Parental smoking significantly influences the likelihood that children will take up cigarettes, according to a new study that suggests that the effect is especially potent during a child's pre-teen years, Reuters reported Jan. 28.

The study by researchers at the Harvard School of Public Health looked at 559 boys and girls ages 12 to 17 and their families. Approximately 62 percent of the parents had smoked at some point in their lives, with 46 percent having been considered nicotine-dependent.

Over 27 percent of the adolescents in the study reported having smoked cigarettes; 7.2 percent of the 12-year-olds said they had smoked, while 61.3 percent of 17-year-olds did.

The study found that a mother's smoking had an equal effect on both sons and daughters, and that a father's smoking had a stronger effect on boys. The researchers concluded that the longer a parent smoked, the greater an adolescent's likelihood of starting smoking — but the risk diminished if the parents quit smoking.

“What was striking to us is that the effects were strongest at younger ages,” said Stephen Gilman, a co-author of the study. Children of smokers ages 12 or younger were about 3.6 times more likely to smoke than children of non-smokers; adolescents ages 13 and older when their parents smoked were about 1.7 times more likely to smoke.

The study appeared in the February 2009 issue of the journal Pediatrics.