Children are more likely to start smoking and drinking alcohol before they reach their teens if one of their parents is absent during early childhood, a new study has found.

While previous research suggests that an absent parent increases the risk of smoking and drinking during adolescence, until now, it has been unclear whether it increases these risks at an earlier age. UK researchers decided to look into this further.

They used data from an ongoing study which has been tracking the health of thousands of children since they were born between 2000 and 2002. The children were assessed at the age of nine months, three years, five years, seven years and 11 years.

At the age of 11, they were asked about smoking and drinking alcohol.

For the purpose of this study, parental absence was defined as the ‘loss' of a biological parent by the age of seven, as a result of death or relationship breakdown.

The researchers had full data on almost 11,000 children. Of these, at least one in four had experienced the loss of a parent by the age of seven.

The study found that children who had experienced the loss of a parent by the age of seven were more than twice as likely to have begun smoking by the age of 11, compared to their peers.

They were also 46% more likely to have started drinking alcohol by the age of 11.

Which parent was missing had no bearing on the findings, the researchers noted. Although, they did find that those whose parent had died were less likely to have consumed alcohol by the age of 11, however among those who did, they were more than 12 times as likely to get drunk, compared to children whose parents were absent for other reasons.

"Associations between parental absence and early smoking and alcohol consumption may operate through a range of mechanisms, such as reduced parental supervision, self-medication, and adoption of less healthy coping mechanisms," the researchers from University College London said.

Details of these findings are published in the journal, Archives of Disease in Childhood.