An experiment with students showed that volunteers exposed to a film and commercials where alcohol featured predominately drank an average one-and-a-half bottles of beer more during the hour they were watching.

The findings highlight a potential need to explicitly warn people – and parents – if movies contain alcohol use because such portrayals have a direct effect on drinking, researchers at Radboud University Nijmegen said.

"Implications of these findings may be that, if moderation of alcohol consumption in certain groups is strived for, it may be sensible to cut down on the portrayal of alcohol in programmes aimed at these groups and the commercials shown in between," Rutger Engels and colleagues wrote.

The study included 80 male university students who were shown two different films, one of which featured alcohol far less prominently. They were also shown either "neutral" commercials or ones with alcohol ads.

During the one-hour film in the laboratory fitted with leather couches and comfortable chairs, the students were also told they could drink as much beer and wine or soft drinks as they liked.

The most alcohol anyone drank was four bottles and the least amount was none, the researchers said, adding it was not possible to tell whether watching alcohol on screen has any effect on long-term behaviour.

"This is the first experimental study to show a direct effect of exposure to alcohol portrayals on TV on viewers' immediate drinking behaviour," Engels said in a statement.