Breast cancer is one of the leading causes of cancer death in women around the world. In recent years, there's been some focus on what women can do to decrease their risk of breast cancer - such as breastfeeding and eating a good diet. One thing they've been urged not to do is drink alcohol. As Rose Hoban reports, there's now more evidence that that's good advice.

Researchers have found that alcohol intake affects specific types of breast cancer tumors more than others. Jasmine Lew, a researcher at the Howard Hughes Medical Institute, examined data from the NIH-AARP Diet and Health Study, a large study that's been collecting information on close to 200,000 women since 1995.

"They answered questions on this questionnaire that asked about the types of food that they were eating and the frequency that they were eating it as well as serving size," she explains. "So when it came to alcohol consumption, we asked them how much beer they were drinking during the summer and the rest of the year, how much wine they were drinking and how much liquor they were drinking. As well as each time when they drank how much they were drinking."

Researchers have found links between the amount of alcohol the women consumed and a higher risk of cancer. Lew and her colleagues found that alcohol increased the risk most for one particular class of breast cancer tumors: estrogen/progesterone receptor positive tumors. Lew says they are the most common types of breast cancer in postmenopausal women. "That is actually just one way in which we identify the different types of breast cancer. It's basically just a marker on the cell saying that there are receptors that are more responsive to estrogen, or more responsive to progesterone."

Both estrogen and progesterone are hormones produced by women. When women reach menopause, levels of these hormones in their bodies fall precipitously, which should lead to fewer of these tumors. But Lew and her colleagues found that post-menopausal women had higher rates of these hormone-responsive tumors if they drank alcohol. And the more they drank, the higher the risk. "So drinking as much as one serving of alcohol resulted in a 7% increase of risk for the estrogen/progesterone receptor positive types of breast cancer. And drinking as much as three servings of alcohol per day resulted in as high as 51% increase in risk."

Lew explains that drinking alcohol doesn't automatically mean a woman will develop cancer, but adding alcohol to her daily diet does increase the chances a woman will develop cancer at some point in her life.

Lew presented her research at the annual meeting of the American Academy of Cancer Research and will publish her findings later this year.