Smoking on film has declined since 2005, but cigarettes are still featured in far too many films, according to a new report.
The common practice could influence young people to smoke and should be countered by warnings before such films, say the study's authors.
"The results of this analysis indicate that the number of tobacco incidents peaked in 2005, then declined by approximately half through 2009, representing the first time a decline of that duration and magnitude has been observed," the team at the U.S. Centers for Disease Control and Prevention, the University of California San Francisco and elsewhere wrote.
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"However, nearly half of popular movies still contained tobacco imagery in 2009, including 54 percent of those rated PG-13, and the number of incidents remained higher in 2009 than in 1998," they added in the CDC's weekly report on death and illness.
Congressmen Edward Markey and Joseph Pitts, who both serve on the Energy and Commerce Committee, wrote the Motion Picture Association of America encouraging the industry to adopt stronger anti-smoking measures.
"Exposure to onscreen smoking in movies increases the probability that youths will start smoking. Youths who are heavily exposed to onscreen smoking are approximately two to three times more likely to begin smoking than youths who are lightly exposed," the CDC report reads.
The researchers counted each time tobacco use was shown in the biggest-grossing films of 1991 to 2009.
"This analysis shows that the number of tobacco incidents increased steadily after the 1998 Master Settlement Agreement between the state attorneys general and the major cigarette companies, in which the companies agreed to end brand placement," they wrote.