Most people sipping a beer or drinking a glass of wine right now are probably unaware that the World Health Organization (WHO) International Agency for Research on Cancer (IARC) has classified alcohol as carcinogenic to humans, which is the the most dangerous classification that any substance can receive from the IARC. Apparently alcohol consumption increases the risk of cancer in the head and neck, esophagus, liver, breast, colorectal, skin, prostate, stomach, gallbladder, and pancreas. Unfortunately, alcohol induced cancer killed 621,000 people in 2017 alone according to the Institute of Health Metrics and Evaluation (IMHE). This is equivalent to 1,700 deaths every single day, which is more than 1 death every minute.

Alcohol, which has the scientific name ethanol, is proven to be toxic to cells, with cell cultures exposed to 5-10% alcohol dying within an hour and cell cultures exposed to 30-40% alcohol dying within 15 minutes. When someone consumes an alcoholic beverage ethanol kills cells wherever it touches the body, especially in the oral cavity, pharynx, and esophagus. According to a scientific study, stem cells in the deeper layers of the mucosa become activated and begin dividing in response to cells dying from ethanol. There is always a chance of errors when stem cells divide, which can result in mutations of DNA and chromosomes, and these mutations can possibly cause cancer. This situation is exacerbated by the fact that stem cells are extra sensitive to other carcinogens in the body during cell division.

This is not the only way that alcohol can cause cancer. Alcohol is broken down into acetaldehyde by the liver, i.e. acetaldehyde is the primary metabolite of alcohol, and acetaldehyde is mutagenic and carcinogenic. Acetaldehyde is carcinogenic in several different ways: it can form adducts on DNA much like the carcinogens in cigarettes, it inhibits DNA synthesis, it inhibits DNA repair, it causes point mutations in human lymphocytes, it delays cell cycle progression, and more.

Beyond ethanol and acetaldehyde, there are actually 16 other carcinogens that have previously been found in alcoholic beverages including acrylamide, aflatoxins, arsenic, benzene, cadmium, ethyl carbamate, formaldehyde, furan, glyphosate, lead, 3-MCPD, 4-methylimidazole, N-nitrosodimethylamine, pulegone, ochratoxin A, and safrole. That being said, proper manufacturing processes can eliminate some of these.

Another way that alcohol can cause cancer is by producing reactive oxygen species when it is metabolized by the liver, while simultaneously this metabolism process reduces anti-oxidants. This leaves liver cells susceptible to oxidation, which can cause chemical and cellular changes that can lead to cancer.

It has been shown that the cancer risk from alcohol increases in a dose-dependent fashion, suggesting damage accumulates with each drink. Indeed, a study found that alcohol induced cancer risk is most correlated with lifetime cumulative alcohol consumption. Thus, alcoholics are most at risk of alcohol induced cancer, but light drinking and binge drinking can lead to increased cancer risk as well. One study found that light drinkers, meaning someone that drinks at the most 1 drink per day, are at a higher risk of oral cavity, pharynx, esophagus, and breast cancer. This result is confirmed by another study. Also, periodic binge drinking has been shown to increase the risk of cancer.

Therefore, the trend is clear. No matter what someone’s alcohol consumption patterns are, whether it be 1 drink a day, binge drinking once a week, or outright alcoholism, the risk of cancer is increased due to the toxic effects of alcohol itself and its carcinogenic metabolite acetaldehyde. Indeed, one study concluded that there is no safe threshold for alcohol consumption due to the cancer risk, so not even a drink once in awhile is necessarily ok. This is especially true since alcohol is an addictive drug, and for a large fraction of the population it is hard to just have 1 drink, with a smaller fraction of the population getting hooked on the first drink and going on an alcoholic binge. The same study also concludes that reducing alcohol consumption is an underemphasized cancer prevention strategy.

Another thing to be aware of is that genetics can play a role in cancer risk from alcohol. Alcohol dehydrogenase is the enzyme which breaks down alcohol into acetaldehyde in the liver. Some people have a genetic variation which causes a ‘super active’ form of this enzyme to be released, speeding up the conversion of alcohol into acetaldehyde and increasing the risk of cancer.

There is another enzyme called aldehyde dehydrogenase 2 (ALDH2), which breaks down acetaldehyde into non-toxic compounds. Some people have a gene which causes a defective form of this enzyme to be produced, which results in acetaldehyde building up in the body. This causes unpleasant side effects which may cause people with this gene to not drink at all, but if someone with this gene gets used to the side effects and drinks anyways then they are at a higher risk of getting cancer.

Finally, if someone already has cancer then they really should not drink alcohol. A few studies show that alcohol consumption increases the risk of secondary cancers. Also, if someone is smoking cigarettes, then alcohol consumption is more likely to cause cancer.

Thus, while most drinkers generally think that the biggest risk of alcohol is getting a hangover or blacking out, long term one of the primary risks of alcohol use is cancer, and there is plenty of scientific evidence and statistics to prove this. These studies also show that even light drinking increases cancer risk, and there is no safe amount of alcohol consumption. Therefore, it is best to not drink alcohol at all.