The study's findings show that teens are exposed to more alcohol advertisements than would be expected, influencing underage drinking.

Commercials for beer, wine and spirits tend to pop up more frequently on TV when teens are watching, a new study finds.

The study tracked 600,000 national cable ads in the U.S. between 2001 and 2006. It found that when more youth aged 12 to 20 were watching, alcohol ads increased.

For every one percentage point increase in teen viewership, there was a seven per cent increase in beer commercials, a 16 per cent jump in ads for spirits and a 22 per cent rise in ads for alcohol refreshers — drinks that contain alcohol but are heavily flavoured to taste like juice or pop.

At the same time, researchers discovered that when teens were watching, wine advertisements dropped by eight per cent, suggesting that marketers have the ability to pull ads during these viewing sessions.

"This study did not examine whether alcohol advertisers are intentionally overexposing adolescents," said lead study author Dr. Paul Chung, assistant professor of pediatrics at Mattel Children's Hospital UCLA, in a release.

He said the findings show that teens are exposed to more alcohol advertisements than would be expected, influencing underage drinking.

"The alcohol industry has consistently denied actively targeting teens, and our study isn't designed to test that claim. However, the ultimate effect of their advertising strategies, intentional or not, appears to be greater exposure than might be expected if adults were the sole targets of ads."

But David Hernigan, director of the Center on Alcohol Marketing and Youth and an associate professor at the Johns Hopkins Bloomberg School of Public Health, said in a release that despite marketers' pledges to avoid showing ads to audiences that have over 30 per cent underage viewers, that's not happening.

"This research suggests that ads are aimed at groups that include a disproportionate number of teens and that the alcohol industry's voluntary self-monitoring is not working to reduce adolescent exposure to ads," he said.

The study is to be published in the October issue of the American Journal of Public Health. It is now available online.