Study: Even Low Lead Levels Affect Kids' IQ
Levels Studied Below Government ThresholdApr 17, 2003 | www.thewmurchannel.com
Even a little bit of lead is too much, according to a new study published in Thursday's issue of the New England Journal of Medicine.
A five-year study found that lead may be harmful even at very low blood concentrations.
Children who have blood lead concentration lower than 10 micrograms per deciliter suffer intellectual impairment from the exposure, according to researchers from Cornell University, Cincinnati Children's Hospital Medical Center, and the University of Rochester School of Medicine.
The study included 172 children in the Rochester, N.Y., area and focused on those with blood lead levels below 10 micrograms per deciliter, a threshold currently used by the Centers for Disease Control and Prevention to define an elevated lead level. Most previous research has focused on higher blood lead levels.
"In this sample of children we find that most of the damage to intellectual functioning occurs at blood lead concentrations that are below 10 micrograms per deciliter," said Richard Canfield, of the Division of Nutritional Sciences at Cornell University.
The amount of impairment attributed to lead exposure was much greater than the researchers had expected.
"We were surprised to find that in our study the IQ scores of children who had blood lead levels of 10 micrograms per deciliter were about seven points lower than for children with levels of 1 microgram per deciliter," Canfield said.
At the same time, the study found that an increase in blood lead from 10 to 30 micrograms per deciliter caused only a small additional decline in IQ.
Before 1970, childhood lead poisoning was defined by a blood lead concentration greater than 60 micrograms per deciliter. Since then, the threshold used to define an elevated blood lead level declined several times, before reaching the current value of 10 micrograms per deciliter.
Under this definition, more than one in every 50 children in the United States between the ages of 1 and 5 is affected by lead, which has been linked to lowered intelligence, behavioral problems, and diminished school performance. Nearly one in 10 young children have a lead level above 5 micrograms per deciliter, according to the CDC.
"Our study suggests that there is no discernable threshold for the adverse effects of lead exposure and that many more children than previously estimated are affected by this toxin," said Bruce Lanphear, director of the Children's Environmental Health Center at Cincinnati Children's Hospital.