TUESDAY, Nov. 15 (HealthDay News) -- Entering adulthood in a place and time where the legal drinking age is 18, not 21, seems to put women, but not men, at a long-term higher risk for homicide and suicide, a new study finds.

"We want to make sure people know all of the consequences of the [legal] drinking age," said study lead author Richard Grucza, an assistant professor in the department of psychiatry at Washington University School of Medicine in St. Louis. "Because while the rationale for raising the age was to keep young people from drinking and driving, there wasn't a lot of thought about the long-term habit-formations that may be occurring when young people drink."

Grucza and his colleagues discuss their findings in the February issue of Alcoholism: Clinical & Experimental Research.

In the study, the researchers tracked the histories of Americans who came of age prior to the full implementation of a 1984 federal law establishing 21 as the national drinking age -- in other words, people who turned 18 sometime between 1967 and 1989. This was a period when the legal age for drinking still varied widely between states.

The authors noted that in the 1960s and 1970s, many states had lowered the minimum drinking age to 18, to reflect parity with eligibility for both the military draft and voting.

However, a subsequent rise in drunk-driving deaths drove many states to revert back to a drinking age of 21 -- a move later made universal by passage of the 1984 federal law.

In prior short-term analyses, Grucza's team had found that both men and women raised in under-21 states engaged in higher rates of alcohol and drug use as adults, and had a higher rate of drunk-driving accidents, homicides and suicides.

In the new study, the authors set out to gauge the longer-term impact of drinking age laws on homicide and suicide, examining data on about 200,000 suicides and 130,000 homicides that took place in the United States between 1990 and 2004.

Looking at residents of the 39 states where the drinking age was pushed upward to 21, the team found in 37 of those states that women who grew up being able to drink below the age of 21 had a 12 percent higher risk for suicide -- a trend that stretched far into adulthood -- than women who matured when the legal drinking age was set at 21.

And in 38 out of 39 states, women who had matured when the legal drinking age was below 21 had a 15 percent higher risk of dying from homicide, the study found.

These trends were not mirrored among men, however.

"As for the different findings concerning men and women, it's hard to say why that happened," Grucza said. "We can start by saying that it's well understood that suicide and homicide are very different phenomena for men and women, independent of drinking habits. And perhaps alcohol tips the dynamic. But at this point it's just speculation based on past literature. We don't have the specific data to ferret that out."

There are important gender differences when it comes to suicide and homicide, the researchers pointed out. For example, while women are known to attempt suicide more often than men, men are more apt to carry suicide to completion. So, drinking might raise the number of suicide attempts that end in completion for women, the researchers reasoned.

Female victims of homicide are most often killed by an acquaintance, often during episodes of alcohol-fueled domestic violence, Grucza's team noted. Allowing men to begin drinking at a younger age might up the odds of that happening over time, they added.

Regardless, Grucza and his associates concluded that raising the drinking age appears to have had a positive societal impact. They estimate that upward of 600 suicides and 600 homicides have been prevented each year simply by having 21 as the nation's drinking age.

One key to the trend may lie in alcohol's effects on the young brain.

"We suspected that adolescence is a unique period in terms of the brain's response to alcohol and the vulnerability for addiction," Grucza explained. "And, in fact, what we have here is a natural experiment that supports that idea, by demonstrating an unintended but positive consequence that comes from having raised the drinking age."

Dr. James Garbutt, a professor of psychiatry at the University of North Carolina at Chapel Hill, called the study "intriguing."

"We've known for some time that changes in the drinking age, initially brought about by efforts to limit drunk driving, has been one of the biggest public health successes in our lifetime," he noted. "But there's been this thought about reducing the drinking age again, because some say, 'College kids are drinking anyways, so why don't we make it legal?'"

"But this is an important finding that shows the evident value of maintaining the 21 drinking age," Garbutt added. "And it is a clear argument that doing so is probably good for public health on multiple levels."

More information

There's more on the minimum drinking age at the American Medical Asociation.