Background: Fish are important sources of protein and contain a variety of nutrients, such as n-3 long-chain polyunsaturated fatty acids (PUFA), essential for normal brain development. Nevertheless, all fish also contain methyl mercury (MeHg), a known neurotoxicant in adequate dosage. Our studies of the Seychelles Child Development Study (SCDS) Main Cohort enrolled in 1989-1990 (n=779) have found no consistent pattern of adverse MeHg effects at exposures achieved by daily fish consumption. Rather, we have observed evidence of improved performance on some cognitive endpoints as prenatal MeHg exposure increases in the range studied. These observations cannot be related to MeHg and may reflect the role of unmeasured covariates such as essential nutrients present in fish. To determine if these associations persist into young adulthood, we examined the relationship between prenatal MeHg exposure, recent PUFA exposure and subjects' neurodevelopment and behavior at 19 years of age.
Methods: We examined 533 participants using the following test battery: the Profile of Mood States-Bipolar (POMS-Bi); Finger Tapping; Kaufman Brief Intelligence Test (K-BIT); measures of Fine Motor Control and Complex Perceptual Motor Control; and Visual Spatial Contrast Sensitivity. We collected the following covariates: maternal IQ, family life course stressors, socioeconomic status, and subjects' recent postnatal MeHg, sex, and computer use. Primary analyses (based on N=392-475) examined covariate-adjusted associations in multiple linear regression models with prenatal MeHg as the primary exposure measure. Secondary analyses additionally adjusted for total n-6 and fish-related n-3 PUFA measured in the subjects' serum at the 19-year examination.
Results: Study participants had a mean prenatal MeHg exposure of 6.9 ppm, and a mean recent postnatal exposure of 10.3 ppm. There were no adverse associations between prenatal MeHg and any of the measured endpoints. For recent postnatal MeHg exposure, however, adverse associations were observed for Finger Tapping (non-dominant hand) among women and for the K-BIT Matrices for both sexes, with or without adjustment for PUFA.
Conclusion: Our findings continue to provide no evidence for an adverse effect of prenatal MeHg exposure on development in a cohort that consumes fish daily. Observations for postnatal MeHg exposure will need to be confirmed using more comprehensive exposure measures.
Keywords: Child development; Methyl mercury; Prenatal exposure.
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