Second-hand smoke causes negative behaviour
Children exposed to second-hand smoke are more likely to have learning and behavioural problems.
Of more than 55,000 U.S. children younger than 12 years, 6% lived with a smoker - and those children were more likely to have ADHD compared to children in smoke-free homes, the study, published in Paediatrics, found.

Even after accounting for a number of possible explanations, such as parents' income and education levels, second-hand smoke was still tied to a higher risk of behavioural problems, said Hillel Alpert at the Harvard School of Public Health, one of the researchers.

The findings don't prove a smoke-filled home is to blame, because there are other factors that the study didn't look at that may also be to blame - but it may give parents yet another reason to keep their homes smoke-free.

Health experts already recommend that children be shielded from second-hand smoke for health reasons, since it can increase their risk of respiratory infections, severe asthma and sudden infant death syndrome.

"The key message for parents is to protect their children from exposure to second-hand smoke," Alpert told Reuters Health.

One other factor to consider is that children exposed to second-hand smoke often had intra-uterine exposure as well, which has been linked to increased risks of learning and behavioural problems.

The results are based on a 2007 national survey of parents of 55,358 children younger than 12. The finding that 6% lived with a smoker translates into nearly 5 million U.S. children exposed to second-hand smoke at home, according to the research team.

About 20 percent of parents in smoking households said their child had at least one type of conduct disorder, versus less than 9% of parents in non-smoking homes.

The researchers said that it's unclear exactly how second-hand smoke would contribute to learning and behavioural problems. Some research has speculated that the smoke may affect certain chemicals in children's developing brains.

A second study in Paediatrics suggested that children's reactions to their parents' second-hand smoke may also play some role in their own likelihood of taking up the habit.

Among 165 low-income pre-teens from smoking households, those who thought second-hand smoke was "unpleasant or gross" were 78% less likely than other children to be at a high risk of smoking.

Alpert said that whatever the reasons for the current findings, they underscore the need for children to be kept away from smoke.

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