British researchers surveyed middle-aged women at breast cancer screening clinics about their drinking habits, and tracked their health for seven years.
A quarter of the women reported no alcohol use. Nearly all the rest reported fewer than three drinks a day; the average was one drink a day. Researchers compared the lightest drinkers - two or fewer drinks a week - with people who drank more.
Each extra drink per day increased the risk of breast, rectal and liver cancer, University of Oxford researchers reported Tuesday in the Journal of the National Cancer Institute. The type of alcohol - wine, beer or liquor - didn't matter.
That supports earlier research, but the new wrinkle: Alcohol consumption was linked to esophageal and oral cancers only when smokers drank.
Also, moderate drinkers actually had a lower risk of thyroid cancer, non-Hodgkin's lymphoma and renal cell cancer.
For an individual woman, the overall alcohol risk is small. In developed countries, about 118 of every 1,000 women develop any of these cancers, and each extra daily drink added 11 breast cancers and four of the other types to that rate, the study found.
But population-wide, 13 percent of those cancers in Britain may be attributable to alcohol, the researchers concluded.
Moderate alcohol use has long been thought to be heart-healthy, something the new research doesn't address but that prompts repeated debate about safe levels. U.S. health guidelines already recommend that women consume no more than one drink a day; two a day for men, who metabolize alcohol differently.
"You have to balance all those things out," said Dr. Philip J. Brooks, who researches alcohol and cancer at the National Institutes of Health. "This kind of information is important for people to know and to consult with their physician about the various risk factors they have."