Secondhand Smoke Boosts Kids' ADHD Risk Study says 274K cases of learning and conduct disorders could be prevented By Tim Karan, Newser Staff Posted Jul 11, 2011 4:30 PM CDT 11 comments Comments A recent study says kids exposed to second-hand smoke are 50% more likely to develop mental and behavioral disorders. (Shutterstock) (Newser) – Here's an idea for a cigarette warning label: Kids exposed to secondhand smoke at home are 50% more likely to develop mental and behavioral disorders like ADHD, according to a new study. Researchers can't prove that secondhand smoke causes the disorders, but say that if it does, 274,100 excess cases of the disorders could have been prevented, according to the Daily Mail. Researchers at the Harvard School of Public Health based their findings on a survey of 50,000 American children. They found that 6% of children under 12—meaning around 5 million kids—are exposed to passive smoking at home. Children between 9 and 11 are at the greatest risk. The study co-author says, "Health and economic burdens might be reduced significantly if voluntary smoke-free home policies are rigorously introduced."