Researchers from Harvard Medical School and Brigham and Women's Hospital followed more than 100,000 nurses in the Nurses Health Study, beginning in 1976. They assessed the women's alcohol consumption eight times from 1980 to 2008. During that time, 14 percent of the women were diagnosed with breast cancer.
Women who drank 3 to 6 alcoholic drinks per week had a 15 percent higher risk of breast cancer. In addition, women who consumed at least 2 drinks per day had a 51 percent increased risk of breast cancer compared to women who never drank alcohol.
Binge drinking, but not the frequency of drinking, was also associated with breast cancer risk. According to Dr. Wendy Chen of Brigham and Women's Hospital, "we looked at regularity of drinking which means how many days per week did someone drink and we found that after we controlled for how much they drank, it really made no difference how many days per week they consumed alcohol."
Researchers say they're not advising that women stop drinking alcohol because it may help prevent heart problems, but say the use of alcohol will need to be balanced against any risk of breast cancer. In the study, two or fewer alcoholic drinks per week were not associated with an increase in breast cancer risk.