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Intellectual impairment in children with blood lead concentrations below 10 microg per deciliter

Richard L Canfield1, Charles R Henderson, Deborah A Cory-Slechta

  • 1Division of Nutritional Sciences, College of Human Ecology, Cornell University, Ithaca, NY 14853, USA. rlc5@cornell.edu

The New England Journal of Medicine
|April 18, 2003
PubMed

Insights

Even low blood lead concentrations negatively impact children's IQ. This study reveals greater IQ declines at lower lead levels, suggesting more children are affected than previously thought.

Area of Science:

  • Environmental Health
  • Neuroscience
  • Pediatrics

Background:

  • Children's blood lead levels have decreased, but neurobehavioral effects below 10 µg/dL remain understudied.
  • The Centers for Disease Control and Prevention's (CDC) current level of concern for blood lead is 10 µg/dL.

Purpose of the Study:

  • To investigate the association between blood lead concentrations and neurobehavioral functioning in children.
  • To determine if lead exposure below the CDC's level of concern affects children's IQ.

Main Methods:

  • Measured blood lead concentrations in 172 children from 6 to 60 months of age.
  • Administered the Stanford-Binet Intelligence Scale at ages 3 and 5 years.
  • Used linear and nonlinear mixed models, adjusting for confounders like maternal IQ and home environment.

Main Results:

  • Blood lead concentration showed a significant inverse association with IQ.
  • A 10 µg/dL increase in average blood lead was linked to a 4.6-point IQ decrease (P=0.004).
  • IQ declined by 7.4 points as average blood lead increased from 1 to 10 µg/dL, with greater effects at lower concentrations.

Conclusions:

  • Blood lead concentrations below 10 µg/dL are inversely associated with children's IQ.
  • Declines in IQ are more pronounced at lower blood lead concentrations.
  • These findings indicate that environmental lead may affect more U.S. children than previously estimated.
Abstract

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