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The problem with seafood is that although it is “good for you”, it just might, on occasions and in some places, be “bad for you”. The goodness derives from its content of essential, long‐chain omega‐3 fatty acids, such as docosahexanoic and eicosapentanoic acids, which are essential for brain development. The badness would derive from toxins in fish, such as methylmercury and polychlorinated biphenyls. All fish contain methylmercury, but the only known cases of fetal damage from this source occurred in Japan half a century ago and were due to massive industrial water pollution. There has been concern, however, that in some fish‐eating populations methylmercury might impair fetal neurodevelopment. In 2004 US national guidelines were published advocating a fish intake for pregnant women of no more than 340 g (three portions) a week. Now data from the Avon Longitudinal Study of Parents and Children (ALSPAC) have suggested that such a restriction might be harmful to the fetus (Joseph R Hibbeln and colleagues Lancet 2007;369:578–85; see also Comment, ibid: 537–8).
The ALSPAC cohort was enrolled in the Bristol area in 1991–92. A total of 11875 women completed a food questionnaire at 32 weeks of pregnancy and child development was assessed from maternal questionnaires when the children were 6, 18, 30, 42 and 81 months old. At 8 years, IQ was assessed using an abbreviated form of the WISC‐IIIUK. After adjustment for multiple confounding variables, maternal seafood intake <340 g a week was associated with a significant increase in risk of low verbal IQ (lowest quartile) in the child compared with a higher intake. Among women who ate no seafood, the increase in risk was 48% and among those with a weekly intake of 1–340 g it was 9%. For low full scale IQ, the corresponding increases in risk were 29% and 19%. Low seafood intake was also associated with poorer outcomes for prosocial behaviour, fine motor skills, communication and social development.
The nutritional benefits of seafood are likely to outweigh any potential harm from its content of toxins. It is pointed out that seafood in the UK is likely to have a higher methylmercury content than in the USA, adding strength to the contention that the US advice for restricted seafood intakes during pregnancy is faulty.