Two scientific reviews of the health effects of dietary fish
Two scientific reviews of the health effects of dietary fish intake probably made bigger splashes than expected by being released on the same day.

Earlier this week, the Institute of Medicine (IOM) released Seafood Choices: Balancing Benefits and Risks, its summary of current knowledge on the health benefits of eating fish and the potential risks from contaminants such as methylmercury, dioxins, and polychlorinated biphenyls (PCBs) [1]. The same day, a literature review on much the same topic was published by the Journal of the American Medical Association [2].

Both documents offer positive messages about the health effects of the n-3 polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) abundant in fish and other seafood. The IOM report arrives at no firm conclusions about whether the regular consumption of fish will prevent disease. The JAMA report's authors, however, appear certain that its health benefits outweigh any risks.

As covered by heartwire earlier this week, Dr Dariush Mozaffarian (Harvard School of Public Health, Boston, MA) and Dr Eric B Rimm (Brigham and Women's Hospital, Boston, MA) found that intake of EPA and DHA equivalent to one or two servings of fish per week was associated with a 36% decrease in the risk of death from coronary heart disease (p<0.001) and a 17% drop in total mortality (p=0.046). They also concluded that the n-3 PUFAs are likely important to early brain development. Those benefits far outweigh any risks from contaminants, they write.

"Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess CHD deaths annually and suboptimal neurodevelopment in children," they write.

The IOM report's dietary recommendations are more circumspect and less concrete. The document "confirms that eating fish and shellfish may reduce people's overall risk for developing heart disease," according to a press release from the organization [3]. "It is not certain whether this is because substituting the lean protein of seafood for fatty cuts of meat reduces consumers' intake of saturated fat and cholesterol or because of the protective effects of omega-3 fatty acids. . . . The report also found evidence that maternal consumption of omega-3 fatty acids through seafood can contribute to vision and cognitive development in infants and lengthen the duration of gestation."

The report acknowledges potential risks from methylmercury, dioxins, and PCBs but notes, according to the IOM statement, that "reliable data on the distribution of some contaminants is lacking, and there is little evidence on how beneficial effects of seafood might counteract some of the risks from contaminants."

Both reports include caveats about contaminant exposure and fish intake for special populations, particularly women of childbearing age or who are nursing, and cautions for people who fish and eat their own catch from potentially polluted inland waters.

More than 400 pages long and designed to help the US government communicate these issues to the public, the IOM report is noteworthy for observing how little is actually known about either the benefits or the risks of consuming fish and for identifying knowledge gaps that can help guide future research. The IOM, an arm of the National Academy of Sciences (NAS), a nonprofit corporation, describes itself as "an adviser to the federal government on issues of medical care, research, and education."

The differences and similarities of the IOM and JAMA....