DURHAM, N.C., Dec. 26 (UPI) -- North Carolina researchers are investigating the relationship between exposure to tobacco smoke during pregnancy and attention-deficit/hyperactivity disorder.
Susan K. Murphy, an associate professor of obstetrics and gynecology at Duke University School of Medicine and the Center for Study of Neurodevelopment and Improving Children's Health following Environmental tobacco Smoke exposure at Duke said secondhand smoke is known to be an environmental risk factor for ADHD.
ADHD affects over 5 million children in the United States and costs the country $42.5 billion each year, a 2007 study found.
"A recent study suggests that up to half of U.S. children are exposed to secondhand smoke, which could be changing the way their genes are regulated," Murphy said in a statement.
"The center is seeking to substantially improve our overall understanding of the environment's role -- including exposure to tobacco smoke -- in ADHD."
Genetic factors account for approximately 76 percent of the risk for ADHD, but the remaining risk is attributed to the environment, Murphy said.
Prior research showed tobacco smoke exposure causes epigenetic changes -- genes are changed -- but a comprehensive understanding of its effects and how it relates to ADHD risk is largely unknown, Murphy said.