ATLANTA – College-age drinkers average nine drinks when they get drunk, government health officials said Tuesday. That surprising statistic is part of a new report highlighting the dangers of binge drinking, which usually means four to five drinks at a time.

Overall, about 1 in 6 U.S. adults surveyed said they’d binged on alcohol at least once in the previous month, but it was more than 1 in 4 for those ages 18 to 34.

And that’s likely an underestimate: Alcohol sales figures suggest people are buying a lot more alcohol than they say they are consuming. Health officials estimate that about half of the beer, wine and liquor consumed in the U.S. by adults each year is downed during binge drinking.

“I know this sounds astounding, but I think the numbers we’re reporting are really an underestimate,” said Dr. Robert Brewer, who leads the alcohol program at the Centers for Disease Control and Prevention.

The CDC report is based on telephone surveys last year of more than 450,000 adults. They were asked about their alcohol drinking in the past month, including the largest number of drinks they had at one time.

Binge drinking is generally defined as four drinks for women and five for men in a period of a few hours. Binge drinkers ages 18 to 24 reported nine drinks. The national average was eight.

But those numbers are likely averages for all episodes of binge drinking, Brewer said, citing other studies.