High Blood Lead Concentration in Older Children Associated with Lower IQ

Newswise — Blood lead concentration at the time of IQ testing is the best predictor of cognitive effects of lead exposure, according to a study published today in the May 2005 issue of the peer-reviewed journal Environmental Health Perspectives. This refutes earlier assumptions that blood lead concentration at age 2 was the best predictor of IQ scores at ages 5 and 7. While blood lead concentrations typically drop as children age, the study found a stronger association between older children's current blood lead concentration and their IQ scores, with higher blood lead correlating with lower IQ scores.

Using data from the Treatment of Lead-Exposed Children study, which began in 1994, researchers evaluated data from 780 participating children who had been regularly tested for blood lead concentration and given IQ tests from about age 2 years to about age 7.5 years. In the current study, the team examined blood lead and intelligence data from ages 2, 5, and 7 as well as other factors such as child's race and sex, and caregiver's IQ.

The amount of lead in a child's blood typically peaks at age 2, and declines with age in the U.S., as hand-to-mouth activity declines. The prevailing assumption is that most of the damage from lead exposure is done by age 2. The current results, however, indicated that blood lead concentration had the strongest association with IQ deficits in older children.

The authors acknowledged that the study has some limitations, including the fact that the children studied were much more likely than the national averages to have been exposed to lead, to be African American, to be receiving public assistance, and/or to live in single-parent households. Nevertheless, the study team concluded that continuous lead contamination significantly affects children's intelligence.

The authors emphasized the importance of testing for, monitoring, and reducing lead contamination in older children as well as younger ones. If concurrent blood lead remains important until school age for optimum cognitive development, and 6- and 7-year-olds are as sensitive or more sensitive than 2-year-olds, the authors wrote, then the difficulties in preventing lead exposure are magnified, but the potential benefit of prevention is greater.

The study team noted that if the findings are validated and accepted, it could relax an important limitation on lead studies, allowing the inclusion of older subjects who were not tested for lead exposure at age 2.

The lead author of the study was Aimin Chen of the Epidemiology Branch of the National Institute of Environmental Health Sciences (NIEHS). Other authors included Kim N. Dietrich, James H. Ware, Jerilynn Radcliffe, and Walter J. Rogan. Funding sources for the research as reported by the authors included the NIEHS in cooperation with the NIH Office of Minority Health, the Centers for Disease Control and Prevention, and McNeil Labs. The article is available free of charge at http://ehp.niehs.nih.gov/members/2005/7625/7625.html.

EHP is published by the NIEHS, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/. Brogan & Partners Convergence Marketing handles marketing and public relations for the publication, and is responsible for creation and distribution of this press release.