Lead Exposure Affects Millions of Children and Teens in the US

Advances in the understanding of lead toxicity reveal that millions more children and adolescents in the US than previously thought suffer the detrimental cognitive effects of exposure to lead. New findings indicate that lead is toxic at much lower concentrations than we thought.

"Cognitive defects in reading, math, visual construction skills, and short-term memory, are associated with blood lead concentration considerably lower than 10 micrograms per deciliter, the level that is considered acceptable," according to a study led by Bruce P. Lanphear, MD, MPH, of Children's Hospital Medical Center of Cincinnati.

This means that more than 12.8 million US children and adolescents born between 1972 and 1988, and who have a blood lead concentration in excess of 2.5 micrograms per deciliter, are adversely affected by environmental lead exposure.

The researchers studied 4,853 children who participated in a survey between 1988 and 1994. The children, who ranged from 6 to 16 years old, participated in the National Health and Nutrition Examination Survey III, a survey of the health and nutritional status of children and adults in the United States.

The researchers found an inverse relation of blood lead concentrations and all cognitive function scores: reading, math, visual construction skills and short-term memory. This finding held true for math and reading scores at blood lead concentrations as low as 2.5 micrograms per deciliter.

Before 1970, lead poisoning was defined by a blood lead level greater than 60 micrograms per deciliter. Since then, the level considered acceptable was been lowered several times, before reaching the current 10 micrograms per deciliter standard. Under this definition of lead toxicity, one in every 20 children in the United States is adversely affected by lead exposure. This includes lowered intelligence, behavioral problems and diminished school performance.

Although blood lead concentrations below 10 micrograms per deciliter have been considered "normal" for children, contemporary levels of childhood lead exposure remain exceedingly high compared with those of pre-industrial populations. In addition, the lowest blood lead concentration associated with adverse effects has not yet been defined.

"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."

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.