Children who are exposed to passive smoking may be more likely to become antisocial and physically aggressive later in life, a new study indicates.

According to Canadian researchers, 40% of the world's children are exposed to secondhand smoke and exposure during early childhood ‘is particularly dangerous as the child's brain is still developing'.

They analysed data relating to over 2,000 children who were monitored from birth until they were 10 years old. Parents provided information about exposure to passive smoking, while teachers and the children themselves provided information about behaviour in the classroom.

"Previous studies looking at groups of children have generally asked mothers whether they smoked or not, and how much at each follow-up, rather than asking whether someone smoked in the home where young children live and play," explained Dr Linda Pagani of the University of Montreal.

She also noted that ‘few studies have looked at antisocial behaviour in the parents and even fewer have investigated the subsequent influence of prolonged exposure to secondhand smoke over the long- term'.

The study found that children who had been exposed to passive smoking were more likely to become antisocial or physically aggressive adults. Furthermore, these results stood irrespective of whether they were exposed to smoke while in the womb or whether their parents had a history of being antisocial.

According to the scientists, passive smoking represents the ‘most preventable cause of disease and disability'.

"This study suggests that the postnatal period is important for the prevention of impaired neurobehavioral development and makes the case for the promotion of an unpolluted domestic environment for children," they added.

Details of these findings are available in the Journal of Epidemiology and Community Health.