Stars who knock back whisky, wine or beer in a movie are an invisible but potent force in prompting youngsters to experiment with alcohol or binge-drink, a large US study published on Tuesday suggests.
Major exposure to scenes of alcohol consumption in movies is a bigger risk for teen drinking than having parents who drink or if booze is easily available at home, it says.
Unprecedented in its scope, the probe entailed a confidential telephone survey of more than 6,500 randomly-selected Americans aged 10 to 14 years, who were then interviewed three more times over the next two years.
The youngsters were surveyed on what big movies they had seen, whether they drank alcohol or owned merchandise with a liquor brand on it, and were also asked questions about their personality, school and home life.
The 50-movie list used in the interview was drawn randomly from 500 current or recent box-office hits plus another 32 films that had grossed at least 15 million dollars when the first survey was carried out.
The researchers then measured the amount of exposure to alcohol in movies, determined by a character's actual or implied consumption of a drink or purchase of it.
The youngsters, they found, had typically notched up a total of four and half hours of such exposure. Many had seen a total of more than eight hours.
During the two-year course of the study, the tally of respondents who said they had started to drink alcohol rose from 11 percent to 25 percent. The proportion who began binge drinking, defined as five or more drinks in a row, tripled from four percent to 13 percent.
Out of 20 risk factors for these two activities, the biggest by far was high use of alcohol among the youngster's peers.
But high movie alcohol exposure ranked the third biggest risk for the onset of drinking, and fourth in terms of progression to binge drinking.
It was a far greater risk than having dud parents or parents who drank, having lots of pocket money, being a rebellious character or having drink available at home.
"Movie alcohol exposure accounted for 28 percent of the alcohol onset and 20 percent of the bing drinking transitions," says the paper.
After confounding factors were taken into account, teens who watched the most movies featuring alcohol were twice as likely to start drinking as those who watched the least. They were also 63 percent likelier to progress to binge-boozing.
Why is this so?
"Alcohol use in movies is typically modelled in positive situations, without negative effects, and often shown with alcohol brands, which consolidates both the adolescent's identify as a drink and brand allegiance," the study suggests.
"Acquisition of alcohol-branded merchandise, an article of clothing with an alcohol brand on it, furthers this process."
The investigation is published in an online journal, BMJ Open.
Its authors, led by James Sargent, a professor at the Dartmouth Medical School in New Hampshire, say it is time to consider restrictions.
Sixty-one percent of Hollywood movies use product placement of some kind, they note. Producers cannot use tobacco in placements yet face no restrictions on alcohol.
Health watchdogs should be concerned, and not just in the United States, they warn.
More than half of Hollywood's revenues come from overseas distribution, mainly in Europe, Japan, Canada, Australia, Brazil and South Korea.
"Like influenza, images in Hollywood movies begin in one region of the world then spread globally, where they may affect drinking behaviours among adolescents everywhere they are distributed."