If you’re a man, having one alcoholic drink is probably good for your health. If you’re a woman, the impact of that glass of alcohol is far more confusing.

Overall, science shows that for both men and women, drinking a small amount of alcohol each day is better for you than never drinking at all, and it likely lowers your risk of heart attack, diabetes and mental decline. But for women, moderate alcohol consumption also carries risks you may not know about.

Even small amounts of alcohol consumption are linked with higher risk for breast cancer. Women who drive after drinking are at higher risk than men of dying in a car accident, even at similar blood-alcohol concentrations. And women are at higher risk than men for serious health problems related to alcohol abuse, including liver, brain and heart damage.

The reasons alcohol appears to effect men and women so differently are complex. Women achieve higher concentrations of alcohol in the blood and become more impaired than men after drinking equivalent amounts of alcohol, even when taking into account differences in height and weight. This is likely due to the fact that a woman’s stomach empties more slowly than a man’s, giving the body more time to absorb the same amount of alcohol, many doctors say.

Lab studies suggest there may be gender differences in how alcohol affects the response to visual cues and other tasks related to driving performance, which may explain why it’s more risky for a woman to drink and drive. And alcohol also may alter a woman’s natural estrogen levels, which can influence her risk for a number of health concerns.

ONE OF THE MOST TROUBLING effects of alcohol is that even small amounts increase a woman’s risk for breast cancer. A pooled analysis by Harvard researchers of all the data on alcohol and breast cancer shows that a woman’s risk increases by about 9 percent for every 10 grams of alcohol a day that she drinks. In the U.S., the typical serving of 12 ounces of beer, 5 ounces of wine or 1.5 ounces of liquor delivers about 12 grams to 14 grams of alcohol, according to the Harvard School of Public Health.

That means a woman who consumes just two drinks a day has about a 27 percent higher risk of getting breast cancer than a woman who doesn’t drink alcohol.

It’s worth noting that the absolute risk of alcohol consumption to an individual woman is slight. Consider that the typical 50-year-old woman has a five-year breast-cancer risk of about 2.1 percent — so two drinks a day would boost her risk to only about 2.7 percent.

“It’s not a huge difference to an individual woman, but it could translate into many thousands of breast cancers in a year that would not have otherwise occurred,” says Walter Willett, epidemiology and nutrition professor at the Harvard School for Public Health. The alcohol-health equation “is definitely more complicated in women because of the relationship with breast cancer,” says Willett.

Exactly why alcohol consumption alters a woman’s breast-cancer risk isn’t entirely clear. Several studies have shown that alcohol can raise a woman’s natural estrogen levels, and high natural estrogen is linked with higher breast-cancer risk. Alcohol may enhance the negative effects of natural estrogen on the breast.

WHILE THE BREAST-CANCER RISK sounds scary, it has to be weighed against other health benefits of alcohol. Women who consume about one drink a day have a 40 percent lower risk for heart attack, and a 70 percent lower risk of stroke. In the well-known Nurses Health Study, which now follows more than 120,000 women, those with diabetes who drank at least a half-serving of alcohol a day had a 52 percent lower risk for heart attack than nondrinkers.

Studies also show that moderate alcohol use might protect against osteoporosis. Women who drink six to seven servings of alcohol a week typically have higher bone density than nondrinkers. The higher bone density is likely explained by the estrogen-enhancing effects of alcohol, doctors say.

As a result, women need to take into account family history and personal concerns. A woman with a strong family history of breast cancer or someone with a family history of alcoholism might decide to forgo alcohol altogether. But someone without those added risk factors who is worried about heart attack, diabetes or osteoporosis might consider drinking small amounts of alcohol daily.