Thomas E. Rohan, PhD, and colleagues from the University of Toronto, found women who drank more than 50 grams per day of alcohol ? an amount equal to about four or five beers ? were 1.7 times more likely to develop breast cancer. The study analyzed 1,336 women with breast cancer and compared them to 5,238 women without the disease. Findings were published recently in the journal Cancer Causes and Control (Vol. 11, No. 3).

Most significantly, "the risk we observed was with high levels of alcohol consumption, of the order of four drinks a day on average," says co-author Anthony B. Miller, PhD. "There was little indication of increased risk with more normal levels of consumption."

Previous studies conducted by the American Cancer Society (ACS), however, found averaging two or more drinks daily can significantly increase breast cancer risk as well as increase risk of several other cancers.

Dr. Miller says the research suggests women should limit their alcohol consumption to an average of not more than two drinks a day if at all. ACS data support the advice of limiting alcohol intake to an average of fewer than two drinks daily.

The new study was part of the Canadian National Breast Screening Study, a randomized trial of screening for breast cancer in women 40 to 59. The women completed lifestyle and dietary questionnaires to identify lifestyle factors that may affect breast cancer risk.

The authors also point out an increased risk was seen in all types of alcoholic drinks ? wine, beer and spirits ? which suggests breast cancer risk is related to alcohol consumption itself rather than to other substances in the beverages.

Heather Spencer Feigelson, PhD, Senior Epidemiologist for the ACS, says this study adds to the growing body of evidence that moderate alcohol consumption (2 or more drinks per day, on average) is linked to a modest increase in risk of breast cancer. "This study is consistent with the dozens of other studies that have looked at this question previously," she says.

The reason alcohol may increase the risk of breast cancer is not fully understood, according to Dr. Feigelson. It may be due to the role of alcohol in increasing plasma estrogen and insulin-like growth factor levels, which could increase cancer risk.

"Women at higher risk of breast cancer may want to consider limiting their use of alcohol," she says. "Alcohol consumption is one of the few breast cancer risk factors that can be easily modified."

Some of the factors that give women the highest risk for breast cancer are having a family history of the disease, beginning menstruation at an early age, undergoing menopause at a late age and having one?s first full-term pregnancy at a late age, Dr. Feigelson says. Increased physical activity, prolonged lactation and maintaining a low body mass index after menopause are linked to lower risk, she adds.

It is known that alcohol also increases the risk of cancers of the mouth, throat, esophagus and larynx, especially among people who smoke. It also contributes to liver cancer and other liver diseases, as well as accidents. Although moderate alcohol use reduces heart disease risk, other lifestyle factors such as exercise and a healthy diet lower risk of both heart disease and cancer.