HARTFORD, CONNECTICUT. An adequate daily intake of fish oils, particularly EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid, respectfully), is associated with a wealth of health benefits including decreased risk of heart disease, lower blood pressure, improvement in rheumatoid arthritis, prevention of macular degeneration, and reduced risk of type 2 diabetes. There is also evidence that fish oil consumption is beneficial for patients with depression, schizophrenia, and Parkinson's disease. Finally, several studies have confirmed that fish oils, especially DHA, are essential for optimum development of an infant's brain and visual acuity.
Thus, it is not surprising that health authorities promote the frequent consumption of fish with the American Heart Association (AHA) specifically recommending that healthy people eat fish at least twice a week. The AHA also recommends that patients with heart disease consume at least 1000 mg of EPA and DHA every day.
Unfortunately, it is becoming more and more apparent that fish consumption is not always beneficial. Gary Ginsberg and Brian Toal from the Connecticut Department of Public Health point out that many fish are now heavily contaminated with methylmercury, a highly toxic compound with profound deleterious effects on both the cardiovascular and nervous system. Many researchers have studied these adverse effects and a consensus has been arrived at as to just what amounts of methylmercury are likely to produce serious consequences. Similarly, many studies have been done to determine the minimum daily intakes of EPA and DHA needed to obtain significant benefits. The two Connecticut researchers have combined these findings into two models aimed at predicting the net health benefits of consuming particular fish and seafood. One model is concerned with determining the net benefit for adult men and women (in regard to heart disease), the other with determining the net benefits for pregnant women and infants.
The researchers looked at 13 fish and seafood specimens available fresh in Connecticut and 3 varieties of canned tuna. They found that it was safe for adults to consume unlimited amounts of tilapia, pollack, flounder, cod, shrimp, trout, herring, canned light tuna, and Atlantic salmon, although they warn that farmed salmon may not be desirable due to concerns about its possible content of carcinogens. Swordfish and shark should be totally avoided and tuna steak should be eaten no more than once a week. Canned white tuna (Albacore), halibut, sea bass, and lobster can safely be eaten twice a week. Their recommendations for pregnant women and infants are somewhat more restrictive in that consumption of canned light tuna and cod should be limited to twice a week and consumption of canned white tuna, tuna steak, halibut, sea bass and lobster should be limited to once a week.
Ginsberg, GL and Toal, BF. Quantitative approach for incorporating methylmercury risks and omega-3 fatty acid benefits in developing species-specific fish consumption advice. Environmental Health Perspectives, Vol. 117, February 2009, pp. 267- 75