Lead: devastating impact even at low levels

▸ The relation between intelligence and blood lead levels greater than 10 μg/dL is well defined: IQ declines by 2 to 5 points with every increase of 10 to 30 μg/dL. The effect of lower lead concentrations is less certain. Investigators followed 172 children from age 6 months to 5 years, measuring IQ at ages 3 and 5 years and blood lead concentration at ages 6, 12, 18, 24, 36, and 48 months.

After accounting for 9 possible confounders, including maternal IQ and home environment, each increase of 10 μg/dL in lifetime average blood lead level was significantly associated with a 4.6-point decrease from the expected IQ scores in healthy children (P=0.004) in linear analysis. When the analysis was restricted to the 101 children whose maximum blood lead level never reached 10 μg/dL, the association between higher lead concentration and lower IQ was even stronger: In a nonlinear model, IQ declined by 7.4 points with increases in the lifetime average blood lead concentrations of up to 10 μg/dL. Beyond these lower concentrations, there were further, more gradual declines (an additional 2.5-point decrease for concentrations of 10 μg/dL to 30 μg/dL). These results were unchanged whether lead exposure was categorized as peak, concurrent with testing, or average in infancy.

Comment

▸ As an editorialist notes, the CDC has repeatedly lowered its definition of elevated blood lead levels—it now stands at 10 μg/dL. It is gratifying that the median concentration in U.S. children has fallen almost 4-fold, from 15 μg/dL to 2 μg/dL since gasoline was deleaded. However, almost 500,000 children have lead levels above 10 μg/dL, and many more have levels above 2 μg/dL. What is the primary care physician to do? It is critical that infants receive enough iron, which reduces the gastrointestinal absorption of lead, and it remains important to …