Food and Behaviour Research

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Maternal Fish Consumption, Hair Mercury, and Infant Cognition in a U.S. Cohort

Oken E, Wright RO, Kleinman KP, Bellinger D, Amarasiriwardena CJ, Hu H, Rich-Edwards JW, Gillman MW. (2005) Environmental Health Perspectives 113, 10 1376-80 

Web URL: Read or download the full text of this paper at Environmental Health Perspectives here


Fish and other seafood may contain organic mercury but also beneficial nutrients such as n-3 polyunsaturated fatty acids. We endeavored to study whether maternal fish consumption during pregnancy harms or benefits fetal brain development.

We examined associations of maternal fish intake during pregnancy and maternal hair mercury at delivery with infant cognition among 135 mother-infant pairs in Project Viva, a prospective U.S. pregnancy and child cohort study. We assessed infant cognition by the percent novelty preference on visual recognition memory (VRM) testing at 6 months of age.

Mothers consumed an average of 1.2 fish servings per week during the second trimester. Mean maternal hair mercury was 0.55 ppm, with 10% of samples > 1.2 ppm. Mean VRM score was 59.8 (range, 10.9-92.5). After adjusting for participant characteristics using linear regression, higher fish intake was associated with higher infant cognition. This association strengthened after adjustment for hair mercury level: For each additional weekly fish serving, offspring VRM score was 4.0 points higher [95% confidence interval (CI), 1.3 to 6.7]. However, an increase of 1 ppm in mercury was associated with a decrement in VRM score of 7.5 (95% CI, -13.7 to -1.2) points. VRM scores were highest among infants of women who consumed > 2 weekly fish servings but had mercury levels = 1.2 ppm.

Higher fish consumption in pregnancy was associated with better infant cognition, but higher mercury levels were associated with lower cognition. Women should continue to eat fish during pregnancy but choose varieties with lower mercury contamination.


Much publicity has been given to the possible risks from mercury in fish and seafood, leading to dietary advice in both the US and UK that women should restrict their intake during pregancy. No consideration was given to the potential benefits of seafood consumption when this advice was formulated.

Fish and seafood are the main natural dietary sources of the long-chain omega-3 fatty acids required for normal brain development, so it makes sense to consider the overall balance of benefits to possible risks, as this study set out to do.

Here, it was found that higher maternal intakes of fish and seafood during pregnancy are associated with better outcomes for children's cognitive development. The same finding emerged from a much larger study subsequently carried out using data from a large UK birth cohort study. See: