Teens who joke about killing brain cells while downing beers may find the idea a bit less funny when they grow up.
A report released yesterday by the American Medical Association shows that adolescents and young adults who drink may risk long-lasting brain damage, especially when it comes to learning, memory and critical thinking.
And in some cases it may take as little as a few beers to cause harm, according to the report, which synthesizes nearly two decades of research on alcohol and the brain.
Public health officials have long known that the number of young people who drink is on the upswing. In 2000, 3.1 million people age 17 and younger took a drink for the first time, according to the AMA report. Their average age: 12.
But scientists have only recently started to unravel the mystery of how alcohol affects the brain during youth. Now advances in neuroimaging and other technologies are providing provocative - and occasionally disturbing - clues.
One of the first lessons is that the brain appears to be particularly susceptible to damage during high school and college - the prime drinking years.
While the brain stops growing physically around the age of 5, its cells continue to refine and realign themselves until at least age 20. "We know that some of the most critical wiring doesn't even kick in until the second decade of life," says Scott Swartzwelder, a neuropsychologist at Duke University and the Department of Veterans Affairs.
Teen drinkers appear to be especially vulnerable to damage in two regions: the hippocampus, a structure deep in the brain responsible for memory and learning, and the prefrontal cortex, which is tucked just behind the forehead and involved in decision-making and reasoning.
For example, psychologist Michael De Bellis and colleagues at the University of Pittsburgh found that girls age 14 to 21 with serious drinking problems had 10 percent smaller hippocampi than did nondrinking peers.
The researchers, who used magnetic resonance imaging to peek deep into their subjects' gray matter, found that the girls who had been drinking longest had the smallest hippocampi.
But researchers are finding that it's not just heavy or binge drinking - officially defined as downing five or more drinks in quick succession - that can have negative consequences.
Duke researchers, for example, found that when they gave adolescent rats - often used as stand-ins for humans in alcohol research - the rat equivalent of just two drinks, the rodents had a tougher time remembering how to exit a maze than did sober animals. When the team repeated the study on a group of 21- to 24-year-old people, they found similar results: After three drinks, for a blood-alcohol level slightly under the 0.08 legal limit, volunteers were 25 percent less accurate on memory tests.
Swartzwelder, who was involved in both studies, says the brain appears to be most vulnerable to alcohol during the very ages when it's being tasked the most: the high school and college years. "It's exactly the wrong time to do the most heavy drinking," he says.
Other rat studies hint that heavy drinking during youth could have long-term consequences. Swartzwelder's colleague forced adolescent rats to imbibe the human equivalent of a 12-pack. They did this every other day for nearly three weeks and then stopped.
When these former binge-drinking rodents reached adulthood, they were found to be much less adept at memory mazes after a sip or two of alcohol than drunk adult rats who had never binged.
Despite growing evidence of alcohol's effect on the young brain, Swartzwelder and others caution that it's too early to reach definitive conclusions. For example, it's not completely clear whether alcohol causes a young person's hippocampus to shrivel - or whether an undersized hippocampus is more likely to cause heavy drinking.
Psychologist Sandra Brown, who also studies alcohol and the developing brain, says that everything from raging adolescent hormones to a subject's eating habits can make it difficult to prove conclusively that what scientists see in the lab is due to alcohol consumption. "It's subtle," notes Brown, who works at the Veterans Affairs Medical Center in San Diego. "The effects of alcohol build up over time."
She says ironclad proof will come only after scientists follow a large group of children from adolescence to adulthood, testing them all the way, a project on which she and her colleagues are now embarking.
While the biological picture is starting to come into focus, less clear is what to do about youth drinking.
The AMA, which compiled the report as part of an anti-drinking awareness campaign, argues that alcohol would have less of an effect on young brains if television networks curbed their youth-oriented alcohol ads.
The group is urging cable stations and television networks to stop airing alcohol ads before 10 p.m. or on programs with 15 percent or more underage viewers. They also want broadcasters to stop using cute cartoons and characters, such as Budweiser bullfrogs.
Pressure from the AMA and other anti-drinking advocates is thought to have contributed to NBC's decision in March to back away from a plan to run hard-liquor ads.