American women have almost a one in eight lifetime risk for breast cancer. And drinking alcohol--especially at high levels--may increase that risk.

Last year the National Institute on Alcohol Abuse and Alcoholism (NIAAA) issued its Tenth Special Report to the U.S. Congress on Alcohol and Health. Included in it is a summary of current research on alcohol and breast cancer.

The report cites "substantial evidence" that "breast cancer risk is elevated for women consuming high levels of alcohol (more than three drinks per day) compared with abstainers." Even one or two drinks per day might raise the risk.

Possible links between alcohol and breast cancer were first noted in women who took part in the third National Cancer Survey (1977). Nearly 50 similar studies followed. Not all of them found a link between alcohol and breast cancer. But researchers gathered enough evidence for the link to sound a clear caution.

One meta-analysis (combining data from several of the studies) indicated that women who had three or more drinks per day had a 69 percent higher risk of breast cancer than nondrinkers. Another meta-analysis showed that women who had two to four drinks per day increased their breast cancer risk by 41 percent.

The studies did not distinguish between wine, beer or mixed drinks. None of these is "safer" than the others. In fact, standard servings of each beverage contain the same amount of alcohol (about 13 grams).

Researchers are not clear about exactly how drinking can promote breast cancer. But four possible clues have emerged:

• Alcohol may affect hormone levels, especially for estrogen. And higher lifetime levels of estrogen present a key risk factor for breast cancer. When women combine drinking with birth control pills or hormone replacement therapy, their estrogen levels can increase even more. In addition, some alcoholic beverages, including bourbon and whiskey, contain phyto-estrogens-chemicals that have effects similar to estrogen.
• Alcohol may alter breast tissue. When a woman's breasts contain more dense calcium deposits than normal, her chances of breast cancer increase. (These deposits typically show up in a mammogram.) Alcohol may impair the immune system's ability to prevent these deposits
• Women who drink heavily may have poor nutrition. Specifically, they may eat fewer fruits and vegetables-foods that contain cancer-preventing chemicals. In addition, alcohol may decrease the body's ability to use existing stores of vitamin C, beta-carotene, and lutein/zeaxanthin. Each is a nutrient that we commonly get from food.
• Though alcohol itself is not a carcinogen (a chemical that promotes tumor growth), alcohol may become a "co-carcinogen." In other words, alcohol can combine with other chemicals, such as those in cigarettes, to increase cancer risk.

The possible association between alcohol and cancer is not confined to breast cancer. A 1993 report from NIAAA cites research linking heavier drinking with cancer of the esophagus, mouth, larynx and colon.

"People should be cautious to limit their drinking throughout life," said Denise Russo, branch chief for biomedical research at NIAAA. "This is true especially for women at younger ages who are taking birth control pills and probably consuming alcohol."

Russo sides with the NIAAA's current suggestion that women consume no more than one alcoholic drink per day. In fact, she would like to see more women abstain completely from alcohol.

"Once women are aware of cancer risks, they might view their oral contraceptive use differently, along with their diet and alcohol consumption," said Russo. "And certainly if they are smoking, they should take that into consideration as well. It's so important to make people aware that alcohol can interact in the processes that create cancer."

--Published May 7, 2001