The lead author of the report, which appeared in Pediatrics, said the conclusion supports the idea that the smoking itself - not the sex, profanity or violence that may go along with it in certain films - influences teens to take up the habit.
"Movie smoking seems to be just as impactful if it's packaged in a PG-13 movie as opposed to an R movie," said James Sargent, from the Geisei School of Medicine at Dartmouth in Lebanon, New Hampshire.
"I really think it's a 'cool' factor. The more they see it, the more they start to see ways that (smoking) might make them seem more movie star," he told Reuters Health.
Sargent and his colleagues counted how many times a character was seen smoking in each of over 500 box-office hits from recent years. Then they asked 6,500 U.S. children aged 10 to 14 which of a random selection of 50 of those movies they'd watched.
The average "dose" of movie smoking was 275 scenes from films rated PG-13 and 93 scenes from R movies, the researchers said.
In three subsequent interviews with the same youths, those who had watched smoking-heavy movies were more likely to pick up the habit themselves. For each extra 500 smoking shots reported in their initial survey, young people were 33 to 49 percent more likely to try cigarettes over the next two years.
The effect of on-screen smoking was not significantly different for PG-13 and R films. Because young people tend to see more PG-13 films, Sargent's team calculated that if smoking automatically earned an R rating, the number of youngsters who try cigarettes would drop by 18 percent.
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