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Tobacco Smoke, Lead Exposure Increases ADHD Risk


Children who were exposed to tobacco smoke prenatally and to lead during childhood have a significantly greater risk of developing attention deficit hyperactivity disorder, or ADHD, according to a Cincinnati Children’s Hospital Medical Center study. While tobacco smoke and lead each alone increases the risk of ADHD, their combined effect magnifies it.

Attention deficit hyperactivity disorder is one of the most common childhood disorders, and it often continues through adolescence and adulthood. Symptoms include difficulty controlling behavior, trouble staying focused and paying attention, and hyperactivity. The latest statistics from the Centers for Disease Control and Prevention (CDC) note that 4.5 million children ages 5 to 17 have ever been diagnosed with ADHD, that it affects 3 to 7 percent of school-aged children, and that the disorder affects boys nearly twice as much as it does girls.

Researchers at Cincinnati Children’s Hospital Medical Center based their findings on data of 8- to 15-year-old children gathered between 2001 and 2004 from the National Health and Nutrition Examination Survey from the National Center for Health Statistics. Exposure to tobacco smoke was measured by reports of cigarette use by pregnant women, while exposure to lead was assessed using current blood lead levels. Of the 3,907 children in the study, 8.7 percent met diagnostic criteria for ADHD.

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An evaluation of the data by the investigators resulted in them estimating that up to 35 percent of ADHD cases in children ages 8 to 15, which translates into up to 800,000 children, could be reduced if exposure to tobacco smoke and lead were eliminated. Specifically, they found that children exposed prenatally to tobacco smoke were 2.4 times more likely to have ADHD, and that those who had blood lead levels in the top third had a 2.3-fold increased likelihood to have ADHD, even though levels were below the CDC’s action level of 10 micrograms per deciliter.

Among children exposed to both tobacco smoke and lead, the researchers found that the risk of ADHD was more than eight times higher when compared to unexposed children. Therefore, although tobacco smoke and lead each separately increase the risk of ADHD, children exposed to both contaminants have an even greater chance of developing the condition.

Robert Kahn, MD, MPH, the study’s senior author and a physician and researcher at Cincinnati Children’s, noted that “Although we tend to focus on ADHD treatment rather than prevention, our study suggests that reducing exposures to environmental toxicants might be an important way to lower rates of ADHD.” Women who plan to become or who are pregnant need to be informed about the potential dangers of tobacco smoke and lead exposure to their child.

Centers for Disease Control and Prevention
Cincinnati Children’s Hospital Medical Center