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

BACKGROUND The association between childhood exposure to lead (Pb) and deficits in cognitive function is well established. The association with prenatal exposure, however, is not well understood, even though the potential adverse effects are equally important. OBJECTIVES 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 Whole blood samples from pregnant women enrolled in ALSPAC (n=4285) and from offspring at age 30 months (n=235) were analysed for Pb. Associations between prenatal blood lead concentrations (B-Pb) and child IQ at age 4 and 8 years (WPPSI and WISC-III, respectively) were examined in adjusted regression models. RESULTS There was no association of prenatal lead exposure with child IQ at 4 or 8 years old in adjusted regression models, and no moderation of the association between child B-Pb and IQ. However, there was a positive association for IQ at age 8 years in girls with a predicted increase in IQ (points) per 1μg/dl of: verbal 0.71, performance 0.57, total 0.73. In boys, the coefficients tended to be negative (-0.15, -0.42 and -0.29 points, respectively). 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.