Low Levels of Lead and IQ Deficits

Bruce Lanphear, MD, MPH, Cincinnati-Children's Hospital Medical Center and
Deborah A. Cory-Slechta, Ph.D., University of Rochester Medical Center
R01ES08388 and P30ES01247

Background: Among environmental hazards, lead is one of the most prevalent and dangerous to children. Lead poisoning was first recognized and described as a distinct entity 100 years ago. Since then, numerous studies have shown that blood lead concentrations above 10 micrograms/deciliter (µg/dl) are associated with adverse outcomes on intellectual development, functioning and behavior. Much of this work was supported by NIEHS and led the Centers for Disease Control and Prevention (CDC) in 1991 to set the "level of concern" for lead at 10 µg/dl. Very little data exists documenting adverse effects at concentrations below this level; however, the CDC and the World Health Organization do not recognize a threshold for lead associated deficits.

Advance: In a 5-year study of 172 children, a team of NIEHS-supported researchers from the University of Rochester, Cincinnati Children's Hospital Medical Center, and Cornell University found that lead does cause intellectual impairment at low levels. The researchers found that IQ scores for children with blood lead levels at 10 µg/dl were 7.4 points lower than for children at 1 µg/dl. Surprisingly, the study also concluded that as blood lead increased from 10 to 30 µg/dl, there was a more modest decline in IQ scores indicating that more damage occurs at lower levels for any given exposure.

Implication: The average blood lead level of children in the U.S. has been declining steadily since the removal of lead from gasoline and household paint. However, this study suggests that many more children--perhaps more than 1 out of 10--are affected by lead than previously estimated. These data emphasize the importance of prevention and add further evidence that there is indeed no safe level of lead exposure.

Citation: Canfield RL, Henderson CR Jr, Cory-Slechta DA, Cox C, Jusko TA, Lanphear BP. Intellectual impairment in children with blood lead concentrations below 10 micrograms per deciliter. N Engl J Med. 2003 Apr 17;348(16):1517-26.