Cognitive deficits associated with blood lead concentrations < 10 mu g/dL in US children and adolescents

Objective. Lead is a confirmed neurotoxicant, but the lowest blood lead con centration associated with deficits in cognitive functioning and academic a chievement is poorly defined. The purpose of the present study was to exami ne the relationship or relatively low blood lead concentrations-especially concentrations < 10 micrograms per deciliter (mug/dL)-with performance on t ests of cognitive functioning in a representative sample of US children and adolescents. Methods. The authors used data from the Third National Health and Nutrition Examination Survey (NHANES III), conducted from 1988 to 1994, to assess th e relationship between blood lead concentration and performance on tests of arithmetic skills, reading skills, nonverbal reasoning, and shortterm memo ry among 4.853 children ages 6-16 years. Results. The geometric mean blood lead concentration for children in the st udy sample was 1.9 mug/dL: 172 (2.1%) had blood lead concentrations greater than or equal to 10 mug/dL. After adjustment for gender, race/ethnicity, p overty, region of the country, parent or caregiver's educational level, par ent or caregiver's marital status parent, serum ferritin level, and serum c otinine level, the data showed an inverse relationship between blood lead c oncentration and scores on four measures of cognitive functioning. For ever y I mug/dL increase in blood lead concentration, there was a 0.7-point decr ement in mean arithmetic scores, an approximately 1-point decrement in mean reading scores, a 0.1-point decrement in mean scores on a measure of nonve rbal reasoning, and a 0.5-point decrement in mean scores on a measure of sh ort-term memory. An inverse relationship between blood lead concentration a nd arithmetic and reading scores was observed Tor children with blood lead concentrations lower than 5.0 mug/dL. Conclusion. Deficits in cognitive and academic skills associated vvith lead exposure occur at blood lead concentrations lower than 5 mug/dL.