Breathing second-hand smoke could increase a child's risk of mental and behavioural disorders, including attention-deficit/hyperactivity disorder (ADHD), suggests a new study.
The study adds to evidence suggesting that kids of mothers who smoked while pregnant may be more likely to have behavioural problems. Second-hand smoke exposure has also been linked to heart and breathing problems in kids.
"It's time for us to begin to prevent children's exposure to (second-hand smoke) if we are serious about preventing these diseases," Dr Bruce Lanphear, who heads the Cincinnati Children's Environmental Health Centre said.
"We have sufficient evidence to prevent many of these diseases, but we don't," added Lanphear, who was not involved in the study.
Second-hand smoke and mental health
The authors, led by Frank Bandiera of the University of Miami Miller School of Medicine, studied the link between second-hand smoke and mental health in a nationally representative sample of almost 3,000 kids ages eight to 15.
Researchers measured the level of cotinine - which forms when nicotine in tobacco breaks down - in each kid's blood to find which kids had been exposed to second-hand smoke. Kids with the highest levels of cotinine were considered to be smokers themselves, and were not included in the study.
The researchers also interviewed all kids to see which ones showed symptoms of a mental or behavioural disorder.
After taking into account factors such as age and race, boys who were exposed to second-hand smoke were more likely to show symptoms of ADHD, depression, anxiety, and conduct disorder than those with no second-hand smoke exposure. Girls who were exposed to second-hand smoke had more symptoms of ADHD and anxiety only.
However, the number of kids actually diagnosed with most of the conditions was still small. While 201 kids, or about 7%, had enough symptoms of ADHD to be diagnosed with the disorder, only 15 kids were diagnosed with depression and nine with an anxiety disorder.
Researchers acknowledge that it can be difficult to separate the effects of second-hand smoke from harm caused by mothers smoking while those children were in the womb.
In a commentary accompanying the study, Dr Jonathan Samet from the Keck School of Medicine of the University of Southern California said that more research is needed to determine how exactly exposure to second-hand smoke could affect kids' brains.
Bandiera also noted that the study can't prove that second-hand smoke causes mental and behavioural disorders. But in the meantime, he said, "We should keep the kids away from second-hand smoke."
His study was published online in the Archives of Paediatrics & Adolescent Medicine alongside research from UK authors also showing a link between second-hand smoke exposure and poor mental health in about 900 kids.
The US Surgeon General has estimated that about 60% of children are exposed to second-hand smoke.
Lanphear said that while there might not be enough definitive evidence to tie second-hand smoke exposure to mental health problems, it would be a "surprise" if there was not a link between the two.
The authors conclude that more efforts are needed both to ban smoking in all public places where there are children and to prevent kids from being exposed to second-hand smoke at home.(Reuters Health/ March 2011)