Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis
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Lead is a confirmed neurotoxin, but questions remain about lead-associated intellectual deficits at blood lead levels < 10 姯dL and whether lower exposures are, for a given change in exposure, associated with greater deficits. The objective of this study was to examine the association of intelligence test scores and blood lead concentration, especially for children who had maximal measured blood lead levels < 10 姯dL. We examined data collected from 1,333 children who participated in seven international population-based longitudinal cohort studies, followed from birth or infancy until 5-10 years of age. The full-scale IQ score was the primary outcome measure. The geometric mean blood lead concentration of the children peaked at 17.8 姯dL and declined to 9.4 姯dL by 5-7 years of age; 244 (18%) children had a maximal blood lead concentration < 10 姯dL, and 103 (8%) had a maximal blood lead concentration < 7.5 姯dL. After adjustment for covariates, we found an inverse relationship between blood lead concentration and IQ score. Using a log-linear model, we found a 6.9 IQ point decrement [95% confidence interval (CI), 4.2-9.4] associated with an increase in concurrent blood lead levels from 2.4 to 30 姯dL. The estimated IQ point decrements associated with an increase in blood lead from 2.4 to 10 姯dL, 10 to 20 姯dL, and 20 to 30 姯dL were 3.9 (95% CI, 2.4-5.3), 1.9 (95% CI, 1.2-2.6), and 1.1 (95% CI, 0.7-1.5), respectively. For a given increase in blood lead, the lead-associated intellectual decrement for children with a maximal blood lead level < 7.5 姯dL was significantly greater than that observed for those with a maximal blood lead level = 7.5 姯dL (p = 0.015). We conclude that environmental lead sure in children who have maximal blood lead levels < 7.5 姯dL is associated with intellectual deficits.
Environmental Health Perspectives
Community Child Health