Lifetime exposure to environmental lead and children's intelligence at 11-13 years: the Port Pirie cohort study

Abstract Objective : To examine the association between environmental exposure to lead and children9s intelligence at age 11-13 years, and to assess the implications of exposure in the first seven years of life for later childhood development. Design : Prospective cohort study. Subjects : 375 children born in or around the lead smelting town of Port Pirie, Australia, between 1979 and 1982. Main outcome measure : Children9s intelligence quotient (IQ) measured at 11-13 years of age. Results : IQ was inversely associated with both antenatal and postnatal blood lead concentrations. Verbal, performance, and full scale IQ were inversely related to blood lead concentration with no apparent threshold. Multivariate analyses indicated that after adjustment for a wide range of confounders, the postnatal blood lead concentrations (particularly within the age range 15 months to 7 years) exhibited inverse associations with IQ. Strong associations with IQ were observed for lifetime average blood lead concentrations at various ages. The expected mean full scale IQ declined by 3.0 points (95% confidence interval 0.07 to 5.93) for an increase in lifetime average blood lead concentration from 0.48 to 0.96 µmol/l (10 to 20 µg/dl). Conclusions : Exposure to environmental lead during the first seven years of life is associated with cognitive deficits that seem to persist into later childhood. Key messages Few longitudinal data have yet been reported on the time course of the effects of exposure to environmental lead Exposure to environmental lead early in life is associated with cognitive deficits that persist into middle childhood The duration, intensity, and timing of exposure to lead, as well as other social and familial factors, may influence the nature and degree of reversibility The formulation of a public health policy for preventing any possible effects of lead exposure should be based on a composite consideration of the child9s health and the best use of existing resources