A Little Lead Can Lower Kids' IQ
IQ Loss, Delayed Puberty Suggests Lead Unsafe at Any Level
"We found if you compare the amount of IQ loss over the first 10 mcg/dL, it is somewhere about three times as large as the damage that occurs from 10 to 20 mcg/dL," Canfield says. "That was one of the most surprising findings. Almost all studies have concentrated on children with blood-lead levels between 10 and 30 mcg/dL. The effects they report represented only the additional damage that occurred after levels reached 10 mcg/dL. Much more damage occurred at lower levels."
James Ware, PhD, Harvard School of Public Health, is co-author of an editorial appearing alongside Canfield's report in the April 17 issue of TheNew England Journal of Medicine. As a biostatistician, he's uncomfortable making specific conclusions based on the relatively small number of kids in the Canfield study.
"How many parents want their kids to have injury to the brain? It is an important study," Ware tells WebMD. "What's new here is this study pushes more solidly into the range that the CDC says is the threshold for concern. I don't know whether the size of this effect will turn out to be as big as they say it is. We know the country isn't devastated by lead exposure, although there is a burden of injury. I think what we know is that we can't feel good about lead levels of 10 mcg/dL."
That's not all the bad news on lead. In a second NEJM report, EPA researcher Sherry G. Selevan, PhD, and colleagues find that lead is linked to delayed puberty.
Selevan and colleagues tested lead levels and measured sexual development in 805 black girls, 781 Hispanic girls, and 600 white girls age 8 to 18. Girls with blood lead levels of 3 mcg/dL had delayed puberty compared with girls with lead levels of 1 mcg/dL. This measure is hard to interpret, however, as lead levels usually peak at age 2 and decline thereafter.
The link between lead and delayed puberty was significant for black and Hispanic girls. It was not statistically significant in white girls, although they tended to have later puberty with higher lead levels. The delay itself wasn't very long -- a matter of only a few months -- but the implications are troubling, says Selevan, a reproductive endocrinologist.