Beneficial roles of selenium and docosahexaenoic acid against prenatal methylmercury-induced adverse effects on child neurodevelopment: The Tohoku Study of Child Development at 42 months.

Because prenatal exposure to methylmercury (MeHg) adversely affects child development, leading to recommendations to limit fish consumption during pregnancy. Nonetheless, fish is rich in nutrients such as n-3 polyunsaturated fatty acids, including docosahexaenoic acid (DHA) and selenium (Se), which are essential for neurodevelopment. This study examined the associations of combined prenatal exposure to MeHg, DHA, Se and lead on the intelligence quotient of 42-month-olds. Intellectual ability was assessed in 471 children (239 male and 232 female) using the Kaufman Assessment Battery for Children (K-ABC). Associations between biomarkers and K-ABC scores were evaluated using multiple regression, Bayesian kernel machine regression (BKMR), and quantile g-computation. The median maternal hair total mercury (THg) concentration was 2.5 μg/g (5th-95th percentile, 1.0-5.9 μg/g). The median levels of maternal plasma DHA and cord-plasma Se were 168.8 (98.9-256.5) μg/mL and 65.8 (51.0-83.5) ng/g, respectively. In multiple regression analyses, maternal hair THg was significantly negatively associated with simultaneous and mental processing scores in males only, whereas maternal plasma DHA was marginally positively associated with the simultaneous processing score and significantly positively associated with the mental processing score in males. Cord-plasma Se showed marginal positive associations with both processing scores in males. In contrast, quantile g-computation and BKMR analyses showed no overall association between combined exposure and K-ABC score. These findings suggest that prenatal biomarker levels of MeHg, DHA, and Se were differentially associated with early cognitive development, highlighting the importance of balancing risks and benefits related to fish consumption during pregnancy.