The study is published in the December issue of Pediatrics.
Researchers led by Tanya E. Froehlich, MD, MS, of the department of pediatrics at Cincinnati Children's Hospital Medical Center, analyzed data of prenatal tobacco and childhood lead exposure in the 2001-2004 National Health and Nutrition Examination Survey, a representative sample of U.S. children aged 8 to 15.
Prenatal tobacco exposure was measured by reports of cigarette use during pregnancy, and childhood lead exposure was assessed by blood levels.
The researchers say they found that young people exposed prenatally to tobacco smoke were 2.4 times more likely to have ADHD, and that those with blood levels in the top third of the population had a 2.3-fold increased likelihood of ADHD diagnosis.
The combined effect from both toxicants was even greater. Children with both exposures had a more than eightfold increased chance of having ADHD, compared to youths who weren't exposed to either, the researchers say.
The authors say their study is the first to determine the independent effects of tobacco smoke and lead on ADHD in a nationally representative sample, and contend it provides the first estimate of joint effects of the two common toxicants.
The researchers examined data on 2,588 youngsters from the National Health and Nutrition Examination Survey 2001-2004 and 8.7% met criteria for diagnosis with ADHD. "Our findings suggest that reduction of toxicant exposures may be an important avenue for ADHD prevention and they underscore the enormous burden that may be associated with continued exposure to tobacco and lead,'' the researchers conclude.