A new study shows that prenatal exposure to tobacco smoke and exposure to lead during childhood are leading causes of increased risk of attention deficit hyperactivity disorder (ADHD) in children.

The study is published in the December issue of Pediatrics.

The data of prenatal tobacco and childhood lead exposure in the 2001-2004 National Health and Nutrition Examination Survey was analyzed by researchers which was a representative sample of U. S. children aged 8-15.

The researchers were led by Tanya E. Froehlich, MD, MS, of the department of pediatrics at Cincinnati Children's Hospital Medical Center.

Childhood exposure to lead was measured by blood samples and prenatal tobacco exposure was assessed by reports of use of cigarette during pregnancy.

The researchers found that young people exposed to tobacco in a prenatal state 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 children who were exposed to both these toxicants had an eightfold increased chance of having ADHD as compared to youths who were not exposed to either of these, according to the researchers.