More Evidence of the Health Benefits of Fish

Source: Tufts University
May 16, 2002 (Reviewed: April 19, 2004)

Two recent Harvard studies support the American Heart Association's advice to make fish a regular part of a heart healthy diet. As reported in the Journal of the American Medical Association and the New England Journal of Medicine, several weekly servings of fish - a prime source of omega-3 fatty acids - seem to help protect both men and women from heart disease.

Large studies support the link

A prospective, nested case-control analysis of Physicians' Health Study data utilized blood levels of omega-3 fatty acids collected at baseline from 1982 to 1984. Researchers compared the blood levels of 94 men who died suddenly of a heart attack during the 17-year follow-up period with those of 184 men matched for age and smoking status. Compared with those in the lowest quartile of omega-3 status, men in the highest quartile were more than 80% less likely to die from cardiac causes (RR=0.19, 95% CI, 0.05-0.71).

And, in a prospective analysis done over a 16-year period, women in the Nurses' Health Study who ate fish at least once a week were 28% less likely than those who rarely ate fish to suffer from heart disease (RR=0.72, 95% CI, 0.59-0.88), and 35% less likely to die of heart attack (RR=0.65, 95% CI, 0.46-0.91).

Several proposed pathways

Omega-3 fatty acids, as components of the phospholipids in cellular membranes, may help guard against cardiac death by protecting the heart cells from the effects of ventricular tachycardia. These fatty acids may also inhibit the development of heart disease by lowering triglyceride levels and by reducing platelet aggregation. There is also some evidence that omega-3s may help improve endothelial dysfunction, an indication of developing atherosclerosis.

Food sources

The body can't produce omega-3 fatty acids; they have to be consumed in foods. Cold-water fish like salmon, tuna, mackerel, and herring are particularly good sources of omega-3s, but most varieties of fish contain some fat in this form. In addition, flaxseed, canola, and soybean oils, as well as some nuts and seeds, contain alpha linolenic acid (ALA), a fatty acid that can be converted by the body into omega-3 fatty acids.

Fish oil supplements may seem to some to be an attractive alternative to eating fish, but it's not clear that taking supplements, without making any dietary changes, would have a lasting effect on heart health. Note that the participants of the Nurses' Health Study who ate the most fish also tended to eat more chicken and produce and less red meat than women who rarely ate fish, meaning that their diets were healthier for reasons other than just the added omega-3 fatty acids.

Another point to consider is that fish oil supplements can deliver a dose of omega-3s much higher than would normally be consumed in foods. Since they make the blood less likely to clot, in some cases they could do more harm than good -- an important point to bring up with patients.

Individuals who can't or won't eat fish can use canola or soybean oil, and margarine in place of other vegetable fats, or add small amounts of ground flaxseed to prepared dishes. Both options can boost omega-3 fatty acid intake in a step toward a more heart healthy diet.

Sources

• Blood levels of long-chain omega-3 fatty acids and the risk of sudden death. C. Albert, H. Campos, M. Stampfer,  et al., N Engl J Med , 2002, vol. 346, pp. 1113--1118



• Fish and omega-3 fatty acid intake and risk of coronary heart disease in women. F. Hu, L. Bronner, W. Willett,  et al., JAMA , 2002, vol. 287, pp. 1815--1821

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