Web MD -- Some studies have linked drinking alcohol to an increased risk for breast cancer, and now new research suggests that even moderate to light alcohol intake may raise a woman's risk.
Consistently drinking as little as three alcoholic beverages a week was associated with a small -- 15% -- increase in breast cancer risk in the study.
Drinking at least two glasses of wine or beer a day or two cocktails a day -- was associated with about a 50% increase in risk.
The study, which appears in the Nov. 3 issue of The Journal of the American Medical Association, ultimately found cumulative lifetime alcohol exposure to be an important predictor of breast cancer risk.
The study included nearly 106,000 nurses enrolled in one of the largest, longest, and most comprehensive women's health studies ever conducted in the U.S.
Between 1980 and 2008, the women were surveyed about their drinking habits eight separate times, allowing the researchers to evaluate the role of drinking patterns on breast cancer risk.
The women were between the ages of 34 and 59 when first asked about their alcohol intake in 1980. The women were asked about alcohol intake during early adulthood -- ages 18 to 22, 25 to 30, and 35 to 40.
Binge drinking was associated with an increase in breast cancer risk, as was cumulative alcohol intake over time.
But frequency of drinking -- how often women drank during the week and when -- did not appear to influence risk. The key component was how much you consistently drank over time.
"There is both good and bad news for women in our findings," researcher Wendy Y. Chen, MD, MPH, of Brigham and Women's Hospital and Harvard Medical School, tells WebMD.
"It appears that by changing their drinking behavior, women can impact their risk for breast cancer, no matter when in life they do this. That is the good news. The bad news is you can't really change what you did in the past."
The American Cancer Society (ACS) recommends that women who choose to drink alcohol limit their intake to no more than one drink per day.
The latest findings from the study do not change this recommendation, ACS vice president of epidemiology Susan Gapstur, PhD, tells WebMD.
"This study and others found that heavy drinking was associated with the biggest risk, so the message to avoid heavy drinking is clear," Gapstur says, adding that the message about light to moderate drinking is more nuanced.
That is because moderate alcohol intake may protect the heart and lower a woman's risk for heart attack and stroke.
She recommends that women talk to their doctors and consider their individual risk for breast cancer, heart disease, and stroke.
Chen and colleagues agree, concluding that the risks and benefits of light to moderate alcohol consumption have to be considered on an individual basis.
Breast cancer researcher Steven A. Narod, MD, PhD, says the surprising finding from the study is that the effect of alcohol consumption on breast cancer risk appears to be cumulative.
Narod is chairman of breast cancer research at the Women's College Research Institute in Toronto.
"If alcohol increases risk, it does not come down to how much a woman drank over the last year but how much she drank over the last 20 years," he tells WebMD.
Because most of the breast cancers in the study population occurred in postmenopausal women, Narod says the findings do not really address the role of alcohol use on breast cancers in younger women.
"We know precious little about the role of lifestyle, if any, on the development of breast cancers in premenopausal women," he says.
Avoiding alcohol, maintaining a healthy weight, and exercising have all been linked to a reduction in breast cancer risk in older women.
But Narod believes the importance of these lifestyle factors on breast cancer has been overstated.
"If every woman stopped drinking and every woman who was overweight lost weight, the risk of postmenopausal breast cancer might be reduced by 10%, but that isn't going to happen," he says.
Chen concedes that the impact of lifestyle on breast cancers at the population level may be modest, but she says the impact for an individual woman may be huge.
"It is true that we won't prevent all breast cancers by changing lifestyle, but we will prevent some," she says