Even as few as three alcoholic beverages per week may increase a woman's risk of developing breast cancer, a new study finds.
Women in the study who drank three to six glasses of wine per week were 15 percent more likely than those who did not drink to develop breast cancer, researchers found in reviewing data taken over a 28-year period.
The study adds to the growing body of evidence of a link between alcohol consumption and an increased risk of breast cancer. Drinking moderate to high amounts of alcohol has previously been linked with breast cancer risk, but the effects of consuming low amounts of alcohol had been unclear. Alcohol may be increasing breast cancer risk by altering levels of the sex hormone estrogen, the researchers said.
Still, while the increased risk found in this study is real, it is quite small. Women will need to weigh this slight increase in breast cancer risk with the beneficial effects alcohol is known to have on heart heath, said Dr. Wendy Chen, of Brigham and Women's Hospital in Boston. Any woman's decision will likely factor in her risk of either disease, Chen said.
Chen noted that women who consumed fewer than three drinks per week had no increase in breast cancer risk.
"I don't think the take home message would be that women can't drink at all," Chen said.
Alcohol and breast cancer
Chen and colleagues examined information from 105,986 women who were followed from 1980 to 2008 as part of the Nurses Health Study. Women periodically answered questionnaires about their alcohol consumption and whether they had been diagnosed with breast cancer.
During the study period, 7,690 cases of invasive breast cancer were diagnosed.
The study found a rate of 333 cases of breast cancer per 100,000 women among those who drank three to six glasses of wine per week. There were 281 cases per 100,000 for women who drank no alcohol.
For those who consumed more than six glasses a week, the risk was higher. For women who consumed at least two drinks a day, the rate was 413 cases per 100,000 women — a 51 percent increase in breast cancer risk.
The study will be published tomorrow (Nov. 2) in the Journal of the American Medical Association.
When to stop drinking
It's not clear whether women could benefit from ceasing to drink alcohol by a certain age, wrote Dr. Steven Narod in an editorial accompanying the study. For instance, if alcohol exerted effects similar to hormone therapy (a treatment known to increase breast cancer risk in post-menopausal women), then women over 50 might benefit from cessation, said Narod, of the Women's College Research Institute in Toronto.
For some women, it seems the increase in risk of breast cancer may be substantial enough that cessation would be prudent. However, there are no data showing that giving up alcohol will reduce breast cancer risk, Narod said.
And it's possible that, for some, the benefit of drinking alcohol for the heart outweighs the risks of breast cancer, Narod said. Future research into alcohol's risks and benefits may provide women with more information to make a decision, Narod said.
Pass it on: Drinking three to six glasses of alcohol per week slightly increases breast cancer risk in women, a study suggests.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.