Research Examines Possible Link Between Second-Hand Smoke And Kids' Depression, Anxiety, ADHD

Children and teens who are exposed to second-hand smoke could be at greater risk of suffering from mental health disorders like depression, anxiety and ADHD, according to a new study that's among the first to closely examine the potential association between second-hand smoke and mental health.

Researchers writing in the Archives of Pediatrics and Adolescent Medicine, looked at nearly 3,000 children, aged 8 to 15. According to the U.S. Surgeon General, more than 60 percent of children between the ages of 3 and 11 are exposed to second-hand smoke.

Smoke exposure in the children (who were part of the National Health and Nutrition Examination Survey conducted from 2001 to 2004), was determined by looking at serum cotinine levels -- a marker used to show how much smoke has entered the body. The 3,000 participants were also screened for potential mental disorders using the National Institute of Mental Health's Diagnostic Interview Schedule for Children questionnaire, which diagnoses for conditions included in DSM IV.

Ultimately, researchers found that higher serum cotinine levels were linked to symptoms associated with major depressive disorder, generalized anxiety disorder, ADHD and conduct disorder, which the American Academy of Child and Adolescent Psychiatry defines as a group of chronic behavioral and emotional problems.

But as the Los Angeles Times points out, "none of those symptoms added up to a single diagnosis of a mental health disorder that could be linked with exposure to second-hand smoke in the children and teens in the study. "The study's authors themselves state that they were limited by their inability to control for psychiatric history, meaning, the fact that children with depressed mothers are more likely to have poor mental health.

Still, the research joins an increasing body of evidence showing how second-hand smoke negatively affects children's health. Last month, TIME reported that second-hand smoke exposure upped the risk of stillbirth in nonsmoking pregnant woman by 23 percent, and also increased the risk of congenital birth defects by 13 percent. The study's authors found that the most common source of second-hand smoke was the baby's father.