Omega-3 fatty acids, mercury, and selenium in fish and the risk of cardiovascular diseases

Fish consumption is associated with lower risk of cardiovascular disease. Some fish species also contain methylmercury, which may increase cardiovascular risk, as well as selenium, a trace element that could counter the effects of methylmercury or have beneficial effects itself. These potentially conflicting effects have created public confusion about the risks and benefits of fish consumption in adults. We examined the evidence for cardiovascular effects of fish consumption, particularly effects of marine omega-3 fatty acids, methylmercury, and selenium. Compelling evidence indicates that modest fish consumption substantially reduces cardiovascular risk, in particular cardiac mortality, related at least partly to benefits of omega-3 fatty acids. In contrast, observational studies and (for selenium) clinical trials demonstrate mixed and inconclusive results for cardiovascular effects of methylmercury and selenium. Net health benefits of overall fish consumption in adults are clear. Quantitative risk-benefit analyses of cardiovascular effects of consuming specific fish species, based on joint contents of fatty acids, methylmercury, and selenium, cannot currently be performed until the cardiovascular effects of methylmercury and selenium are established.