Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis

TLDR

Lead is a confirmed neurotoxin, yet the extent of intellectual deficits at blood lead levels below 10 µg/dL and whether lower exposures cause proportionally greater harm remain uncertain. This study aimed to assess the relationship between blood lead concentration and intelligence test scores, focusing on children whose maximum measured levels were under 10 µg/dL. Researchers analyzed data from 1,333 children across seven international, population‑based longitudinal cohorts followed from birth or infancy to ages 5–10, using full‑scale IQ as the primary outcome. After adjusting for covariates, each rise in concurrent blood lead from 2.4 to 30 µg/dL was linked to a 6.9‑point IQ decline, with steeper decrements for children whose maximum exposure was below 7.5 µg/dL, confirming that even low‑level lead exposure is associated with intellectual deficits.

Abstract

Lead is a confirmed neurotoxin, but questions remain about lead-associated intellectual deficits at blood lead levels < 10 microg/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 microg/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 microg/dL and declined to 9.4 microg/dL by 5-7 years of age; 244 (18%) children had a maximal blood lead concentration < 10 microg/dL, and 103 (8%) had a maximal blood lead concentration < 7.5 microg/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 microg/dL. The estimated IQ point decrements associated with an increase in blood lead from 2.4 to 10 microg/dL, 10 to 20 microg/dL, and 20 to 30 microg/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 microg/dL was significantly greater than that observed for those with a maximal blood lead level > or = 7.5 microg/dL (p = 0.015). We conclude that environmental lead exposure in children who have maximal blood lead levels < 7.5 microg/dL is associated with intellectual deficits.