Women who grew up when you could legally drink at 18 remain at higher risk of homicide and suicide well into their adult years, making a new argument for keeping the limit at 21, researchers said today.

The legal drinking age has been a moving target in the United States for nearly 80 years, since the lifting of a constitutional ban on alcohol during the Prohibition Era, 1920-1933. Fluctuations in the drinking age, between 18 and 21, where it currently stands, have created a “natural experiment” into the effects of permissive and restrictive policies on the brains and behavior of young people, according to Richard A. Grucza, an epidemiologist and assistant professor of psychiatry at Washington University School of Medicine in St. Louis, and his colleagues.

Grucza and his team wanted to investigate the longer-term effects of the lower drinking age on suicide and homicide after they observed more alcohol and drug problems among men and women from states that permitted alcohol sales to those younger than 21. Other researchers had found higher rates of drunk driving, homicide and suicide in states that permitted under-21 drinking, and toxicology studies have shown that drinking–and excessive drinking–play roles in suicide and homicide.

So, they dug into federal death records, census records and the Census Bureau’s American Community Survey, and came up with more than 200,000 suicides and 130,000 homicides among men and women who turned 18 between 1967 and 1989. Those were years in which the drinking age was in frequent flux.

Surprisingly, they found a higher risk of suicide and homicide persisting into adulthood only among women born after 1960 who came from states that permitted under-21 drinking, according to results released online today in the journal “Alcoholism: Clinical & Experimental Research.”  Women had a 12 percent higher risk of suicide and a 15 percent higher risk of homicide if they grew up where drinking was permitted at younger ages. Study authors could only speculate about why the effect applied solely to women.

“We can’t be sure why we see this effect in women, but not men,” Grucza told ABCNews.com. “But both suicide and homicide are very different phenomenon in women versus men.  For example, women who die by homicide are usually victims of somebody they know [e.g., domestic violence], whereas this is not the case for men.”

Suicide statistics bear out the notion that women attempt suicide more often than men, but men succeed in killing themselves more often than women. However, Grucza said, “alcohol results in suicide attempts being more lethal, so we suspect that long-term alcohol problems may lead to more frequently lethal suicide attempts among women.”

Using 2007 estimates of 3,600 suicides and 2,700 homicides among women born after 1960, Grucza and his co-authors calculated that a national drinking age of 21 “may be preventing about 600 suicides and 600 homicides annually.”

“Grucza and colleagues have elegantly demostrated that individuals who were young adults during a time in which they could legally drink between the ages of 18 and 21 have far-reaching health consequences into adulthood,” Katherine M. Keyes, a postdoctoral fellow in epidemiology at Columbia University who was not involved in the study, said in a statement released by the journal.

At the end of Prohibition, most states adopted a drinking age of 21. However, in the 1960s and 1970s, states decided that if young men could be drafted to fight in Viet Nam at 18 and citizens could vote at 18, then 18-year-olds should be allowed to make their own choices about alcohol. A subsequent rise in drunk driving deaths in the late 1970s caused a backlash, prompting states to restore the drinking age to 21. In 1984, a federal act made that the national standard.

However, in 2008, in response to continued underage drinking and binge drinking on college campuses, as well as support for letting adults make their own choices, college presidents and university chancellors launched the Amethyst Initiative to lower the drinking limit to 18 once more. The initiative also asks “elected officials to weigh all the consequences of current alcohol policies and to invite new ideas on how best to prepare young adults to make responsible decisions about alcohol use,” according to the Amethyst Initiative website.

Grucza thinks this is a bad idea. He stands among those who believe that the brains and judgment of young adults 18 to 21 remain vulnerable to effects of alcohol. So does Keyes: “This study is an important reminder of the public-health effectiveness of controlling alcohol at the population level during a very critical time in development,” she said.