Most studies indicate that there is a weak association between moderate alcohol consumption and the incidence of breast cancer, and that the risk of breast cancer increases as the level of alcohol consumption increases.

In a summary of 63 studies, 65% reported that alcohol consumption was associated with an increased risk of breast cancer.

Epidemiologic studies have suggested that alcohol consumption might increase breast cancer risk, and laboratory studies have shown that alcohol increases the amount of estrogen metabolites available in a woman's body, which can then act as a fuel for hormone-sensitive breast cancer.

The association is weak between alcohol consumption and breast cancer in women who drink one alcoholic beverage a day. Drinking 2 to 5 drinks per day may be associated with a rate of breast cancer that is about 40% higher than the rate for non-drinkers.

Some studies report that drinking before the age of 30 is more closely tied to breast cancer risk, and other studies report that current or recent drinking habits have a greater influence on breast cancer rates. Total amount of alcohol consumed during a lifetime regardless of the age at which the habit starts has also been suggested as an important factor when determining breast cancer risk.

Some studies report that consumption of beer and hard liquor has a greater association with breast cancer risk than the consumption of wine. Other studies report no difference in the type of alcoholic beverage consumed. Laboratory research has shown that resveratrol found in red wine suppresses the abnormal cell formation that leads to most types of breast cancer, suggesting a potential role in breast cancer prevention. The amount of resveratrol consumption needed for effective prevention might suggest supplemention  to be a more viable option than red wine consumption.

One of the largest studies of its kind has found that alcohol is a substantial risk factor for development of the ER+/PR+ (estrogen-receptor-positive and progesterone-receptor-positive) type of breast cancer. Researchers report that even moderate alcohol consumption, defined as one or two drinks per day, increased risk of developing this kind of cancer, and the more a woman drank, the higher her risk. Compared to women who did not drink at all, women who had three or more glasses of alcohol daily had as much as a 51 percent increased risk of ER+/PR+ breast cancer.
References:
1. Julie A. Napieralski, Carol Devine. Alcohol and the Risk of Breast Cancer. Program on Breast Cancer and Environmental Risk Factors in New York State.
2. Jasmine Q. Lew, et al. Alcohol consumption and risk of breast cancer in postmenopausal women. The NIH-AARP Diet and Health Study. American Association for Cancer Research.
3. Image by chik1117