As an emergency room doctor, I’ve long observed how gendered health and disease are. One classic example is a particular subpopulation that presents to emergency care with high frequency: the individual whose daily, heavy drinking means that it is rare to see them sober. For mysterious reasons, this population used to be overwhelmingly male. When I graduated from medical school, in fact, I had never met a woman who fit this description.

Over time, this has changed in my personal practice, and recent research suggests the gender imbalance in all alcohol-related ER visits is changing across the nation.

In a recent study in the journal Alcoholism: Clinical and Experimental Research, researchers looked at millions of emergency room visits nationally between 2006 and 2014. They showed that ER visits related to alcohol are increasing markedly—particularly in women. The trend brings women’s visits closer to those of men, who have had the dubious distinction of dominating in terms of prevalence of alcohol-related problems.

In my work studying substance use disorders and women’s health, I’ve been watching this gap close for many years across all types and metrics of risky drinking, including binge drinking, alcohol abuse, and physiologic dependence.

However, this study was especially concerning for a few reasons.

First is the magnitude of the change. In this national hospital sample, over nine years, the number of alcohol-related ER visits rose 61.6 percent—even though per capita alcohol consumption increased by less than 2 percent and total ER visits increased by just 8 percent during that time. Looking just at women, the total number of alcohol-related ER visits increased from 947,173 visits in 2006 to 1,609,320 visits in 2014; for men, the total of number of alcohol-related ER visits increased from 2,132,645 visits in 2006 to 3,366,477 visits in 2014.

The rates of alcohol-related ER visits increased in almost all age groups for both men and women, but the annual percentage increase was significantly larger for women (5.3 percent) than it was for men (4 percent). The steepest increase for women was seen in the 25-34 age group and the 55-64 age group. While the increase in acute alcohol-related ER visits was similar for both genders, the increase in chronic alcohol-related ER visits was significantly higher for women (6.9 percent) than for men (4.5 percent).

Aaron White, Ph.D., the study’s lead author, tells SELF that this was a surprise to his research team as well. “We suspected alcohol-related ER visits might be increasing more for women than men, but we had no idea the increases for women were so big.”

The types of visits were an additional surprise: Many of the additional visits were by young women who required medical attention for problems related to chronic drinking (i.e., long-term, heavy alcohol use), for example, alcohol withdrawal or alcohol-related liver damage or heart damage. “These are not the types of visits one expects to see among young women in this age range,” he said.

While the closing gap is not completely understood, there are hypotheses among certain specialists who deal with this in their careers.

One is that equality in the workplace has led to shifting social norms and greater exposure of women to the drivers of heavy alcohol use, such as career-related stress and workplace functions that virtually require the consumption of alcohol. In other words, women may have lost the relatively protective environment of being at home.

But White warns that it’s not just as simple as women acting socially more like men: “It is far more complicated than that,” he states. He points out data from the Monitoring the Future study (a longstanding national study of the attitudes and behaviors of 8th through 12th graders), which demonstrates that among high schoolers, a long-standing gender gap in alcohol use has disappeared because males declined faster than females, not because drinking by females increased.