December 14, 2017 | by City of Hope
A New Zealand study has found “strong evidence” that alcohol causes seven types of cancer — oropharynx, larynx, esophagus, liver, colon, rectum and breast cancer — and “probably others” such as pancreas, prostate and skin cancer.
While men who drink more than four alcoholic beverages a day and women who drink more than three are in the greatest danger, the assessment, published in Addiction Journal, claims that even moderate alcohol consumption puts people at risk.
"The highest risks are associated with the heaviest drinking but a considerable burden is experienced by drinkers with low to moderate consumption," said study author Jennie Connor, professor of epidemiology in the Department of Preventive and Social Medicine at the University of Otago, New Zealand. “There is no argument, on current evidence, for a safe level of drinking with respect to cancer.”
Leslie Bernstein, Ph.D., a professor in the Department of Population Sciences, qualified the study’s findings by suggesting that there is more nuance to the relationship.
I am always reluctant to state that some factor causes cancer, except with regard to cigarette smoking causing lung cancer,” Bernstein said. “When we say ‘alcohol causes seven cancers,’ we neglect the fact that many factors may cause these cancers and only a few people who drink alcohol will develop one of these cancers due to their drinking alcohol and not due to other things, or a combination of other things with alcohol.”
For the study, Connor looked at 10 years' worth of data from numerous agencies, including the World Cancer Research Fund. She found that drinking 50 grams of alcohol per day — about 2.6 beers, or three six-ounce glasses of wine — resulted in a four to seven times greater risk of cancer in the oropharynx, larynx and esophagus, and a 1.5 times greater risk of the other types, compared to consuming no alcohol.
According to her findings, alcohol directly caused approximately 5.8 percent of cancer deaths worldwide in 2012.
Alcohol consumption is one of the most important known risk factors for human cancer and potentially one of the most avoidable factors, but it is increasing worldwide,” Connor wrote. She also noted that the risks, particularly for cancers of the mouth and throat, increase even more for people who also smoke.
Scientists aren't sure how alcohol causes cancer, but acetaldehyde, a compound that is formed when alcohol breaks down in the body, has been found to damage the DNA of cells in the mouth, throat, esophagus and liver. Stopping alcohol consumption, however, seems to lower one’s risk of cancer of the larynx, throat and liver, with the risk continuing to drop the longer one abstains, according to Connor’s analysis.
This finding contradicts previous studies showing that alcohol consumption, such as drinking red wine daily, could offer protection against cancer. In fact, Connor’s study stated, “Promotion of health benefits from drinking at moderate levels is seen increasingly as disingenuous or irrelevant in comparison to the increase in risk of a range of cancers.”
Bernstein remained skeptical of some of the study’s conclusions and noted in particular “the difficulty in separating out the effects of cigarette smoking, which are so often a more potent driver of cancer risk (at least for oral cancers and the one subtype of esophageal cancer that is impacted by alcohol — squamous cell esophageal cancer). For the oral cancers, it is difficult to determine whether alcohol has an independent effect.”
I think the author did not say enough about the combination of other risk factors for each of the seven cancers,” Bernstein said. While she allowed that “there is substantial evidence that alcohol intake is associated with risk of the seven cancers, epidemiological studies are not able to provide sufficient evidence of causation.”
For example, Bernstein noted, “alcohol is not the major determinant of oral cancers or squamous cell cancer of the esophagus. Most important for those cancers is not to smoke. For liver cancer, hepatitis is a major risk factor. Many factors contribute to breast cancer and colorectal cancer. Alcohol is not a major risk factor for these cancers — there are so many other factors that are important determinants of risk.”
To put all this in perspective, she concluded, “If a person were to drink only one to two drinks a week, their potential for developing one of these cancers would remain quite low — and at these levels we cannot be certain that there is any direct causation.”
So, perhaps no one need give up that Saturday night gin and tonic just yet. But stopping at one may make a real difference.