Light to moderate alcohol drinkers have an increased risk of breast cancer compared to women who do not drink beer, wine or liquor, said a US study published on Tuesday.
Women who drink three to six glasses of alcohol per week have a 15 percent higher risk of getting breast cancer than women who do not drink, said the research led by Brigham and Women's Hospital and Harvard Medical School.
Women who drink on average two glasses daily of alcohol show a 51 percent higher risk of breast cancer, said the study published in the Journal of the American Medical Association.
Researchers followed 105,986 women who answered survey questions about their health and alcohol consumption from 1980 until 2008.
The higher breast cancer risk was seen whether the women drank early in life or whether they were drinking after age 40, suggesting that even stopping may not have an effect on lowering risk.
The findings also present a dilemma for women who may choose to drink small amounts of alcohol, such as red wine, for heart health.
"There are no data to provide assurance that giving up alcohol will reduce breast cancer risk," said an accompanying editorial by Steven Narod, a doctor at the Women's College Research Institute, Toronto.
"Women who abstain from all alcohol may find that a potential benefit of lower breast cancer risk is more than offset by the relinquished benefit of reduced cardiovascular mortality associated with an occasional glass of red wine," he wrote.
The study authors said that the reason for the boost in breast cancer risk remains unknown, but hypothesized that it could be due to the elevation of sex hormones circulating in a woman's system after she drinks alcohol.