Objective: To examine the association between environmental exposure to lead and children's 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: Children's 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 mumol/l (10 to 20 micrograms/dl).
Conclusion: Exposure to environmental lead during the first seven years of life is associated with cognitive deficits that seem to persist into later childhood.