People who start drinking as teenagers may be more vulnerable to becoming alcohol-dependent, a new study suggests.

In a study that looked at drinking habits among Americans born between 1934 and 1983, researchers found that over time, women began drinking at increasingly younger ages. At the same time, their rate of alcohol dependence climbed.

In fact, the study found, much of the increase in alcohol dependence seemed to be explained by the fact that women were starting to drink at younger ages. A similar pattern - earlier drinking and more alcohol dependence over time - was seen among men; however, the changes were much more dramatic among women.

The findings do not prove that early drinking causes alcohol dependence, lead researcher Dr. Richard A. Grucza told Reuters Health.

“But what is does show is that early drinking does not simply reflect a genetic vulnerability to alcohol dependence,” explained Grucza, of Washington University School of Medicine in St. Louis.

Women’s average age at first alcohol use and their rate of alcohol dependence both shifted significantly in a matter of decades. “Genes don’t change in that amount of time,” Grucza said.

The findings, published in the journal Alcoholism: Clinical & Experimental Research, are based on data from nearly 40,000 men and women who responded to two large national surveys - one conducted between 1991 and 1992, the other between 2001 and 2002.

Grucza’s team found that women born between 1934 and 1943 began drinking at the age of 22, on average. That age gradually declined among women born after 1943; those born after 1963 typically started drinking when they were 17.

Meanwhile, while 9 percent of women born between 1934 and 1943 had been alcohol-dependent at some point in their lives, this was true of roughly 22 percent of women born after 1963.

The increase in early drinking over time seemed to explain much of the increase in women’s alcohol dependence, the study found. For example, relatively younger women who started drinking at age 18 were no more likely to develop an alcohol problem than were older women who started drinking at 18.

Instead, the upswing in the number of early drinkers seemed to put more women at risk of alcohol dependence over time.

As for why early drinking might contribute to alcohol dependence, animal research suggests that the adolescent brain responds differently to drugs than the adult brain does, Grucza said.

“And those effects may last into adulthood,” he added.

Grucza also pointed out that while the current findings were most significant regarding women, it’s probable that if early drinking increases the odds of alcohol dependence, it does so in men as well.

SOURCE: Alcoholism: Clinical & Experimental Research, August 2008.