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

BMJ 1996;312:1569-1575 (22 June)

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

Shilu Tong, doctoral student,^a Peter Baghurst, principal research scientist,^a Anthony McMichael, professor of epidemiology,^b Michael Sawyer, director,^c Jane Mudge, doctoral student ^a

^a Division of Human Nutrition, Commonwealth Scientific Industrial Research Organisation, Adelaide, SA 5000, Australia, ^b Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine, London WC1E 7HT, ^c Evaluation Unit, Women's and Children's Hospital, Adelaide, SA 5000, Australia

Correspondence to: Dr S Tong, Department of Health Services Management and Public Health, University of New England, Armidale, NSW 2351, Australia.

Abstract

Objective: To examine the association between environmentalexposure to lead and children's intelligence at age 11-13 years,and to assess the implications of exposure in the first sevenyears of life for later childhood development.
Design: Prospective cohort study.
Subjects: 375 children born in or around the lead smelting townof 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 andpostnatal blood lead concentrations. Verbal, performance, andfull scale IQ were inversely related to blood lead concentrationwith no apparent threshold. Multivariate analyses indicatedthat after adjustment for a wide range of confounders, the postnatalblood lead concentrations (particularly within the age range15 months to 7 years) exhibited inverse associations with IQ.Strong associations with IQ were observed for lifetime averageblood lead concentrations at various ages. The expected meanfull scale IQ declined by 3.0 points (95% confidence interval0.07 to 5.93) for an increase in lifetime average blood leadconcentration from 0.48 to 0.96 µmol/l (10 to 20 µg/dl).
Conclusions: Exposure to environmental lead during the firstseven years of life is associated with cognitive deficits thatseem 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 child's health and the best use of existing resources

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