Researchers analysed data from more than 5,200 primary school students in France and found that those exposed to secondhand smoke while in the womb and/or at a young age were at higher risk for behavioural problems, particularly emotional and conduct disorders and ADHD.
The association was strongest among children exposed to secondhand smoke both during pregnancy and after birth.
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However, because this was an observational study, the authors can't say for sure that secondhand smoke caused the behavioural problems.
The study was published online recently in the journal PLoS One.
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"Our data indicate that passive smoking, in addition to the well-known effects on health, should also be avoided because of the behavioural disorders it may cause in children," study leader Isabella Annesi-Maesano, research director at the French Institute of Health and Medical Research in Paris, said in an institute news release.
The results support animal research findings that nicotine in secondhand smoke may have a neurotoxic effect on the brain.
Those studies found that during pregnancy, exposure to nicotine smoke causes structural changes in the foetal brain, and that exposure to tobacco smoke during the first months of life causes a protein imbalance that affects the growth of neurons, the study authors said.
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