Parental absence in early childhood as a result of death or relationship break-up is linked to an increased risk of children starting to smoke and to drink alcohol even before they reach teenage years, says a study.

"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 said.

The researchers from University College London drew on data from the UK Millennium Cohort Study, which has been tracking the health of almost 19,000 children born between 2000 and 2002, in regular surveys.

The first of these was carried out nine months after birth, with subsequent surveys when the children were three, five, seven and 11 years old.

At the age of 11 the children were also asked whether they had ever smoked or drunk alcohol, and whether they had ever consumed enough to feel drunk.

Parental absence was defined as the 'loss' of a biological parent before the child was seven years old.

In all, the researchers had complete data for almost 11,000 children, more than one in four of whom had experienced the 'loss' of a parent by the age of seven.

Analysis of the data showed that children who had experienced parental absence before the age of seven were more than twice as likely to have taken up smoking and 46 per cent more likely to have started drinking alcohol by the age of 11.

The findings were published online in the journal Archives of Disease in Childhood.