Effects of low-level prenatal lead exposure on child IQ at 4 and 8 years in a UK birth cohort study

摘要

Background: The association between childhood exposure to lead (Pb) and deficits in cognitive function is well established, even at low levels of exposure. The association with prenatal exposure, however, is not well understood, even though the potential adverse effects are equally important. The aim of the study was to evaluate the association between low prenatal exposure to lead and IQ in children, to determine whether there were sex differences in the associations, and to evaluate the moderation effect of prenatal Pb exposure on child IQ. Methods: Pregnant women were enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). Maternal whole blood samples collected in the first trimester were analysed for Pb (n = 4285) by ICP-MS; whole blood samples from offspring at age 30 months were analysed by AAS (n = 235). IQ was measured in 404 children at age 4 years by WPPSI and in 2217 children at age 8 years by WISC-III. Associations between prenatal blood lead concentrations (B-Pb) and child IQ were examined in covariate-adjusted linear and logistic regression model in complete cases. Moderation effects analysis was used to test the priming effect of prenatal lead exposure on lead toxicity later in childhood. Results: There was no evidence for an association of prenatal lead exposure with child IQat either 4 or 8 years old in adjusted regression models. Similarly there was no evidence that prenatal blood Pb moderated the association between child blood Pb and IQ. There was evidence of a positive association for IQ at age 8 years in girls, as shown by a sex X prenatal blood lead interaction and by a positive association in adjusted regression models stratified by sex: these models predicted an increase in verbal IQ of 0.71 points (p =0.021), performance IQ 0.57 points (p = 0.099) and total IQ 0.73 points (p = 0.017). In boys, the coefficients tended to be negative (-0.15,-0.42 and -0.29 points per 1 μg/dl increase in prenatal blood lead, respectively, but all p > 0.200). Conclusion: Prenatal lead exposure was not associated with adverse effects on child IQ at age 4 or 8 years in this study. There was, however, some evidence to suggest that boys are more susceptible than girls to prenatal exposure to lead. Further investigation in other cohorts is required.