MONDAY, May 22, 2017 (HealthDay News) -- American teens are hitting the bottle less often than they did 25 years ago, new research reveals.

The analysis found that while 5 percent of 13-year-olds frequently binge drank between 1991 and 1998, only 2.6 percent were doing so in 2015.

Among 18-year-olds, that number fell from 20 percent to less than 15 percent in the same time frame.

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"Frequent binge drinking" was defined as knocking back five or more drinks in a row, on two or more separate occasions, over the span of two weeks.

And while rates are down overall, study author Joy Bohyun Jang said the trend isn't benefiting all teens equally.

"First," she said, "black youth have experienced slower declines since 1991. Second, the gender gap is narrowing recently due to female's slower decline in the frequent binge drinking rates. Third, the socioeconomic status gap is growing, due to slower decline among adolescents from lower socioeconomic backgrounds."

Still, the overall decline in binge drinkng means that "national and state-level programs targeted at underage drinking may have been effective," Jang said.

She's a postdoctoral researcher with the Institute for Social Research at the University of Michigan.

Her team's study was funded by the U.S. National Institute on Drug Abuse and the U.S. National Institute on Alcohol Abuse and Alcoholism. It will be published online May 22 in the journal Pediatrics.

The researchers noted that teens who engage in frequent binge drinking tend to be at higher risk for injury, risky sexual behavior, worse grades, and long-term drug and alcohol abuse.

The analysis relied on data on 8th-, 10th- and 12th-grader drinking habits that had been collected in a national study that surveyed more than 1 million youths between 1991 and 2015.

The biggest decline in frequent binge drinking was found among those born between 1985 and 1990.

As to what exactly is driving the trend, Jang suggested that "there's no clear answer."

But the team highlighted a number of positive factors that may have contributed, including increased public health efforts to raise awareness about the risks involved and a growing disapproval of binge drinking among youthful peers.

The rise of social networking as a means for meeting people may also have reduced the allure of drinking as a socializing mechanism, the investigators added.

On the downside, however, the team also theorized that some youth may simply be turning to drugs as an alternative to drinking.

Regardless, study co-author Megan Patrick pointed to a number of ways the trend could be improved even further going forward.

"Our results," she said, "suggest that more attention should be paid to those who are experiencing slower declines in frequent binge drinking," such as blacks, girls, and the poor.

Patrick is a research associate professor also at Michigan's Institute for Social Research.

Dr. Justine Welsh wrote an editorial that accompanied the study. She characterized the overall drop in frequent teen binge drinking as "substantial." Welsh directs the Emory Adolescent Substance Abuse Treatment Services at Emory University in Atlanta.

But she pointed to the racial and economic "disaparities" found in the study.

The problem, said Welsh, is that it's difficult to know what's behind the differences. "There are likely many factors," she said.

More information

There's more information on binge drinking at the U.S. Centers for Disease Control and Prevention.