We’ve mentioned it in passing before, but it’s not exactly common knowledge that alcohol is a known carcinogen—it causes cancer. According to the National Cancer Institute, “The research evidence indicates that the more alcohol a person drinks—particularly the more alcohol a person drinks regularly over time—the higher his or her risk of developing an alcohol-associated cancer.” They continue, “Based on data from 2009, an estimated 3.5 percent of all cancer deaths in the United States (about 19,500 deaths) were alcohol related.”
The U.S. government classifies moderate drinking as 1 drink or less per day for women and 2 drinks or less per day for men. Heavy drinking is 3+ drinks per day or 7+ drinks per week for women and 4+ drinks per day or 14+ drinks per week for men. The National Cancer Institute says, “There is a strong scientific consensus of an association between alcohol drinking and several types of cancer.” You can see them in the highlighted regions on our diagram.
Head and Neck Cancer
One of those families of cancer is often referred to as head and neck cancers: those of the oral cavity (mouth), pharynx (part of the throat), and larynx (the voice box). Over 500,000 new cases of these cancers are diagnosed annually, and many people will die because of the disease. According to the National Institute on Alcohol Abuse and Alcoholism, “Research suggests that just as some genes may protect individuals against alcoholism, genetics also may determine how vulnerable an individual is to alcohol’s carcinogenic effects”. Having said that, studies have found that 3.5+ drinks per day translates to a 2-3 times greater risk of developing these cancers. That risk is even greater for drinkers who also smoke. Approximately 75% of these cancers are believed to be caused by the use of both tobacco and alcohol. Before Huntsman Cancer Institute’s Dr. Mia Hashibe (we’ve written about her work before) was at HCI, she led a study at the International Agency for Research on Cancer on the interactions between using tobacco and alcohol and the risk of developing head and neck cancer.
In studies like this, the general population is anyone who doesn’t use tobacco or alcohol, and those people are considered to have an odds ratio of 1 so the groups can be easily compared. This graph shows that those who used alcohol were 1.06 times more likely than the general population to develop head and neck cancer, those who used tobacco were 2.37 times more likely to develop the cancer, and those who used both tobacco and alcohol were 5.73 times more likely to develop head and neck cancer than those in the general population. So clearly, risk is elevated for those who use alcohol or tobacco and the risk for those who use both is more than additive (5.73 > 1.06 + 2.37). In fact, it’s more than multiplicative (5.73 > 1.06 x 2.37).
The effect is even more severe with laryngeal cancer, one of the three types of head and neck cancer.
If results are broken down by age, you can see the effect is most pronounced in those between the ages of 45 and 60.
Alcohol consumption is also linked to liver cancer—in fact, it’s a primary cause of the disease—breast cancer, and colorectal cancer.
In terms of breast cancer, researchers have seen that women who drink more than 45 grams per day (this is approximately the same as drinking a single shot) had 1.5 times the risk of non-drinkers. Said differently, for every 10 grams ingested per day, researchers saw a 7-12% increase in the risk of developing breast cancer.
When it comes to colorectal cancer, scientists saw that drinking more than 50 grams per day (slightly more than a single shot) translates to a risk of developing the cancer 1.5 times that of non-drinkers. For every 10 grams ingested per day there was a 7% increase in risk.
Even light drinking (0.5-1 drinks per day) is associated with a “mild increase in the incidence of breast cancer in women and colorectal cancer in men”.
How it Happens
The thing that gives alcohol it’s effects is a chemical called ethanol, or ethyl alcohol. When ingested, an enzyme in the body called alcohol dehydrogenase converts ethanol to acetaldehyde. Acetaldehyde is then further converted to acetate by another enzyme called aldehyde dehydrogenase. Acetate isn’t harmful to the body, and is eventually broken down into some of the more common chemicals in the human body: water and carbon dioxide. However, acetaldehyde—the step that comes before acetate—is a known carcinogen.
Exactly how acetaldehyde causes cancer is still up for debate. Some studies suggest it may interfere with the process of copying DNA when cells split—making cells with mutations that could become cancer. Others theorize that it might inhibit DNA repair, a complicated process which generally fixes the mistakes in DNA strands before they can cause problems. Still others suggest acetaldehyde causes literal breaks in both strands of DNA, permanently changing it.
Acetaldehyde is usually converted to acetate rather rapidly, but it still has enough time to do damage. This is especially the case when acetaldehyde builds up as a result of alcohol being consumed at a greater rate than the body can convert the chemical into acetate. It can do significant damage to the liver and does less (but still impactful) damage to the pancreas, brain, and gastrointestinal tract.