"We don’t know why this is so. It may have to do with a parenting style that is permissive of activities that are not age-appropriate. Or it may be an outcome of all the smoking scenes in R-rated movies," said lead author of the study Chyke Doubeni, PhD, with the University of Massachusetts Medical School.

"But we do know that kids who believe it is easy to get a cigarette are at risk of smoking. Our prior research has already shown that kids who perceive cigarettes as readily accessible are more likely to end up as regular smokers," Doubeni added.

For the study, the researchers looked at data from the second Development and Assessment of Nicotine Dependence in Youth, a four-year study of 1246 sixth-grade students in Massachusetts who were interviewed 11 times from 2002 to 2006.

Students were asked if they agreed or disagreed with the statement: "It would be easy for me to get a cigarette." They were also asked "Is anybody allowed to smoke inside your home?" and "How often do your parents let you watch movies or videos that are rated R?"

The researchers found that parental permission to watch R-rated movies were one of the strongest predictors of the perception that cigarettes are available, about as strong as having friends that smoked.

If allowed to watch R-rated films, non-smokers were almost twice as likely, and smokers were almost three times as likely to say it would be easy for them to get cigarettes.