University of Cincinnati Children’s Center Finds Exposure to Lead and Prenatal Tobacco Smoke Linked to Attention Deficit Hyperactivity Disorder (ADHD).
Researchers from the University of Cincinnati Children’s Center have found an association between children’s blood lead levels, prenatal exposure to tobacco smoke (maternal smoking during pregnancy), and a diagnosis of ADHD. They estimate that nearly a third of ADHD cases among U.S. children ages 4 to 15 could be attributed to having either prenatal exposure to tobacco smoke or a blood lead level greater than 2.0 micrograms per deciliter (μg/dL). This could account for as much as 500,000 additional cases.
ADHD is one of the most common childhood disorders, affecting from 3 to 8 percent of U.S. children, and both genetic and environmental factors have been implicated. According to the American Academy of Pediatrics, symptoms include inattention (such as being easily distracted from work or play), hyperactivity (such as being in constant motion, squirming and fidgeting and inability to play quietly) and impulsivity (such as inability to wait, having trouble taking turns and interrupting others).
Using data on more than 4700 children from the 1999-2002 National Health and Nutrition Examination Survey (NHANES), researchers found that prenatal tobacco exposure and blood lead concentration were significant predictors of parent-reported ADHD, and found a significant dose-response relationship between lead exposure and ADHD. When the population was divided into fifths, or quintiles, compared to children in the lowest quintile of blood lead concentration, children with levels in the highest quintile were more than four times as likely to have ADHD (adjusted odds ratio or AOR = 4.1, 95% CI [confidence interval] = 1.2-14.0). Boys were nearly four times as likely as girls to have ADHD, while Mexican-American and non-Hispanic Black children had lower risks for ADHD compared to non-Hispanic white children.
Exposure to lead was associated with ADHD but no association was seen for exposure to environmental tobacco smoke after birth. While prior studies have linked prenatal exposure to tobacco smoke with ADHD, this is the first published analysis showing a significant dose-response relationship between childhood lead exposure and ADHD.
These effects were seen at a blood lead level below the 10 μg/dL threshold considered acceptable by U.S. standards. Recent findings indicate that there may not be a threshold for the effects of lead on children. Effects of childhood lead exposure include permanently lowered IQ, behavioral problems and diminished school performance.
Braun J, Kahn RS, Froehlich T, Auinger P, Lanphear B. Exposures to Environmental Toxicants and Attention Deficit Hyperactivity Disorder in US Children. Environmental Health Perspectives online 19 September 2006.
News Release from Cincinnati Children's Hospital Medical Center: Tobacco Smoke and Lead Exposure Linked to One-third of ADHD Cases