Thyroid Dysfunction as a Mediator of Organochlorine Neurotoxicity in Preschool Children.
Environ Health Perspect. 2011 Jun 30. Epub 2011 Jun 30. PMID: 21719373
Harvard School of Public Health.
BACKGROUND: Exposure to organochlorine compounds can alter thyroid function in humans, and hypothyroidism during early life can adversely affect a child's neurodevelopment. OBJECTIVES: This study aims to assess the relationship between developmental organochlorine exposures and thyroid function, and the relationship between thyroid function and subsequent neurodevelopment. METHODS: A population-based birth cohort of 182 children was followed annually up to five and a half years of age. The assessments included organochlorine compound concentrations in maternal pregnancy serum and milk, clinical thyroid parameters in maternal and cord serum, and subsequent neuropsychological outcomes of the child, along with socio-demographic cofactors. Resin-triiodothyronine uptake ratio was also assessed as an estimate of the amount of thyroxine binding globulin sites unsaturated by thyroxine. The resin-triiodothyronine uptake ratio is high in hyperthyroidism and low in hypothyroidism. RESULTS: The findings showed consistent, inverse and monotonic associations between organochlorine exposure and resin-triiodothyronine uptake ratio after covariate adjustments. No associations were observed with other thyroid parameters. Resin-triiodothyronine uptake ratio was positively associated with improved performance on most of the neuropsychological tests. For other thyroid parameters, the findings were less consistent. CONCLUSIONS: The results suggest that organochlorine compound exposures may decrease the resin-triiodothyronine uptake ratio during early life, which is a proxy measure of the binding capacity of thyroxine binding globulin. In addition, minor decreases of the thyroid function may be inversely associated with a child's neurodevelopment.