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Tobacco Smoke and Lead Exposure Linked to One-third of ADHD Cases

Thursday, October 05, 2006

A new study finds that prenatal exposure to tobacco smoke and childhood exposure to lead account for about one-third of Attention Deficit Hyperactivity Disorder (ADHD) cases among children in the United States.

The study, conducted by researchers at Cincinnati Children's Hospital Medical Center, will be published online Tuesday September 19 in the journal Environmental Health Perspectives.

"Our analysis confirms a suspected link between prenatal tobacco exposure and ADHD, and it demonstrates that the greater the level of blood lead, the greater the risk of ADHD," says Bruce Lanphear, MD, director of the Children's Environmental Health Center at Cincinnati Children's and corresponding author of the study. "These findings underscore the profound behavioral health impact of these prevalent exposures and highlight the need to strengthen public health efforts to reduce prenatal tobacco smoke exposure and childhood lead exposure."

The researchers found that more than 8 percent of children in the study had doctor-diagnosed ADHD. Of these children, 4.8 percent, or an estimated 1.8 million children in the United States between the ages of 4 and 15, took stimulant medications.

The investigators found approximately 270,000 cases of ADHD attributable to mothers smoking during pregnancy. Children exposed to tobacco prenatally had a 2.5-fold higher risk of ADHD compared to children not exposed to tobacco prenatally.

Even more cases of ADHD, approximately 290,000, were attributable to childhood lead exposure as measured by a blood lead test. Children with a blood lead concentration greater than two micrograms per deciliter had a four-fold higher risk of ADHD compared to those in the lowest quintile -- below .8 micrograms per deciliter.

The study is based on data gathered between 1999 and 2002 from a parent or guardian of 4,704 children. These children were between the ages of 4 and 15 and had participated in the National Health and Nutrition Examination Survey (NHANES), which was conducted by the National Center for Health Statistics at the Centers for Disease Control and Prevention. NHANES is designed to collect information about the health and diet of people in the United States.

The Centers for Disease Control and Prevention considers blood lead concentrations lower than 10 micrograms per deciliter as being acceptable. Studies by Dr. Lanphear, however, including one published in The New England Journal of Medicine in 2003, show that lead is toxic at concentrations in the blood that were previously thought to be harmless.

The lead author of the study was Joe Braun, formerly affiliated with the College of Nursing at the University of Wisconsin-Milwaukee.

Cincinnati Children's is a 475-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. Cincinnati Children's ranks second nationally among all pediatric centers in research grants from the National Institutes of Health. It is a teaching affiliate of the University of Cincinnati College of Medicine. The Cincinnati Children's vision is to be the leader in improving child health.