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Environ Health Perspect. 2008 Feb;116(2):243-8. doi: 10.1289/ehp.10424.

Blood lead concentrations < 10 microg/dL and child intelligence at 6 years of age.

Author information

1
Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA, USA.

Abstract

BACKGROUND:

Few studies provide data directly relevant to the question of whether blood lead concentrations < 10 microg/dL adversely affect children's cognitive function.

OBJECTIVE:

We examined the association between blood lead concentrations assessed throughout early childhood and children's IQ at 6 years of age.

METHODS:

Children were followed from 6 months to 6 years of age, with determination of blood lead concentrations at 6, 12, 18, and 24 months, and 3, 4, 5, and 6 years of age. At 6 years of age, intelligence was assessed in 194 children using the Wechsler Preschool and Primary Scale of Intelligence-Revised. We used general linear and semiparametic models to estimate and test the association between blood lead concentration and IQ.

RESULTS:

After adjustment for maternal IQ, HOME scale scores, and other potential confounding factors, lifetime average blood lead concentration (mean = 7.2 microg/dL; median = 6.2 microg/dL) was inversely associated with Full-Scale IQ (p = 0.006) and Performance IQ scores (p = 0.002). Compared with children who had lifetime average blood lead concentrations < 5 microg/dL, children with lifetime average concentrations between 5 and 9.9 microg/dL scored 4.9 points lower on Full-Scale IQ (91.3 vs. 86.4, p = 0.03). Nonlinear modeling of the peak blood lead concentration revealed an inverse association (p = 0.003) between peak blood lead levels and Full-Scale IQ down to 2.1 microg/dL, the lowest observed peak blood lead concentration in our study.

CONCLUSIONS:

Evidence from this cohort indicates that children's intellectual functioning at 6 years of age is impaired by blood lead concentrations well below 10 microg/dL, the Centers for Disease Control and Prevention definition of an elevated blood lead level.

KEYWORDS:

GAM; HOME; IQ; LOESS; Rochester; WPPSI-R; cohort; electrothermal atomic absorption spectrometry

PMID:
18288325
PMCID:
PMC2235210
DOI:
10.1289/ehp.10424
[Indexed for MEDLINE]
Free PMC Article
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