Some 2 million Americans suffer from atrial fibrillation, a condition in which part of the heart beats irregularly instead of pumping rhythmically, the way it's supposed to. Researchers at several universities looked at diet and risk of atrial fibrillation.

What the researchers wanted to know: Does eating tuna and other baked or broiled fish decrease the risk of atrial fibrillation?

What they did: Researchers used the Cardiovascular Health Study, a long-term study of all sorts of factors that could alter the risk of cardiovascular disease. In 1989 and 1990, 5,200 men and women over 65 were randomly chosen from Medicare lists in four communities. Each person answered questions on how often they eat different foods, their medications, health, education, smoking, and so on. They also had tests done, including, in 65 people, blood tests for two omega-3 fatty acids. After all that baseline testing was done, each participant had a checkup every year, and the researchers kept up with their health through hospital records.

What they found: People who ate tuna or other nonfried fish five or more times a week were less likely to develop atrial fibrillation than people who ate such food rarely, while people who ate fried fish or fish sandwiches once a week were at higher risk. These results held even after adjusting for lots of characteristics, including demographics, health, lifestyle, and diet other than fish. Among the very small group that had blood tests for omega-3 fatty acids, those who ate tuna and other fish had higher levels (but not those who ate fried fish or fish sandwiches—probably because they're made with leaner fish).

What the study means to you: Pay no mind to the person in the cubicle next to you—you pop that stinky can of tuna open! Go ahead! It's for your heart!

Caveats: Finding an association between fish consumption and heart health doesn't prove that one causes the other; they could both be related to something else, although the researchers took a lot of other factors into consideration. Also, people might have changed their fish-eating habits between the beginning and end of the 12-year study.

Find out more: American Heart Association explains atrial fibrillation and recommends fish. Many people are concerned about mercury in fish, and the Environmental Protection Agency and Food and Drug Administration have advised women who are pregnant (or might become pregnant) or nursing to avoid eating too much fish that might contain mercury.

Marine biologists are pretty sure that a lot of fish populations are being fished into oblivion, so the Monterey Bay Aquarium has advice on how to eat seafood in an environmentally sensitive way.

Read the article: Mozaffarian, D. et al. "Fish Intake and Risk of Incident Atrial Fibrillation." Circulation. July 27, 2004, Vol. 110, pp. 368–373.

Abstract online: http://circ.ahajournals.org/