“A woman reaches a higher blood alcohol level than a man after drinking the same amount of alcohol, even if they’re the same height and weight,” says George Koob, director of the National Institute on Alcohol Abuse and Alcohol¬ism at the National Institutes of Health.

That’s mostly because women’s bodies contain less water, notes Koob. And less water means a higher concentration of alcohol in their blood and in their cells after drinking the same amount as men.

But the effect of alcohol is not just a matter of becoming impaired more easily. Women who drink regularly are at increased risk of breast cancer.

“Alcohol is related to both premenopausal and postmenopausal breast cancer,” says Walter Willett, chair of the Department of Nutrition at the Harvard T.H. Chan School of Public Health. “And the more you drink, the higher your risk.”

Drinking over more of your life also matters. “Women who started drinking earlier in life and then stopped, their risk goes down,” Willett explains. “The highest risk is in women who started consuming alcohol early and continued.”

And it’s not just heavy drinking

“We now see a 17 percent increased risk with only one drink every other day,” notes Willett. “What’s remarkable is how modest that amount is. With colorectal cancer, you don’t see much increase in risk until you get to over two drinks a day.”

Alcohol’s ability to raise blood estrogen levels appears to explain at least part of the increased risk. “But we’re still not entirely sure whether it’s limited to the increase in estrogen or whether there’s more to it than that,” adds Willett.

“Alcohol is also a stronger risk factor for estrogen-positive cancer than for estrogen-negative breast cancer,” says Regina Ziegler of the Division of Cancer Epidemiology & Genetics at the National Cancer Institute. Estrogen-positive breast cancers are more common in older women.

The American Cancer Society recommends that women limit alcoholic drinks to one a day, if they already consume alcohol.

Does it matter what kind of alcohol?

“It’s the alcohol content that matters,” says Koob. “We don’t see any difference among wine, beer, or distilled spirits in their health effects.”

Drinking can have more consequences for women in other ways.

“Females tend to suffer more toxicity associated with alcohol across the board,” says Koob. “It makes them more susceptible than males to alcohol-induced liver inflammation, cardiovascular disease, accidents, and sexual assault.”

Why are women’s livers more sensitive to alcohol? “Truthfully, we don’t know,” says Koob. “But it’s a high priority for research at the National Institutes of Health.”

David Schardt writes for NutritionAction.com, which is produced by the nonprofit Center for Science in the Public Interest and is loaded with practical tips for eating right, cooking healthful recipes, and avoiding food-safety dangers, as well as news of the latest developments in nutrition and health.