That advice emerges from two studies affirming the beneficial value of fish in the diet in preventing the kind of blockage of arteries that leads to heart attacks and to strokes.
And while both studies come from Boston, "the land of the bean and the cod," cod is not high on the list of the best fish to eat. That's because the benefit comes from the omega-3 fatty acids, also called polyunsaturated fatty acids (PUFAs), says Dr. JoAnn E. Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital and a co-author of the study that appears in tomorrow's issue of the Journal of the American Association.While eating cod is not a bad idea, fish that are especially rich in PUFAs are mackerel, salmon, sardines -- and tuna, Manson says.
Researchers have long noticed that groups of people who eat lots of fish have a lower death rate from heart disease; in Alaska, it's known as the "Eskimo paradox."
The findings, based on analysis of the 16-year Nurses Health Study of nearly 85,000 women, found a neat relationship between fish intake and the risk of heart disease and death. Women who ate fish one to three times a month reduced that risk by 21 percent, compared to those who had less than one serving of fish each month.
The risk is lower progressively as fish intake increases, with a reduction of 34 percent for more than five fish meals a week, but the significant reduction can come from just that one tuna sandwich a month, Manson says.
"There appear to be three mechanisms by which the long-chain, omega-3 fatty acids act," Manson says. "One, there is a favorable effect on blood cholesterol. Two, there is a lowering of the tendency for blood clots. Three, there is also an effect on heart rhythm, a reduction in harmful arrhythmias."
The study does break some new ground, Manson says, because it is "the first large-scale study of fish intake and the risk of heart disease in women. The risk has been studied primarily in men, but the findings apply to both sexes."
The newest report on men, also from Brigham and Women's Hospital, concerns the Physicians' Health Study, which has followed 22,000 male doctors for more than 17 years. It looked at blood levels of PUFAs and found them "strongly associated with a reduced risk of sudden death among men without evidence of prior cardiovascular disease." That study will appear in the April 11 issue of the New England Journal of Medicine, and was released a day early to coincide with the Nurses Health Study report.
Both studies come on the heels of an Italian report saying that daily supplements of PUFAs cut the risk of sudden death by half. Right now, the American Heart Association says it's best to get PUFAs from fish, rather than supplements.
Both American studies and the one from Italy will be considered when the heart association's nutrition committee meets next week, says Dr. Alice H. Lichtenstein, professor of nutrition at Tufts University and vice chairwoman of the committee. It's not possible to predict what the committee will decide, and any change in recommendations probably will not come quickly, she says.
"We will reconsider the position," Lichtenstein says. "Prior to this, there has not been enough data to make a recommendation on fish oil supplements. Now we have to go back and look at the new data."
What To Do
"Eating fish is an extremely low-risk and low-cost strategy toward reducing the risk of heart disease," Manson says. "And we previously found a reduced risk of stroke and a possible association with a reduced risk of diabetes and some immune diseases."
The fish story is told by the American Heart Association.
Fish isn't for everyone. If you're pregnant or considering becoming pregnant, the government says you should limit your consumption of some fish because it may contain mercury. The U.S. Food and Drug Administration has warned about specific kinds of fish, including king mackerel, swordfish, shark and tilefish.