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International Study Finds No Safe Level of Lead in Children's Blood

Wednesday, July 06, 2005

An international study confirms that children exposed to lead have substantial intellectual impairments, even when lead exposure is at levels well below what is currently considered harmful.

"The study indicates there is no threshold for the adverse consequences of children's exposure to lead," said Bruce Lanphear, MD, director of the Children's Environmental Health Center at Cincinnati Children's Hospital Medical Center and the study's lead author.

The study, published in the July issue of Environmental Health Perspectives, also shows that intellectual impairments at these lower levels of exposure are proportionally greater than in children with higher blood lead levels.

"We found evidence of intellectual impairments among children with blood lead levels below 10 micrograms per deciliter, the level currently considered acceptable by the Centers for Disease Prevention and Control," said Dr. Lanphear. "The study indicates that the action level set by the CDC isn't adequate to protect children.

The international group of researchers examined data from 1,333 children around the world who were followed from birth or infancy until 5 to 10 years of age. Of those children, 244 had blood lead levels of 10 micrograms per deciliter or below, and 103 had blood lead levels of 7.5 micrograms per deciliter or below.

The researchers found an inverse relationship between blood lead concentration and IQ score. The estimated IQ decrement associated with an increase of blood lead from 2.4 to 10 micrograms per deciliter was 3.9 IQ points. The decrement with an increase from 10 to 20 micrograms per deciliter was 1.9 IQ points, and from 20 to 30 micrograms per deciliter was 1.1 IQ points.

"For a given increase in blood lead, the intellectual impairment for children with a level below 7.5 was significantly larger than the impairment for children with levels above 7.5 micrograms per deciliter," says Dr. Lanphear. "Although children with a level of 20 micrograms per deciliter have, altogether, lower IQs than children with a blood lead level of 5 micrograms per deciliter, an increase in a child's blood lead level from 5 to 10 micrograms per deciliter was associated with a greater drop in IQ than an increase from 15 to 20 micrograms per deciliter."

The conclusion? Environmental lead exposure in children with blood lead levels below 7.5 is associated with intellectual impairments.

"The results of this pooled analysis underscore the increasing importance of primary prevention of childhood lead exposure," said Dr. Lanphear. "Collectively, this international analysis and other data provide sufficient evidence to eliminate childhood lead exposure by banning all non-essential uses of lead and further reducing the allowable levels of lead in air emissions, house dust, soil, water and consumer products."

Cincinnati Children's is a 423-bed institution devoted to bringing the world the joy of healthier kids. Cincinnati Children's is dedicated to transforming the way health care is delivered by providing care that is timely, efficient, effective, family-centered, equitable and safe. It ranks third nationally among all pediatric centers in research grants from the National Institutes of Health. The Cincinnati Children's vision is to be the leader in improving child health.