Associations of maternal long-chain polyunsaturated fatty acids, methyl mercury, and infant development in the Seychelles Child Development Nutrition Study

Abstract

Fish consumption during gestation can provide the fetus with long-chain polyunsaturated fatty acids (LCPUFA) and other nutrients essential for growth and development of the brain. However, fish consumption also exposes the fetus to the neurotoxicant, methyl mercury (MeHg). We studied the association between these fetal exposures and early child development in the Seychelles Child Development Nutrition Study (SCDNS). Specifically, we examined a priori models of Omega-3 and Omega-6 LCPUFA measures in maternal serum to test the hypothesis that these LCPUFA families before or after adjusting for prenatal MeHg exposure would reveal associations with child development assessed by the BSID-II at ages 9 and 30 months. There were 229 children with complete outcome and covariate data available for analysis. At 9 months, the PDI was positively associated with total Omega-3 LCPUFA and negatively associated with the ratio of Omega-6/Omega-3 LCPUFA. These associations were stronger in models adjusted for prenatal MeHg exposure. Secondary models suggested that the MeHg effect at 9 months varied by the ratio of Omega-6/Omega-3 LCPUFA. There were no significant associations between LCPUFA measures and the PDI at 30 months. There were significant adverse associations, however, between prenatal MeHg and the 30-month PDI when the LCPUFA measures were included in the regression analysis. The BSID-II mental developmental index (MDI) was not associated with any exposure variable. These data support the potential importance to child development of prenatal availability of Omega-3 LCPUFA present in fish and of LCPUFA in the overall diet. Furthermore, they indicate that the beneficial effects of LCPUFA can obscure the determination of adverse effects of prenatal MeHg exposure in longitudinal observational studies.

Figure 1

Joint Effects of Prenatal MeHg and the Ω-6/Ω-3 Ratio on Estimated PDI at 9 months (left panel) and at 30 months (right panel). The points are observed values of MeHg, and the Ω-6/Ω-3 ratio. The solid lines are contours of constant PDI as estimated from the Model 5 regression at 9 months (left panel) or 30 months (right panel). Thicker lines correspond to larger values of estimated PDI. The center-most solid diagonal line in each plot is the contour corresponding to the mean PDI at the corresponding age, and shows the values of MeHg and the Ω-6/Ω-3 ratio at which the estimated PDI is predicted to be constant at its mean value. The other solid lines correspond to constant values of PDI, for PDI at its mean plus or minus twice its standard error from the model.