Researchers followed more than 1.2 million middle-aged women for an average of seven years. The women were participants in the ongoing Million Women Study in the U.K.
Those who drank alcohol consumed on average one drink a day. These women had an increased cancer risk with increasing alcohol intake, especially for cancers of the breast, liver, rectum, mouth, throat, and esophagus.
Based on their findings, the researchers estimated that alcohol could be to blame for 13% of these cancers in women.
The link between alcohol and breast cancer has been extensively researched and reported on, but the study is among the first to link low-to-moderate alcohol consumption to other cancers in women.
"There were no minimum levels of alcohol consumption that could be considered to be without risk," cancer epidemiologist and study researcher Naomi Allen, DPhil, of the University of Oxford, tells WebMD.
Alcohol and Breast Cancer
Most of the excess cases were breast cancers. Allen and colleagues concluded that as many as 11% of breast cancers can be attributed to alcohol consumption.
Last year, about 250,000 women were diagnosed with invasive and non-invasive breast cancers in the U.S., according to the American Cancer Society. The latest research suggests that 27,000 of these cancers were alcohol related.
The study also shows that:
- Women who drank only wine had the same risk for developing cancer as those who drank beer, spirits, or a combination of alcoholic beverages.
- Less than 2% of the women in the study regularly consumed more than three drinks a day, but each additional drink increased risk.
- Women who smoked and drank alcohol had an increased risk of oral, throat, and esophageal cancer that was greater than the risk associated with smoking alone.
Allen says the findings cannot be extrapolated to men, because they were not included in the study. Most of the research on alcohol and cancer in men has been limited to heavy drinkers, but Allen says it is likely that low-to-moderate alcohol consumption increases cancer risk in men as well as women.
'No Safe Level of Alcohol'
In an editorial accompanying the study, cardiologist Michael S. Lauer, MD, and cardiovascular epidemiologist Paul Sorlie, PhD, of the National Heart, Lung and Blood Institute noted that the study's enormous size and strong design will strongly influence the debate about alcohol and health.
"From the standpoint of cancer risk, the message of this report could not be clearer," they wrote. "There is no level of alcohol consumption that can be considered safe."
Numerous studies suggest that moderate alcohol consumption can lower the risk of heart disease, but Lauer tells WebMD that these studies are not conclusive.
"Even if there are modest beneficial cardiovascular effects, we still don't have a clear picture of the overall risks and benefits of low-to-moderate alcohol consumption," he says. And because heart disease kills mostly elderly women, and because more middle-aged women die from cancer, the findings seem to suggest that the risks of drinking outweigh the benefits in this age group, he says.
"It might be reasonable to suspect that many women in the lay public who are asking physicians about any possible safe effects of alcohol are middle-aged: for this large group, the only reasonable recommendation we can make is that there is no clear evidence that alcohol has medical benefits," Lauer and Sorlie wrote.