As a woman's alcohol consumption increases, so apparently does her risk of contracting breast cancer, say the Harvard researchers who took the most comprehensive look yet at the link between the two.
Pooling results of 16 previous studies, Harvard School of Public Health researchers say they found "strong evidence" linking alcohol consumption to the disease that strikes about one out of 11 American women.The Harvard team reported Thursday that based upon its findings and the percentage of women who drink, "it can be calculated that 13 percent of all cases of breast cancer in the United States might be attributable to alcohol consumption."
Matthew Longnecker, who directed the survey, cautioned that the findings do not prove alcohol causes breast cancer. Currently, a family history of the disease is the biggest risk factor for developing it.
"There may be some factor that results in both a tendency to drink alcohol and a tendency to develop breast cancer," Longnecker and the other researchers wrote in Thursday's Journal of the American Medical Association.
The Harvard team examined both "case-control" studies, in which past drinking habits of women with breast cancer were compared with cancer-free controls, and follow-up studies, in which drinking habits of large groups of women were recorded and the women were tracked to see who developed cancer.
Based on case-control data, researchers calculated that women who consumed 1 ounce of alcohol a day, about two drinks, had a 40 percent greater risk of contracting breast cancer than non-drinkers.
Estimates derived from follow-up data showed women who had two drinks daily were 70 percent more likely to get breast cancer than teetotalers.
At lower intakes, researchers found a "weak or modest" link between drinking and breast cancer.
The scientists pointed out that despite their apparent linkage, the health benefits of moderate consumption of alcohol still may outweigh drawbacks in many cases.
A study published this week in the New England Journal of Medicine indicates moderate drinking appears to decrease sharply the risk that women will suffer a heart attack or the most common type of stroke.
Dr. Susan Chu, of the federal Centers for Disease Control in Atlanta, said a control case study she conducted of 3,252 women with breast cancer found no increased risk of such cancer from drinking.
"In my opinion, with existing data, it is far too early to make strong recommendations for most women to stop drinking," she said.