'Safe' Lead Levels Lower IQ in Children, Study Finds

Blood levels of lead below current federal and international guidelines of 10 micrograms per deciliter produce a surprisingly large drop in IQ of up to 7.4 points, a U.S. team reports in today's New England Journal of Medicine. Researchers estimate that one in every 50 U.S. children has lead levels above that guideline and that one in every 10 has levels of 5 micrograms/deciliter or above -- well within the dangerous range.

"People have been asking, 'How low [a lead concentration] is low enough?' " said Dr. Richard Canfield of Cornell University, one of the leaders of the study. "The fact is, in our study, we found no evidence for a safe level. There is no safe level of exposure."

The findings "reflect the growing opinion that low levels of lead are more toxic than we thought," said Dr. Herbert A. Needleman, a prominent lead researcher who was not involved in this study. "When we took the lead out of gasoline

An estimated 38 million houses built before 1950 still have lead-based paints on their walls. In California, exposure also comes from folk medicines and Mexican ceramic pottery. "There is a message for parents in here that goes beyond whatever government policy recommendations should be," Canfield said. Just as parents should protect their children from the effects of smoking and alcohol use, they "should be aware of sources of lead in their environment and, most important, should try to engage in some type of cleanup or abatement so the child never comes in contact with lead."

In a separate paper in the journal, researchers from the Environmental Protection Agency also found that low levels of lead delay puberty for several months in young girls, especially African Americans and Latinas.

Although delaying puberty is not necessarily harmful, the findings suggest that lead is interfering with critical hormonal processes during development.

"That fits in with the increased interest in general with the idea that environmental chemicals can be endocrine disruptors," said Dr. David Bellinger of Harvard Medical School. "Lead has not been considered as prominently as other chemicals. This suggests that we ought to be looking at it more closely."