Parents should quit smoking while their children are young to help prevent them from picking up the habit later on, according to a new study.
"Our analysis showed that the longer adolescents are exposed to a parent's smoking when the parent is addicted to nicotine, the more likely they are to begin smoking and to become regular smokers in the future," said lead author Darren Mays.
Quitting is of course important for parents' health, and could be important for kids' health too, said Mays, a public health researcher with the Cancer Prevention & Control Programme at the Lombardi Comprehensive Cancer Centre of Georgetown University Medical Centre in Washington, DC.
Read: Quitting smoking improves personality
"Our results suggest that for parents who are addicted smokers (quitting) may also reduce the likelihood that their children will go on to become smokers in the future," he told Reuters Health.
For the study, Mays and his colleagues followed 400 teens from early to late adolescence. Researchers separately interviewed the kids, most around age 14, and one of their parents, about their respective smoking histories.
The kids were interviewed again one year later and again four years after that.
6% of the kids were already regular smokers when the study began. 30% of the kids reported at all three interviews that they had never smoked.
The rest of the kids either experimented with a few cigarettes early on – nearly half of whom became regular smokers by year five – or experimented later on.
Teens whose parents were current smokers and addicted to nicotine were 10 times more likely to themselves become regular smokers at an early age or to experiment early on with cigarettes than kids with non-smoking parents.
Among the parents who were current smokers, each year they had smoked slightly increased the odds that their kids would end up in a heavy-smoking trajectory.
The results don't prove that parents smoking caused their kids to take up the habit, the study team acknowledges.
Evidence for both nicotine and alcohol
But there's no real debate about whether there is a link between parental and child smoking – researchers are confident that they are connected, probably due to a combination of genetics and social norms in the household, the researchers note in their report, published in Paediatrics.
Of the 24 kids who were already regular smokers at age 14, two-thirds had a parent who was a current smoker, compared to 3 with a parent that was a former smoker and 5 with non-smoking parents.
"There is strong evidence of this relationship for both tobacco and alcohol," said Mike Vuolo, associate director of the Centre for Research on Young People's Health at Purdue University in West Lafayette, Indiana. He was not involved in the new study.
This new research focuses specifically on nicotine dependence, which is "substantively important", Vuolo told Reuters Health by email.
"There is solid evidence that genetics explains the link between parent smoking and child smoking," said Jonathan Bricker of the Fred Hutchinson Cancer Research Centre in Seattle, Washington.
Read: Smokers will quit for their pets
"But what makes this study and others like it so important is that it identifies something practical and important we can do right now: help parents quit smoking for the sake of their children," Bricker told Reuters Health by email.
High risk of smoking
It might be a good idea to target quit-smoking initiatives at parents who are hooked on nicotine, not just those who smoke, he added.
But in terms of nicotine dependence, the new study contradicts previous research by the same team on the same subject, according to Denise B. Kandel, a professor of sociomedical sciences at Columbia University Mailman School of Public Health in New York.
"The earlier analysis found that onset of smoking was the same whether or not parents were dependent on nicotine," Kandel told Reuters Health by email.
By that logic, whether or not parents smoke at all is the important measure, not their dependence on nicotine.
The results are still important for public health advocates, who can identify children at high risk of smoking by whether or not their parents smoke, she said.
"The best advice for any parent who smokes is to quit as soon as possible and that resources such as their family doctor, telephone quit lines and online programmes are available to help," Mays said.
Women smokers at more risk
6 findings on SA smokers
Smokers' cars loaded with nicotine