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

Background: Despite dramatic declines in children's blood lead concentrations and a lowering of the Centers for Disease Control and Preventions level of concern to 10 [micro]g per deciliter (0.483 [micro]mol per liter), little is known about children's neurobehavioral functioning at lead concentrations below this level.

Methods: We measured blood concentrations in 172 children at six, 12, 18, 24, 36, 48 and 60 months of age and administered the Stanford-Binet Intelligence Scale at the ages of three and five years. The relation between IQ and blood lead concentration was estimated with the use of linear and nonlinear mixed models, with adjustments for maternal IQ, quality of the home environment, and other potential confounders.

Results: The blood lead concentration was inversely and significantly associated with IQ. In the linear model, each increase of 10 [micro]g per deciliter in the lifetime average blood lead concentration was associated with a 4.6-point decrease in IQ (P=0.004), whereas for the subsample of 101 children whose maximal lead concentration remained below 10 [micro]g per deciliter, the change in IQ associated with a given change in lead concentration was greater. When estimated in a nonlinear model with the full sample, IQ declined by 7.4 points as lifetime average blood lead concentrations increased from 1-10 [micro]g per deciliter.

Conclusions: Blood lead concentrations, even those below 10 [micro]g per deciliter, are inversely associated with children's IQ scores at three and five years of age, and associated declines in IQ are greater at these concentrations than at higher concentrations. These findings suggest that more U.S. children may be adversely affected by environmental lead than previously estimated.

Canfield RL, et al. N Engl J Med, April 17, 2003; 348 (16)1517-26.

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Publication:Original Internist
Article Type:Author Abstract
Geographic Code:1USA
Date:Jun 1, 2003
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