In addition to the numerous health problems associated with exposure to secondhand smoke — namely asthma, allergies and respiratory distress — a number of studies have been conducted over the years linking secondhand smoke to psychological distress in kids as well as poor grades. A study published in April found that kids exposed to secondhand smoke may suffer from depression, anxiety and ADHD. Now a new study has emerged making an even stronger link in these findings.  

For the study, researchers from the Harvard School of Public Health analyzed data for 55,000 children aged 11 and younger from a 2007 national health survey. They found that children who were exposed to secondhand smoke were twice as likely to develop learning disorders, ADHD, and behavior disorders than were children who lived in smoke-free homes.

According to Hillel Alpert, a senior research associate at Harvard and one of the study's authors, "274,000 cases of the most common neurobehavioral disorders could have been prevented with smoke-free homes." That's a strong statement and one that squarely places the onus of responsibility for cases of ADHD and other learning disabilities on the shoulders of parents and caregivers.

Alpert was quick to add that while his study did not find that secondhand smoke directly caused ADHD or learning disabilities, there is a "strong evidence of association" between secondhand smoke exposure and these disorders that might indicates a relationship and warrants further study.