By 14 to 15 years old, U.S. girls are about 25 percent more likely to start drinking than are boys their age

Although tweens and teens should not drink alcohol, plenty do. So a major U.S. survey recently asked a large group of 12- to 24-year-olds how old they were when they had their first full alcoholic drink. Just a sip or two did not qualify, here. Girls, it now turns out, were more likely than boys to start drinking before age 18.

In fact, 14- to 15-year-old girls were about 25 percent more likely to drink than were boys their age.

That was a surprise. Other studies had shown adult men drink more, and more often, than do women. So most researchers had assumed this trend meant males were more likely than females to start drinking in their teens. The new study challenges that assumption.

The new study analyzed data from 400,000 young people. All had taken part in the National Survey on Drug Use and Health (NSDUH). That survey collects data from some 70,000 different Americans each year. It asks about their use of tobacco, alcohol, illegal drugs (including non-medical use of prescription drugs) and their mental health. The number of teens it includes is important. Asking a very large number of people the same question means their answers are likely to represent trends in the rest of the population.

Our study is the first to report at a national scale that adolescent girls are more likely to drink, says Hui Cheng. She works at Michigan State University in East Lansing. As an epidemiologist, Cheng investigates what causes a particular illness or bad habit and how to limit its spread. Her team’s new findings appeared April 3 in Alcoholism: Clinical and Experimental Research.

If more men than women drink, what explains girls starting to drink at a younger age than boys? The answer, Cheng’s data indicate, is that girls who start drinking early are more likely to stop drinking before the age of 21 than are those who start later. In contrast, boys who start drinking early continue to drink alcohol as adults.

But even if girls tend to stop drinking as they reach adulthood, that doesn’t mean their early behavior was harmless, says Cheng.

The brain doesn’t fully mature until people reach their mid-20s. Drinking alcohol, some research suggests, can interfere with the proper development of a teen’s brain. Last year, one study looked at this in a model of teens (young rats stood in for people). It found that alcohol can lead to long-lasting and harmful changes to a part of the brain called the hippocampus. This region controls memory and learning.

Scott Swartzwelder works at Duke University in Durham, N.C. An author of that study, he studies how brains function under the influence of alcohol and other drugs.

A teen’s brain is more sensitive to alcohols effects on memory and learning than is an adult’s. At the same time, adolescent brains are less sensitive to alcohols sedating effect. This effect can make someone sleepy.

Most adults have a few drinks and then say, OK, Ive had enough. Im going to bed, says Swartzwelder. Adolescents can drink a lot more before they feel sleepy,” he notes. “So they miss a primary signal to tell them theyve had enough.

And that may be why alcohol puts so many teens at risk. Although it is illegal for those under 21 to drink alcohol in the United States, this age group accounts for 11 percent of all alcohol consumed. Most of those drinks were consumed to excess, in a behavior known as binging.

Alcohol related injuries and other conditions send some 189,000 underage drinkers to U.S. emergency rooms each year. And some 4,300 U.S. deaths each year are linked to excessive underage drinking. These data come from the Centers for Disease Control and Prevention in Atlanta, Ga.

Most anti-drinking campaigns don’t target girls

Most programs to discourage teen drinking target boys, says Cheng. Yet if girls are more likely to start drinking when they are young, she says, that needs to change.

But first, she adds, researchers need to learn what encourages girls to start early. Chengs study did not try to answer that. But she suspects the answer could have something to do with changing attitudes towards alcohol.

Since the end of the Second World War in the mid-1940s, society has not judged women drinkers as harshly as it once did, Cheng says. This may have led to more girls, even at a young age, being exposed to alcohol.

The next step is to find out how much alcohol today’s girls are drinking: We are looking now at the transition to heavy drinking,” she says — from experimenting to potentially becoming an alcoholic.