Recent Developments in Low-Level Lead Exposure and Intellectual Impairment in Children

Karin Koller; Terry Brown; Anne Spurgeon; Len Levy

Disclosures

Environ Health Perspect. 2004;112(9) 

In This Article

Cross-Sectional Studies

Cross-sectional studies form part of a worldwide effort to quantify the effects of lead exposure in children. The main limitation of such cross-sectional studies is that they measure blood lead at one specific time point only. Because the half-life of lead in blood approximates that of the erythrocyte (approximately 35 days), it is primarily an indicator of recent exposure. This is of particular importance with lead exposure, as blood lead levels peak in children at around 2 years of age.

We identified eight recent cross-sectional studies looking at the relationship between blood lead concentrations and children's cognitive abilities: the large U.S. National Health and Nutrition Examination Survey (NHANES) III (Lanphear et al. 2000) and seven studies from six different countries [Croatia, Denmark, Saudi Arabia, Mexico, Pakistan, and Taiwan (Al-Saleh et al. 2001; Calderón et al. 2001; García-Vargas et al. 2002; Nielsen et al. 2000; Prpic-Majic et al. 2000; Rahman et al. 2002; Wang et al. 2002)]. All studies examined children 6 years of age or older (range 6-16 years) but differed in sample size (80-4,853) and the number of confounders considered. Mean blood lead levels ranged from 2.94 to 9.73 µg/dL. It was unfortunate that the very large NHANES III study (4,853 children) lacked data on two key confounders: home environment and maternal IQ. There was no consistent effect of blood lead levels on cognitive function across these studies, and taken together we believe they add little to the current debate on low lead exposure and its effect on cognition.

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