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Am Fam Physician. 2007;75(5):728-731

Background: Although fish consumption has been shown to benefit cardiovascular risk, there has been concern about the adverse effects of toxins found in fish, notably dioxins, polychlorinated biphenyls (PCBs), and mercury. This review by Mozaffarian and Rimm was a risk-benefit analysis of fish consumption focusing on: (1) cardiovascular effects of fish and fish oil; (2) effects of mercury and fish oil on infant brain development; (3) effects of mercury on adult neurologic outcomes and cardiovascular risk; and (4) toxic effects of PCBs and dioxin.

Recommendations: Prospective randomized trials support the cardiovascular benefit of fish consumption, particularly oily fish. Up to a threshold of about 250 to 500 mg per day, without additional benefit at higher doses, modest fish consumption reduces mortality from coronary heart disease by about one third. Reduction of mortality risk in a mixed population is estimated to be 14 to 17 percent—similar to the benefits of statin medications. Consumption of fish and fish oil during pregnancy has been shown to be beneficial for infant neurodevelopment.

Methylmercury, which is readily absorbed into the tissues, is known to cause serious neurologic abnormalities in children after high exposure during gestation. However, the effect of U.S. maternal fish consumption on infant neurologic development is controversial, with benefits found with fish consumption and negativeeffects correlating with mercury levels (as measured in hair). An Environmental Protection Agency (EPA) advisory recommended limiting mercury consumption to 0.1 mcg per kg per day and avoiding fish containing higher levels of mercury.

A negative effect of mercury on cardiovascular risk has not been established but, if present, appears not to outweigh the benefits. Although high levels of mercury affect neurologic function in adults, mostly causing paresthesias, there is scant reliable evidence that lower mercury levels impair cognition and other neurologic functions. There is better evidence of a positive effect of fish consumption on neurologic problems such as dementia and depression.

Digoxin and PCBs are found in meat, dairy products, and vegetables. Fish do not contain greater amounts of these substances than other foods. The risk of dying of heart disease by not consuming fish is much greater than the cancer mortality risk from fish consumption. Limiting salmon consumption to one 6-oz serving per week maintains the cardiovascular benefits while reducing lifetime cancer risk.

Conclusion: Women who are pregnant, nursing, or contemplating pregnancy should limit their consumption of albacore tuna to 6 oz per week but should consume at least 12 oz of other fish weekly for adequate benefits.

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Copyright © 2007 by the American Academy of Family Physicians.

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