Blood Lead Levels Below "Acceptable" Value Linked With IQ Deficits, According To New Study

Bruce Lanphear, MD, MPH Children's Hospital Medical Center , Cincinnati

Contact: Jim Feuer, ph 0011 513-636-4420

Lead is toxic at concentrations in the blood that were previously thought to be harmless, according to a new study by a physician at Children's Hospital Medical Center of Cincinnati.

The study, to be presented at 1 p.m. April 30 at the Pediatric Academic Societies annual meeting, shows that IQ declines as blood lead rises in children who have a blood lead concentration lower than 10 micrograms per deciliter, the level currently considered acceptable. The lowest blood lead concentration associated with adverse effects has not yet been defined.

"This indicates that millions more children in the United States than previously thought endure the detrimental effects of lead exposure," says Bruce Lanphear, M.D., M.P.H., a physician in Cincinnati Children's division of General and Community Pediatrics and the study's main author.

Dr. Lanphear and his research colleagues studied 276 6-month-old children born in five hospitals in Rochester, NY. They measured blood lead at 6, 12, 18, 24, 26, 48 and 60 months of age. A standard IQ test (Stanford-Binet IV) was administered when the children reached 60 months. The researchers found an inverse relation of blood lead concentrations and IQ.

"Not only is there an adverse affect below currently acceptable levels, but the decline in IQ for each microgram per deciliter increase in blood lead is greater at lower levels," says Dr. Lanphear. "Among all children studied, there was on average a 5.5 point reduction in IQ for every 10 micrograms per deciliter increase in blood lead. But for children who had blood lead less than 10 micrograms per deciliter, there was an 11.1 point reduction in IQ for the initial 10 microgram per deciliter increase in blood lead."

Before 1970, lead poisoning was defined by a blood lead greater than 60 micrograms per deciliter. Since then, levels considered acceptable declined several times, before reaching the current 10 micrograms per deciliter standard. Under this definition of lead toxicity, one in every 30 children in the United States is adversely affected by lead exposure, including lowered intelligence, behavioral problems and diminished school performance.

"Despite the 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 as the consequences of lower blood lead concentrations are recognized," says Dr. Lanphear. "The results of our study argue for a reduction in blood lead levels considered acceptable to half of what they are now, or even lower. They also argue for a policy shift toward primary prevention - the elimination of residential lead hazards before children are unduly exposed."