Prenatal Exposure to Mercury in Fish, Impaired Neurodevelopment

Authors of a longitudinal study investigating a possible link between prenatal mercury exposure from ocean fish and impaired neurodevelopment in children report their latest findings in this week's issue of THE LANCET. The results confirm earlier findings that prenatal exposure to mercury in the Seychelles-where fish consumption is the main component of the local diet-is not associated with impaired neurodevelopment in young children.

A research team from the University of Rochester, USA, with colleagues from the Seychelles investigated 779 mother-infant pairs enrolled in the Seychelles Childhood Development Study, established in 1989/1990. Mothers reported high fish consumption-12 meals a week compared with one meal a week on average in the USA. The fish in Seychelles contained similar concentrations of methylmercury as commercial ocean fish elsewhere. Prenatal MeHg exposure was determined from maternal hair growing during pregnancy.

The investigators assessed neurocognitive, language, memory, motor, perceptual-motor, and behavioural functions in children at nine years of age. Out of 21 endpoints, only two tests were associated with prenatal methylmercury exposure: decreased performance in a motor test (the grooved pegboard using the non-dominant hand in males), and improved scores in the hyperactivity index of the Conner's teacher rating scale The investigators comment, however, that these two results probably arose by chance, and conclude that there is no evidence of neurodevelopmental risk from prenatal methylmercury exposure resulting solely from ocean fish consumption.

In an accompanying Commentary (p 1667), Constantine Lyketsos from Johns Hopkins Hospital, Baltimore, USA, concludes: "On balance, the existing evidence suggests that methyl mercury exposure from fish consumption during pregnancy, of the level seen in most parts of the world, does not have measurable cognitive or behavioural effects in later childhood...For now, there is no reason for pregnant women to reduce fish consumption below current levels, which are probably safe."