Fish: A Good Catch?
by Dana Denis, MSPH., RD (topic expert: nutrition)

Fish and shellfish are an excellent source of nutrition and an important part of a heart-healthy diet. They are rich in omega-3 fatty acids, vitamins, minerals and protein. The benefit of fish in relation to cardiovascular disease is well documented and the American Heart Association recommends including fish in your diet at least twice a week.

Even with these benefits, an area of concern has surfaced.

Mercury in our environment

Mercury is a naturally occurring element in the environment. It is also produced as a result of industrial pollution. Mercury is released into the air and it drops back down to earth in rainwater and can build up in soil and waterways. Mercury present in the water is converted to methylmercury, which is the most toxic form of mercury. It accumulates in the food chain and is present in the highest quantities in long-lived predatory fish, such as shark and swordfish.

Methylmercury toxicity

Long-term exposure to methylmercury affects the brain and central nervous system and produces neurological symptoms. So far there have been no reported cases of overt toxicities from fish in the United States.

Studies evaluating the association between mercury levels and heart disease have produced conflicting results. However, even if mercury reduces the beneficial effect of consuming fish, it does not appear to increase overall risk. Obviously, more research is necessary.

Prenatal Risk

DHA (docosahexaenoic acid) present in fish has been shown to positively affect neurological development in infants and small children. Studies show that increased maternal intake of fish resulted in higher scores for behavioral attention, recognition and memory, and language comprehension in infants. However, the developing fetus is also at increased risk for mercury toxicity. Methylmercury crosses the placenta and affects fetal brain development and can cause subtle neurological effects. Mercury can also pass through to breast milk. Due to this increased risk, in March 2004, the Environmental Protection Agency (EPA) and the Department of Health and Human Services (DHHS) issued recommendations for women who are pregnant or might become pregnant, nursing mothers and young children limiting consumption of specific types of fish.

The recommendations are:

Children

Young children should follow the same guidelines as those for pregnant women. Kids tend to like tuna and shrimp, which can contain low amounts of mercury if you choose light tuna rather than albacore tuna. The commercially prepared breaded fish products, like fish sticks, are also favorites and usually contain low levels of mercury. Remember children are smaller individuals so their portion sizes are also smaller, which reduces exposure to mercury.

Additional Information

The Physicians for Social Responsibility (PSA) and the Association of Reproductive Health Professionals have teamed up to provide their recommendations on a safe level of fish consumption. They recommend that the EPA add a moderate mercury level category and expand their advice to include safe levels of consumption (once a week) for those fish. Their website contains a clip and save "wallet card" that clearly groups fish by level of mercury, identifies those at risk for PCB (polychlorinated biphenyls) contamination as well as those that are currently being "over-fished". http://www.mercuryaction.org/fish/images/wallet-card.pdf.

Achieve Balance

The positive effects of a diet that includes fish must be weighed against the potential risk of contamination. Pregnant and nursing women, women planning to become pregnant and children should not eliminate fish due to the potential benefits of DHA; however, they should follow the recommendations reviewed above. Choosing from a variety of fish will reduce risk and continue to allow the health benefits. Being aware of fish that have higher mercury levels is the first step to providing balance and minimizing exposure. More research is necessary to fully assess whether the levels of mercury consumed in a diet rich in fish and shellfish produces a risk in healthy adults. For more detailed information on the mercury level of a fish you enjoy eating go to the FDA website at: http://www.cfsan.fda.gov/~frf/sea-mehg.html.

References:

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4. Food and Drug Administration. Mercury levels in commercial fish and shellfish. Available at: www.cfsan.fda.gov/~frf/sea-mehg.html. Accessed on August 6, 2004 and May 13, 2007.
5. Food and Drug Administration. What you need to know about mercury in fish and shellfish. Available at: http://www.cfsan.fda.gov/~dms/admehg3.html. Accessed August 6, 2004 and May 6, 2007.
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