New research links drinking, breast cancer

~ There are theories that alcohol changes women's estrogen metabolism.

Heavy drinking significantly increases the risk of developing breast cancer, and even moderate drinking -- just a glass or two of wine with dinner every night -- can make women more vulnerable to the disease, according to research by Kaiser Permanente doctors.

The study of more than 70,000 Kaiser patients, results of which were presented Wednesday at the European Cancer Conference in Spain, showed that women who drank three or more alcoholic beverages a day increased their risk of breast cancer by 30 percent. Women who drank one or two a day increased their risk by 10 percent.

Notably, it didn't matter what kind of alcohol the women drank, researchers said. That's an important distinction for wine drinkers, as research has shown that red wine might have some benefits, especially for cardiovascular health.

But moderate drinkers shouldn't necessarily stop having their daily glass of wine, the study's authors said. The risk of breast cancer is low enough that they'll want to take into consideration potential health benefits of drinking small amounts of alcohol.

Changing habits

Women who are heavy drinkers, however, or those who are already at high risk of developing breast cancer because of genetic factors, might want to reconsider their drinking habits, said Dr. Yan Li, co-author of the Kaiser study.

"Women should avoid heavy drinking, but in terms of light drinking, that depends on the patient's circumstances," Li said.

"A woman who drinks one glass of wine every night, whether she should keep doing that should depend on her own health, her family history," she said. "If a woman is relatively young and has a strong history of breast cancer or carries the gene for breast cancer, perhaps she should do everything she can in life to avoid factors that increase her risk."

Scientists don't yet know why alcohol affects breast cancer. Li said there are theories that alcohol changes women's estrogen metabolism, so that heavy drinkers end up with more estrogen in their bodies. Hormone-sensitive breast cancers can feed on estrogen.

In the Kaiser study, researchers looked at the self-reported drinking habits of 70,033 women who were interviewed during regular health exams in 1978 to 1985. By 2004, breast cancer had been diagnosed in 2,829 of the women.

Red wine included

The study is one of the largest to show that there is no distinction between different kinds of alcoholic beverages. It doesn't matter whether it's a 5-ounce glass of wine, a can of beer or a shot of liquor -- it's the alcohol that influences breast-cancer development.

"This study really conclusively and convincingly tells us that the source of the alcohol does not appear to make a difference," said Dr. Robert Carlson, an oncologist with the Stanford Cancer Center. "There has been some belief previously that red wine might not confer the same risk, and this shows that it does.

"The important thing is that most risk factors for breast cancer are not modifiable, and alcohol consumption is," he said.

Barbara Brenner, executive director of Breast Cancer Action in San Francisco, said it's important that women see these studies and understand the effect that drinking can have on their risk of breast cancer.

The group that saw the largest impact -- women who drink three or more alcoholic beverages a day -- might have bigger, more immediate problems than their long-term risk of developing cancer, Brenner said.

"By the time you drink enough to really increase your risk, your problem is alcoholism," she said. "Everyone else, if they're concerned, they might want to think carefully about how much they drink."