Breathing in secondhand smoke may contribute to behavior problems in children.
A new Harvard study suggests kids who are exposed to secondhand smoke are 50-percent more likely to develop a neuro-behavioral disorder -- like ADHD.
Researchers used national survey data of about 55-thousand children for the study... and found about 6-percent of kids under age 12 were exposed to secondhand smoke.
The study does not prove smoking causes behavior problems -- it simply shows an association. Experts say more studies are needed.