Medical researchers have been puzzling for years over the effect alcohol consumption has on health. Many studies have indicated that drinking some alcohol (in particular, red wine) may provide benefits to the heart and circulatory system.

However, other studies have pointed to alcohol as a factor in the development of some cancers. Breast cancer risk seems to be related to alcohol consumption, but how much and what kind of alcohol affects that risk is still an unknown.

Doctor Yan Li, from the Kaiser Permanente health system in California, says she may have some more definitive answers. She and her colleagues reviewed health records of more than 70,000 women from a variety of ethnic backgrounds who entered the health system between 1978 and 1985. They gave the women questionnaires about their health habits then, and continued to query them periodically over the next two decades.

Studying the frequency of the women's drinking, they asked "whether they drank one to two drinks per day versus more than three drinks per day," Dr. Li says. "We studied whether or not they have particular preference of wine or beer, or liquor. And also we studied the red wine drinkers versus white wine drinkers." And they looked at their risk of breast cancer.

The researchers found that alcohol did increase the risk of breast cancer in these women, and that the quantity consumed was directly related to the risk. In other words, among the women who drank heavily, a higher percentage were diagnosed with breast cancer.

"For women who drink between one to two alcohol drinks per day, this increased their risk of breast cancer by ten percent, compared with the light drinkers who were defined as women drinking less than one drink a day," explains Li. "And the risk of breast cancer increased by 30 percent in women who drink more than three drinks per day."

About 4 percent of the women consumed more than 3 drinks a day. Li says that's comparable to the risk of smoking a pack of cigarettes a day. "I think that 30 percent is not really trivial," says Li. "If we put into population aspects, that 30 percent increase in the relative risk of breast cancer from heavy drinking might be translated into approximately about 3 to 5 percent of all women developing breast cancer as a result of their habits."

The researchers found that it made no difference whether women drank wine (red or white), beer, or liquor. It was the alcohol itself that raised the risk. Li says many other things increase a woman's breast cancer risk, primarily heredity and environment. But she says alcohol consumption is something that women can easily control.

She says her team's study is one of the largest to ever look at these risks and relationships between alcohol and cancer, and their findings were recently presented at the European Cancer Conference in Barcelona.