Women who drink up to seven glasses of wine or beer a week are slightly less likely to suffer a stroke than those who steer clear of alcohol, according to a U.S. study that covered thousands of women for nearly 30 years.

The results, published in the journal Stroke, fall in line with guidelines from the American Heart Association that recommend women have no more than one drink a day—but that doesn't mean people should take up drinking to stave off strokes, researchers said.

"We do not encourage women who do not currently drink to initiate drinking," said Monik Jimenez, a researcher at Brigham and Women's Hospital in Boston, who led the study.

"Alcohol is a double-edged sword, because higher levels can increase high blood pressure and atrial fibrillation, which are risk factors for stroke as well," she told Reuters Health.

Several previous reports have shown that low levels of alcohol drinking are tied to a smaller chance of having a stroke.

Jimenez and her colleagues used data from the massive Nurses' Health Study, which tracked the health, diet and lifestyle of more than 83,000 middle-aged women for 26 years.

They compared the drinking habits of women in the study who had had a stroke, to women who hadn't, dividing the women into five categories: from those who never drank, to the heaviest drinkers who had at least two and a half beers or two shots' worth of hard liquor or about three glasses of wine a day.

Of the roughly 25,000 women who never drank, about four percent had a stroke at some point during the study.

In contrast, two percent of the more than 29,000 women who had up to half a drink a day on average had a stroke. And of those downing between a half glass and a full glass daily, just one in 200 ended up suffering a stroke.

After the researchers took into account certain risk factors for stroke, such as smoking, being overweight and a history of heart disease, they found that having up to one drink a day was linked to a 17 to 21 percent lower chance of having a stroke.

The study didn't prove that alcohol prevented the strokes, and there's no known explanation for the relationship between the two.

It may have something to do with socioeconomic status, said Cheryl Bushnell of Wake Forest Baptist Medical Center, who was not involved in the study and noted that lower socioeconomic status is known to be linked with a higher risk of stroke and cardiovascular disease.

"My thought is that alcohol costs money. And I think that people who may be drinking light to moderate amounts with a meal are basically people who may have slightly higher means to buy that," Bushnell told Reuters Health.

"It's something that's a lifestyle."

But she did say that it's possible alcohol itself is responsible for the lower stroke risk. Jimenez suggested that alcohol might do so by preventing blood clots or altering cholesterol levels.

Her study did not show an increased risk of stroke among the women who drank the most, but other research has suggested that possibility. One found that having several drinks was actually linked to an increased risk of stroke in the next 24 hours.