Accumulating evidence suggests that any level of alcohol consumption comes with risks to health. A prime example of this is research on the relationship between alcohol and cancer. Studies suggest that even light to moderate amounts of alcohol may increase risk of certain types of cancers.

 

Alcohol is a carcinogen, or a substance that causes cancer

This may sound like a sensational claim, but alcohol is technically classified as a carcinogen per a report from the National Toxicology Program of the U.S. Department of Health and Human Services. It is also labeled as a group 1 carcinogen by the International Agency for Research on Cancer, along with tobacco, asbestos, benzenes, and other compounds. If this comes as a surprise to you, you aren’t alone. According to a 2019 survey conducted by the American Institute for Cancer Research (AICR), less than half of Americans are aware that alcohol is linked to cancer.

There are many potential mechanisms by which alcoholic beverages may cause cancer:

• The primary metabolic pathway by which ethanol (or alcohol) is broken down produces a toxic, short-lived by-product called acetaldehyde. Acetaldehyde can damage DNA and proteins in cells.
• Furthermore, alcohol increases the production of reactive oxygen species (these are the compounds that antioxidants “quench” or neutralize). These compounds similarly damage components of cells.
• Alcohol impacts our ability to digest, absorb, and metabolize nutrients, and inadequate intake of nutrients, such as folate, is associated with an increased risk of cancer. 
• Because the liver prioritizes alcohol metabolism over other processes, this opens the door for other chemicals, such as tobacco, to exert negative effects on the body.
• The process of making alcoholic beverages may produce or introduce other compounds that increase risk of cancer, such as phenols, nitrosamines, and hydrocarbons [1].

These are just a few examples of potential mechanisms by which alcohol exposure could lead to cancer development. Of course, genetics and other lifestyle factors also likely influence the relationship between alcohol consumption and cancer risk [2].

 

Alcohol and cancer risk: what’s the buzz?

The World Cancer Research Fund (WCRF) Continuous Update Project (CUP) recently updated and re-evaluated the research on how lifestyle factors, such as diet and physical activity, affect cancer risk, publishing their third expert report in 2018 [3]. The findings of this report suggests that alcohol consumption increases the risk of at least six different types of cancer: breast (both pre- and post-menopausal), colorectal, esophageal, liver, stomach, and oral, pharyngeal and laryngeal cancers. 

The expert panel graded the evidence supporting the claim that alcoholic beverages increase risk of these cancers listed above as “strong,” meaning it suggests a “probable” or “convincing” relationship. The findings of the report also suggest that alcohol intake may increase the risk of lung, pancreatic, and skin cancers, though the evidence is "limited." As an exception, risk of kidney cancer was actually decreased with consumption of up to two standard drinks per day, but the relationship was “unclear” at higher levels of alcohol consumption. 

Of note, the expert panel found that consuming two standard drinks per day (30 grams ethanol) or more was associated with increased risk of colorectal cancer. Three or more standard drinks per day may increase the risk of stomach and liver cancers. For the other types of cancer, no threshold of alcohol consumption was identified; in other words, any amount of alcohol may increase risk of developing these cancers.

 

Recent research

A study published earlier this month in The Lancet Oncology generated a lot of buzz in the media and the sober community. The purpose of this study was to update the estimated global burden of cancer cases that are attributable to, or caused by, alcohol consumption. The authors compared levels of alcohol consumption in 2010 (to account for the fact that cancer does not develop overnight) to the expected number of new cancer cases for 2020, and used relative risks for exposure to alcohol from the WCRF-CUP to estimate how many of these new cases were likely caused by alcohol consumption. 

The findings of this study suggest that nearly 740,000 cancer cases globally are attributable to alcohol. Unsurprisingly, the greatest "burden" of these cases was associated with “heavy” or “risky” drinking behaviors (defined as more than 60 grams of ethanol per day and 20 to 60 grams of ethanol per day, respectively). However, a significant portion of cancer cases were linked with what is viewed as a “safe” level of alcohol intake. Moderate drinking (20 grams) contributed to an estimated 14% of cases. Between 35,400 and 145,800 cancer cases were attributable to consumption of fewer than 10 grams of ethanol, or less than a 4-5 ounce portion of red wine. 

The authors of this study believe that these estimates are likely conservative (i.e. an underestimate) for a number of reasons. For example, this study only examined certain cancers where there is a known association with alcohol consumption. When former drinking (lifetime use but not within the last 12 months) was taken into account in a sensitivity analysis, 135,000 additional cases attributable to alcohol were identified. 

While this study provides estimates for the number of cancer cases that might be caused by alcohol use, it does not shed light on mortality rates. A 2013 study published in the American Journal of Public Health estimated cancer deaths attributable to alcohol in the U.S., estimating that alcohol contributes to 3.2 to 3.7% of cancer deaths, or about 19,500 deaths in the year 2009. What is most alarming is that consuming up to 20 grams of alcohol per day (less than two standard drinks) accounted for up to one-third of alcohol-attributable cancer deaths in the U.S. for that year. 

 

Recommendations for alcohol intake and cancer prevention

Based on the available evidence, any amount of alcohol may come with some degree of risk when it comes to cancer. Thus, many respected cancer organizations, including the American Cancer Society, WCRF, and AICR, recommend that, "for cancer prevention, it is best to not drink alcohol." The U.S. Dietary Guidelines for Americans 2020-2025 recommends that those who choose to drink should limit themselves to 2 standard drinks per day for men and one standard drink per day for women (i.e. moderate alcohol consumption). 

Because it is the ethanol and its metabolic by-products that mediate the carcinogenic properties of alcohol, there is no type of alcohol that is better than others in the context of cancer prevention [3]. In other words, red wine is not considered a healthier alternative when it comes to cancer prevention. No matter how “clean,” “non-toxic,” or polyphenol-rich an alcoholic beverage claims to be, it still contains a known carcinogen: ethanol.

Interestingly, a recent observational study in London found that individuals who took a month-long break from alcohol experienced decreases in cancer-related growth factors. While it is not clear whether or how this translates to risk of developing cancer, these results are nevertheless compelling.

 

Trying to cut back on alcohol? Check out this blog post for our top tips on going alcohol-free!

 

References

[1] https://www.cancer.org/cancer/cancer-causes/general-info/known-and-probable-human-carcinogens.html

[2] https://www.cancer.gov/about-cancer/causes-prevention/risk/alcohol/alcohol-fact-sheet#r8 

[3] World Cancer Research Fund/ American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Cancer: A Global Perspective. Continuous Update Project Expert Report 2018. Available at dietandcancerreport.org

[4] https://www.cancer.org/cancer/cancer-causes/diet-physical-activity/alcohol-use-and-cancer.html