Intellectual impairment in children with blood lead concentrations below 10 microg per deciliter.
BACKGROUND
Despite dramatic declines in children's blood lead concentrations and a lowering of the Centers for Disease Control and Prevention's level of concern to 10 microg per deciliter (0.483 micromol per liter), little is known about children's neurobehavioral functioning at lead concentrations below this level.


METHODS
We measured blood lead concentrations in 172 children at 6, 12, 18, 24, 36, 48, and 60 months of age and administered the Stanford-Binet Intelligence Scale at the ages of 3 and 5 years. The relation between IQ and blood lead concentration was estimated with the use of linear and nonlinear mixed models, with adjustment 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 microg 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 concentrations remained below 10 microg 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 to 10 microg per deciliter.


CONCLUSIONS
Blood lead concentrations, even those below 10 microg 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
Richard L
RL
Division of Nutritional Sciences, College of Human Ecology, Cornell University, Ithaca, NY 14853, USA. rlc5@cornell.edu
Henderson
Charles R
CR
Cory-Slechta
Deborah A
DA
Cox
Christopher
C
Jusko
Todd A
TA
Lanphear
Bruce P
BP
D002675:Child, Preschool; D015331:Cohort Studies; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006801:Humans; D007223:Infant; D007360:Intelligence / Q000187:drug effects*; D007854:Lead / Q000009:adverse effects / Q000097:blood*; D007855:Lead Poisoning / Q000150:complications; D008297:Male; D015999:Multivariate Analysis; D012044:Regression Analysis; D013195:Stanford-Binet Test; D014481:United States
D007854:Lead