Benefits/risks of maternal seafood consumption

Fish and Pregnancy

BOSTON, MASSACHUSETTS. Fish is an important source of nutrients required for infant brain development with docosahexaenoic acid (DHA) being especially beneficial. Women are therefore encouraged to increase their fish consumption during pregnancy. With the ever-increasing pollution of fish habitats, including the oceans, the question arises, “Are the benefits of fish consumption outweighed by the risk of mercury contamination?” Researchers at the Harvard Medical School report the results of a study designed to examine the benefits and risks of fish and pregnancy.

Their study involved 135 women and their infants. The women completed semi-quantitative food frequency questionnaires at 26-28 weeks of gestation. The questionnaire was specifically designed to determine the consumption of various types of fish and shellfish. A hair sample was also obtained from the women immediately after delivery. At about 6 months of age the infants underwent a test (VRM) to determine their visual recognition memory, a recognized indicator of infant cognition and brain development. Together, these factors were examined to study the effects of fish and pregnancy.

The average fish consumption during the second trimester was 1.2 servings a week and the mean maternal hair mercury content was 0.55 ppm with 10% of participants having a content above 1.2 ppm. The average VRM score for the infants was 59.8. After adjusting for possible confounding variables, the researchers concluded that a higher fish consumption is associated with a higher VRM score (better cognition), with one additional fish serving a week corresponding to a 4.0 increase in VRM score.

Is Fish and Pregnancy Safe?

On the other hand, a higher maternal hair mercury content was associated with a significantly lower VRM score (poorer cognition), with a 1ppm increase in mercury corresponding to a decrease of 7.5 in VRM scoring. So is fish and pregnancy safe? The Harvard researchers conclude that women should continue to eat fish during pregnancy, but should choose varieties with low mercury levels.
Oken, E, et al. Maternal fish consumption, hair mercury, and infant cognition in a U.S. cohort. Environmental Health Perspectives, Vol. 113, October 2005, pp. 1376-80

Editor’s comment: DHA and mercury content vary widely among different species of fish. The most beneficial and safest is wild salmon with pacific sockeye salmon containing 0 ppm of mercury and 885 mg of DHA per 100 g serving. Sardines are also an excellent DHA source at 510 mg/100 g and an average mercury content of 0.013 ppm. On the other hand, canned tuna is a relatively poor source of DHA (225 mg/100 g), but a potent source of mercury (0.340 ppm). Halibut contains somewhat more DHA (375 mg/100 g), but is also fairly high in mercury (0.2 ppm). Choosing the optimum fish source is clearly important, but an easier solution to ensuring an adequate DHA intake would be to supplement with a pharmaceutical grade fish oil, which provides high quality DHA and EPA without any mercury at all.

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