Although I believe that the diagnosis of ADHD is highly questionable because it medicalizes normal childhood behavior (see this article in Natural Life magazine as well as my blog post "Drugging Our Kids for Acting Like Kids"), we do know that children’s health (and therefore possibly their behavior) is affected by environmental pollutants. And new research from Cincinnati Children’s Hospital estimates that eliminating childhood exposure to lead and tobacco smoke could cut the incidence of behavior that qualifies for the ADHD diagnosis in the U.S. by more than a third.

Individually, each substance increases a child's risk to many types of health issues, but the researchers found that children exposed to both environmental toxins are more than eight times more likely to develop ADHD than children who weren't exposed to either substance. In the U.S. alone, 2.4 million children ages eight to 15 have been diagnosed as having ADHD.

“Tobacco and lead exposure together seem to have a synergistic, negative effect,” says Tanya Froehlich, a physician in the division of developmental and behavioral pediatrics at Cincinnati Children’s, and an author of the study, which was published in the journal Environmental Health Perspectives.

She and her colleagues found that children exposed prenatally to tobacco smoke were 2.4 times more likely to develop ADHD behavior than children who weren’t exposed. Childhood exposure to lead also increases the risk of ADHD, Froehlich says. Her research found children with the highest levels of lead exposure were 2.3 times more likely to develop behavior labeled as ADHD. And children exposed to both tobacco smoke and lead were 8.1 times more likely to exhibit ADHD behaviors than children who weren’t exposed to either toxin.

Previous studies have shown that both lead and tobacco smoke interfere with the function of dopamine, a chemical that helps transmit nerve signals in the brain.

“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 also found an estimated 1.8 million children in the United States between the ages of 4 and 15, took stimulant medications, prescribed by their doctors to supposedly help their ADHD “symptoms.”