Alcohol is categorized as a class 1 cancer-causing substance. Although the IARC classification doesn’t imply that alcohol is as dangerous as other proven human carcinogens such as benzene and heavy cigarette smoking, the findings should not be overlooked. This is especially true with regard to certain types of cancers and considering that: (1) drinking alcohol is even riskier for women and (2) social attitudes regarding alcohol continue to be extremely permissive, and no cancer warnings exist on any product labels. As is the case with all carcinogens, the risk tends to increase with the overall amount of ethanol consumed. But the danger-threshold has recently become much lower based on current research.
When I first looked into the alcohol-cancer connection, 11 years ago, Dr. Rachel Thompson, Science Programme Manager at the WCRF (World Cancer Research Fund) had said , “If you are drinking a pint of lager or a large glass of wine everyday, then this might not seem like a lot.” She further added, “But the science shows you are increasing your risk of bowel cancer by 18 percent and your risk of liver cancer by 20 percent.”
One serving (12 fluid oz of beer or 5 fluid oz of wine, or 1.5 fluid oz of 80-proof distilled spirits) contains 14 grams of pure ethanol, the type of alcohol in drinks. The data of the 2012 meta study, which Rachel Thompson referred to, was only available for an average consumption of 25, 50 and 100 g/day, which amounted to approximately 1.5, 3 and 6 drinks a day, respectively.
According to the latest data available in 2023 which has caused recommended guidelines to become more strict, one drink per day for a woman increases the risk of liver cancer by 6.1% but that of cirrhosis by 255%; esophageal cancer by 21.9%; of cancer of the oral cavity and pharynx by 61.4%; breast cancer 14.7%. Even at only 5 grams per day, equivalent to only 2.5 drinks per week, the elevated risks are still not negligible:
One drink per day for a male increases the risk of colorectal cancer by 10.7%; esophageal cancer by 21.9%; cancer of the larynx by 24%. Those numbers spike significantly when the dose doubles. At 2.5 drinks per week for males, the increased risk dips below 10% for those cancers, except for oral and pharynx cancers, which get elevated by 13.1%, just as they do for women.
Statistics aside, how does ethanol induce cancers? No clear mechanism has been elucidated but there are many plausible scenarios, according to a 2006 review paper in the Lancet. Acetaldehyde (pictured on the right), which is alcohol’s main metabolite, is genotoxic, especially in genetically susceptible individuals where the acetaldehyde is not as quickly oxidized to the innocuous acetate. There is at least in vitro evidence that acetaldehyde and not alcohol itself does genetic damage in the liver, head, neck and breast. Ethanol also increases estrogen concentration, and it acts as a solvent for tobacco’s carcinogens.
In general why are women even more sensitive to alcohol than men? It is due a number of factors: smaller body size increases the concentration. A higher body fat/water ratio retains more alcohol due to alcohol’s high solubility in fat. Hormonal effects are important too. Finally, women produce smaller quantities of the enzyme alcohol dehydrogenase (ADH), which is released in the liver and breaks down alcohol in the body.
Review Paper of Possible Mechanisms