Minuscule Blood Lead Levels Impair Intelligence

ITHACA, New York, April 16, 2003 (ENS) - Lead may be harmful even at very low blood concentrations, scientists from three institutions have found. The results of a five year study released today show that children with blood lead concentrations below the federal definition of an elevated lead level suffer intellectual impairment from the exposure.

The study by researchers from Cornell University, Cincinnati Children's Hospital Medical Center, and the University of Rochester School of Medicine will appear in the April 17 edition of "The New England Journal of Medicine." The research was funded by the National Institute of Environmental Health Sciences (NIEHS).

Children with blood lead levels below 10 micrograms per deciliter, the threshold currently used by the Centers for Disease Control and Prevention (CDC) to define an elevated lead level, were the focus of this study. Previous research has dealt with lead's effects in the 10 to 30 micrograms per deciliter range, still the new study finds impairments at lower lead levels.

Richard Canfield is a senior research associate at Cornell's Division of Nutritional Sciences (Photo courtesy Cornell)

The amount of impairment attributed to lead exposure was much greater than the researchers had expected, and they found that the amount of impairment attributed to lead was most pronounced at lower levels.

An additional increase in blood lead from 10 to 30 micrograms per deciliter is associated with only a small additional decline in IQ, the scientists discovered.

Charles Henderson with the Department of Human Development at Cornell explained, "Because most prior research focused on children with higher exposures than in our sample, we suspected that those investigators could estimate only the amount of additional damage that occurs after blood lead has reached 10 micrograms per deciliter - unaware that more damage may occur at lower levels."

"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 one microgram per deciliter," Canfield said.

The study followed 172 children in the Rochester, New York area whose blood lead level was assessed at six, 12, 18, 24, 36, 48, and 60 months, and who were tested for IQ at three years of age and again at five. The researchers controlled for other factors that contribute to a child's intellectual functioning, such as birth weight, mother's intelligence, income, education, and amount of stimulation in the home.

Young children are particularly susceptible to lead poisoning. (Photo courtesy National Center for Healthy Housing)

Before 1970, childhood lead poisoning was defined by a blood lead concentration greater than 60 micrograms per deciliter, the NIEHS explains. 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 one and five years is adversely 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 five micrograms per deciliter, according to CDC figures.

"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, Cincinnati Children's Hospital and director of the hospital's Children's Environmental Health Center.

"Despite a dramatic decline over the last two decades in the prevalence of children who have blood lead concentrations above 10 micrograms per deciliter, these data underscore the increasing importance of prevention," Lanphear said.

Lead based paint peeling off in chips can find its way into childrens' mouths. (Photo courtesy EPA)

"Relatively small changes in the mean IQ of a large number of children will dramatically increase the proportion of children below any fixed level of concern, such as an IQ of 80, and decrease the proportion above any gifted level such as 120," Rogan said.

Exposure to lead can happen from breathing workplace air or dust, eating contaminated foods, or drinking contaminated water. Children can be exposed from eating lead based paint chips or playing in contaminated soil. Lead in the blood can damage the nervous system, kidneys, and reproductive system.

Find lead poisoning prevention tools at: http://www.epa.gov/region1/eco/ne_lead/prevention_tools.html

Find out more about the hazards of lead at: http://www.centerforhealthyhousing.org/html/ta___t.htm