In a study of 100,000 women followed for 28 years, those who consumed as few as three glasses of wine per week had a 15 percent increase in breast cancer risk, and this risk increased with higher alcohol consumption (JAMA, November 2, 2011). Two drinks a day increased the risk by 51 percent. Those who drank fewer than three glasses of wine a week had the same breast cancer risk as those who did not drink.
Binge drinking and cumulative alcohol intake throughout adult life also increased risk for breast cancer. A woman can reduce her risk for breast cancer by omitting a glass of wine with dinner, and by avoiding overweight and exercising.
Red wine raised cancer risk as much as a comparable amount of beer. A 5-ounce glass of wine contains the same amount of alcohol as 12 ounces of beer or 2/3rds of a shot glass of alcohol.
Since drinking alcohol has also been associated with reduced heart attack risk, the study suggests that a woman should drink fewer than three glasses of wine per week. High levels of estrogen are linked to breast cancer and alcohol raises blood levels of estrogen.