, Lung, and Blood Institute-funded Cardiovascular Health Study, a prospective, population-based, multicenter study on 4,815 people over age 65 whose usual dietary intake was assessed in 1989–90. During 12 years of follow-up, doctors diagnosed 980 cases of AF.
An analysis found that higher consumption of tuna fish (fresh or canned) or other fish that was broiled or baked was associated with lower incidence of AF. People who reported eating those fish one to four times per week had a 28 percent lower risk of AF, while those who had five or more servings had a 31 percent lower risk compared to those who ate fish less than once a month. In contrast, researchers found that eating fried fish or fish sandwiches (fish burgers) was not associated with lower risk of AF.
Differences in AF risk based on the kinds of fish eaten persisted after adjusting for other risk factors, including smoking, diabetes, prior stroke and high blood pressure.
Researchers assessed dietary intake through a questionnaire about usual fish consumption during the past year. In an earlier study on a subgroup of this patient population, the researchers discovered that eating tuna or other broiled and baked fish correlated to increased biomarkers of long-chain n-3 fatty acids (also called omega-3 fatty acids) in the blood while eating fried fish or fish sandwiches did not. Long-chain n-3 fatty acids are plentiful in fatty fish such as salmon, tuna, mackerel and sardines.
"The lack of correlation between fried fish and fish sandwich intake and n-3 fatty acid levels suggests that these fish meals were either mostly lean (white) fish or that the preparation method affected the n-3 fatty acid content," Mozaffarian said. "The former may be more likely because, on average, most fried fish or fish sandwiches eaten in the United States are lean (white) fish such as cod, pollock, etc."
Mozaffarian said the relationship between intake of tuna or other broiled or baked fish and AF risk should be confirmed in other studies.
The potential mechanisms of this relationship – such as effects on blood pressure, left ventricular function, inflammation, or direct anti-arrhythmic effects – should be evaluated further, he said.
Co-authors are Bruce M. Psaty, M.D., Ph.D.; Erick B. Rimm, Sc.D.; Rozenn N. Lemaitre, Ph.D., M.P.H.; Gregory L. Burke, M.D., M.S.; Mary F. Lyles, M.D.; David Lefkowitz, M.D.; and David S. Siscovick, M.D., M.P.H. The National Heart, Lung, and Blood Institute funded the research.
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