For the first time, researchers have shown that watching characters knock back a beer or quaff another alcoholic beverage in films, TV shows or advertisements can have an immediate effect on how much viewers imbibe themselves.

A study by researchers in the Netherlands and Canada found that young males who watched films and commercials that prominently featured alcohol drank twice as much beer or wine on average as those who saw movies and TV ads in which booze was less evident.

"I think that many people are not aware of the fact that if you're exposed to alcohol cues, or even smoking cues, in movies (and) on television that it might affect your behaviour immediately," said principal investigator Rutger Engels, a professor of developmental psychopathology at Radboud University, in the Dutch city of Nijmegen.

The study involved 80 male university students, aged 18 to 29, who were randomly assigned to one of four groups. Participants watched films and commercials in a comfortable "home cinema" set up in a laboratory, with access to a fridge containing alcoholic and non-alcoholic drinks.

One group of 20 watched the film "American Pie," in which characters downed alcoholic drinks 18 times and booze was displayed another 23 times; a commercial break included alcohol ads. A second group viewed "American Pie" plus a commercial break with no alcohol ads.

The third group watched the film "40 Days and 40 Nights," in which alcohol was consumed three times and alcoholic beverages were shown 15 times. The commercial break included booze ads. The final group saw the same movie, but their commercial break had no plugs for intoxicants.

Over a one-hour period, students exposed to alcohol in both the film and commercials polished off an average of nearly three 200-millilitre bottles of alcohol, while those who watched "non-alcoholic" films and ads consumed 1.5 bottles on average.

"It was twice as much," Engels said in an interview Tuesday from Nijmegen.

The researchers, whose paper is published online Wednesday in the journal Alcohol and Alcoholism, speculate there are two reasons why seeing people drinking on the big or small screen prompts viewers to do the same.

Engels said the sight may act as an "alcohol cue" that creates a craving for booze in people who already drink.

"And if you constantly see people drinking …on the screen, you get thirsty — and not thirsty in the sense that you want a soda. You want a beer or a glass of wine," he said.

"This might imply that, for example, while watching an ad for a particular brand of beer, you are not only more prone to buy that brand next time you are in the supermarket, but also that you might go immediately to the fridge to take a beer."

People might also get an urge to grab a cold one or some other form of hooch because humans tend to imitate what others around them are doing, said Engels. "If you see actors constantly drinking alcohol, you also have the same response. If you sip more, of course, then at the end you drink more."

Robert Mann, a senior scientist at the Centre for Addiction and Mental Health in Toronto, said the study is the first to provide clear evidence of a causal relationship between viewing depictions of alcohol consumption and alcohol ads and subsequent alcohol consumption, at least in young males.

"Certainly if you're concerned about potential health impacts of advertising, you need that kind of causal information to really think about what you might do to prevent any harmful effects of the advertising," said Mann, who was not involved in the study.

"So the study, I think, is very significant in providing some evidence that those links are there and perhaps we need to be concerned about them. On the other hand, it's one study and it's also going to be important for us to replicate these findings and see how generalizable they are."

Engels said his team has begun another set of studies to see if their findings hold true for females and older males. They will also test the effects of smoking as portrayed in film and on TV.

The study's findings could provide the first solid scientific ammunition to those calling for the curtailing or banning of depictions of drinking in film and TV shows and in ads for alcoholic beverages.

Connie Uetrecht, executive director of the Ontario Public Health Association, said her group would like to see reduced alcohol advertising and stricter broadcast guidelines governing the prevalence of drinking on TV and film.

In effect, alcohol consumption in movies and TV shows "is a form of advertising, actually," said Uetrecht. "… And it obviously prompts people to drink."

"That's the worry. It becomes the social norm, so it looks like it's an OK thing to do."

Because he favours artistic freedom, Engels is not calling for a ban on drinking alcohol or smoking in movies or television shows.

"I think we should inform parents about it," he said of the study, "that if parents let their kids watch all kinds of movies at home or in movie theatres, then it might have these kind of effects and it might affect their behaviour."

"If you're a parent and you have 12- or 13-year-old kids and you let them watch in the evening all kinds of movies with a lot of alcohol in (them), maybe you should not be surprised that a couple of years later, your kids start to drink more, maybe quicker than their peers who are not seeing these kind of movies so much."