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Prenatal Seafood, Mercury, and Neurodevelopment

3/20/2018 2:28:29 PM
Fish and seafood provide essential omega-3 fatty acids but also neurotoxic methyl mercury, making them controversial foods during pregnancy. The European Food Safety Authority (EFSA) concluded in 2015 that the beneficial effects of seafood in the maternal diet outweigh the risk associated with methyl mercury exposure, but data from the Norwegian Mother and Child Cohort Study (MoBa) showed in 2016 that methyl mercury exposure above the 90th percentile had an adverse effect on neurodevelopment. More specifically, prenatal methyl mercury exposure of more than 2.6 micrograms per day was associated with impaired language development at age 3. A subsequent analysis of the MoBa cohort, evaluating speech and language development at age 5, was then published in 2018.
The MoBa cohort included 38,581 mother-child pairs. Maternal mercury blood concentrations at gestational week 17 were available for 2239 of the mothers. The primary exposure variable was mercury exposure, measured by maternal mercury blood level in the sub-sample and mercury dietary intake (based on food frequency questionnaires) in the whole cohort. The primary outcome was language and communication development at age 5, based on 3 scales from questionnaires: the Ages and Stages Questionnaire (ASQ), the Speech and Language Assessment Scale (SLAS), and the 20 Statement about Language-Related difficulties (Language 20).
Mean maternal blood mercury concentrations (1.03 mcg/L), mean mercury dietary intake (0.15 mcg/kg body weight/week), and mean seafood intake (217 g/week) were low in the overall cohort. Only 23% of the mothers had a seafood intake that met the recommended 300-450 grams per week.
In this cohort with generally low mercury exposure, no adverse associations were observed between mercury exposure and child language and communication skills. Instead, a favorable association was observed between increasing mercury exposure and seafood intake (up to 400 grams of seafood per week) and all three language and communication scales at age 5. Above 400 grams per week, however, the beneficial association was no longer present.    
In contrast to the results from children at the age of 3 in this same MoBa cohort, the results of the current analysis show that any adverse effects of prenatal mercury exposure on language development did not persist until age 5. The authors conclude that seafood consumption during pregnancy has an overall positive effect on child neurodevelopment, but an emphasis should remain on choosing fish and seafood that are low in mercury. 
Vejrup K, Brandlistuen RE, Brantsæter AL et al. Prenatal mercury exposure, maternal seafood consumption and associations with child language at five years. Environ Int. 2018;110 71-79.