The study is the first to examine whether fish intake affects atrial fibrillation. It is also the first to focus on the kind of fish meals eaten, according to lead author Dariush Mozaffarian.
"The results suggest that regular intake of tuna or other broiled or baked fish may be a simple and important deterrent to atrial fibrillation among older men and women," said Mozaffarian, a researcher in the Channing Laboratory, Brigham and Women's Hospital and Harvard Medical School in Boston.
An estimated 2.3 million Americans have atrial fibrillation, and this number is expected to double during the next two decades. The prevalence of atrial fibrillation increases with age and affects about 5 per cent of those 70 years of age or older. Among the very elderly, atrial fibrillation is the single most important cause of ischemic stroke, and accounts for up to 36 per cent of all strokes in elderly people.
The chronic condition occurs when the heart's two upper chambers (the atria) quiver instead of beating effectively. This causes disability through fatigue, shortness of breath and reduced exercise tolerance. It also increases the tendency for blood to clot.
Researchers analyzed data from the US government-funded Cardiovascular Health Study, a prospective, population-based, multicenter study on 4,800 people over the age of 65, with 12 years of follow-up.
Writing in yesterday's rapid access issue of Circulation, the researchers report that higher consumption of tuna fish (fresh or canned) or other fish that was broiled or baked was associated with lower incidence of atrial fibrillation.
People who reported eating those fish one to four times per week had a 28 per cent lower risk of the condition, while those who had five or more servings had a 31 per cent 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 the condition and these differences 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 omega-3 fatty acids in the blood while eating fried fish or fish sandwiches did not.
"The lack of correlation between fried fish and fish sandwich intake and omega-3 fatty acid levels suggests that these fish meals were either mostly lean (white) fish or that the preparation method affected the omega-3 fatty acid content," Mozaffarian said.
However he added that "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 or pollock".
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.