A large new study published yesterday suggests that the decline in intelligence caused by an accumulation of lead in children's blood can be at least partly reversed when steps are taken to reduce the blood levels of this toxic metal.
The study, by a research team at Albert Einstein College of Medicine in the Bronx, is the first to examine the benefits of reducing lead levels in children who have no obvious symptoms of lead poisoning.
Performance on standardized tests for cognitive development improved significantly six months after the children were treated to reduce the levels of lead in their blood and their homes were cleaned to reduce their exposure, the study found. The improvement was in direct proportion to the drop in blood lead levels, suggesting that cleansing the children's blood of lead directly resulted in better test scores.
The report, published in The Journal of the American Medical Association, is expected to encourage efforts to reduce children's exposure to lead and to identify and treat children with dangerous lead levels in their blood. But Dr. Holly Ruff, a developmental psychologist and professor of pediatrics who led the research team, said in an interview, "Our study is only suggestive, not definitive, and should be followed with more work to determine specifically which kinds of interventions would be most helpful."
The 154 children in the study, who ranged in age from 1 to 7 years, had been diagnosed with what is called moderate lead poisoning, with levels between 25 and 55 micrograms of lead per deciliter of blood. Recent studies have shown that even lower amounts can damage the developing brain and affect intelligence, and the Centers for Disease Control and Prevention in Atlanta now considers a level of 10 micrograms in children to be a matter of concern. Outward symptoms occur at much higher levels.
The latest available data shows that in 1990 eight million American children had lead levels in the danger zone of more than 10 micrograms.
The centers, a division of the United States Public Health Service, has urged states to screen all children for lead poisoning. When levels above 10 micrograms are found, the children should be periodically retested; above 15 micrograms, the agency recommends measures to reduce exposure.
The median drop over six months was seven micrograms per deciliter. On average, they found that for each three-microgram drop in lead there was a corresponding one-point improvement in the children's performance on I.Q. tests.