Alcohol as a cause
What is alcohol?
Alcohol is the common term for ethanol or ethyl alcohol, a chemical substance found in beer, wine, and liquor, as well as in some medicines, mouthwashes, household products, and essential oils (scented liquids taken from plants). Alcohol is produced by the fermentation of sugars and starches by yeast.
The main types of alcoholic drinks and their alcohol content are as follows:
- Beers and hard ciders: 3-7 percent alcohol
- Wines, including sake: 9-15 percent alcohol
- Wines fortified with liquors, such as port: 16-20 percent alcohol
- Liquor, or distilled spirits, such as gin, rum, vodka, and whiskey, which are produced by distilling the alcohol from fermented grains, fruits, or vegetables: usually 35-40 percent alcohol (70-80 proof), but can be higher
According to the National Institute on Alcohol Abuse and Alcoholism, a standard alcoholic drink in the United States contains 14.0 grams (0.6 ounces) of pure alcohol. Generally, this amount of pure alcohol is found in:
- 12 ounces of beer
- 8 ounces of malt liquor
- 5 ounces of wine
- 1.5 ounces or a "shot" of 80-proof liquor
The federal government’s Dietary Guidelines for Americans 2010 defines moderate alcohol drinking as up to one drink per day for women and up to two drinks per day for men. Heavy alcohol drinking is defined as having more than three drinks on any day or more than seven drinks per week for women and more than four drinks on any day or more than 14 drinks per week for men.
What is the evidence that alcohol drinking is a cause of cancer?
Based on extensive reviews of research studies, there is a strong scientific consensus of an association between alcohol drinking and several types of cancer. In its Report on Carcinogens, the National Toxicology Program of the US Department of Health and Human Services lists consumption of alcoholic beverages as a known human carcinogen. 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. 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.
Clear patterns have emerged between alcohol consumption and the development of the following types of cancer:
Head and neck cancer: Alcohol consumption is a major risk factor for certain head and neck cancers, particularly cancers of the oral cavity (excluding the lips), pharynx (throat), and larynx (voice box). People who consume 50 or more grams of alcohol per day (approximately 3.5 or more drinks per day) have at least a two to three times greater risk of developing these cancers than nondrinkers. Moreover, the risks of these cancers are substantially higher among persons who consume this amount of alcohol and also use tobacco.
Esophageal cancer: Alcohol consumption is a major risk factor for a particular type of esophageal cancer called esophageal squamous cell carcinoma . In addition, people who inherit a deficiency in an enzyme that metabolizes alcohol have been found to have substantially increased risks of alcohol-related esophageal squamous cell carcinoma.
Liver cancer: Alcohol consumption is an independent risk factor for, and a primary cause of, liver cancer (hepatocellular carcinoma). (Chronic infection with hepatitis B virus and hepatitis C virus are the other major causes of liver cancer.)
Breast cancer: More than 100 epidemiologic studies have looked at the association between alcohol consumption and the risk of breast cancer in women. These studies have consistently found an increased risk of breast cancer associated with increasing alcohol intake. A meta-analysis of 53 of these studies (which included a total of 58,000 women with breast cancer) showed that women who drank more than 45 grams of alcohol per day (approximately three drinks) had 1.5 times the risk of developing breast cancer as nondrinkers (a modestly increased risk) (7). The risk of breast cancer was higher across all levels of alcohol intake: for every 10 grams of alcohol consumed per day (slightly less than one drink), researchers observed a small (7 percent) increase in the risk of breast cancer.
The Million Women Study in the United Kingdom (which included more than 28,000 women with breast cancer) provided a more recent, and slightly higher, estimate of breast cancer risk at low to moderate levels of alcohol consumption: every 10 grams of alcohol consumed per day was associated with a 12 percent increase in the risk of breast cancer.
Colorectal cancer: Alcohol consumption is associated with a modestly increased risk of cancers of the colon and rectum. A meta-analysis of 57 cohort and case-control studies that examined the association between alcohol consumption and colorectal cancer risk showed that people who regularly drank 50 or more grams of alcohol per day (approximately 3.5 drinks) had 1.5 times the risk of developing colorectal cancer as nondrinkers or occasional drinkers (9). For every 10 grams of alcohol consumed per day, there was a small (7 percent) increase in the risk of colorectal cancer.
Research on alcohol consumption and other cancers:
Numerous studies have examined the association between alcohol consumption and the risk of other cancers, including cancers of the pancreas, ovary, prostate, stomach, uterus, and bladder. For these cancers, either no association with alcohol use has been found or the evidence for an association is inconsistent.
However, for two cancers—renal cell (kidney) cancer and non-Hodgkin lymphoma (NHL)—multiple studies have shown that increased alcohol consumption is associated with a decreased risk of cancer (10, 11). A meta-analysis of the NHL studies (which included 18,759 people with NHL) found a 15 percent lower risk of NHL among alcohol drinkers compared with nondrinkers (11). The mechanisms by which alcohol consumption would decrease the risks of either renal cell cancer or NHL are not understood.
How does alcohol increase the risk of cancer?
Researchers have identified multiple ways that alcohol may increase the risk of cancer, including:
- metabolizing (breaking down) ethanol in alcoholic drinks to acetaldehyde, which is a toxic chemical and a probable human carcinogen; acetaldehyde can damage both DNA (the genetic material that makes up genes) and proteins
- generating reactive oxygen species (chemically reactive molecules that contain oxygen), which can damage DNA, proteins, and lipids (fats) through a process called oxidation
- impairing the body’s ability to break down and absorb a variety of nutrients that may be associated with cancer risk, including vitamin A; nutrients in the vitamin B complex, such as folate; vitamin C; vitamin D; vitamin E; and carotenoids
- increasing blood levels of estrogen, a sex hormone linked to the risk of breast cancer
Alcoholic beverages may also contain a variety of carcinogenic contaminants that are introduced during fermentation and production, such as nitrosamines, asbestos fibers, phenols, and hydrocarbons.
How does the combination of alcohol and tobacco affect cancer risk?
Epidemiologic research shows that people who use both alcohol and tobacco have much greater risks of developing cancers of the oral cavity, pharynx (throat), larynx, and esophagus than people who use either alcohol or tobacco alone. In fact, for oral and pharyngeal cancers, the risks associated with using both alcohol and tobacco are multiplicative; that is, they are greater than would be expected from adding the individual risks associated with alcohol and tobacco together.
Can a person’s genes affect their risk of alcohol-related cancers?
A person’s risk of alcohol-related cancers is influenced by their genes, specifically the genes that encode enzymes involved in metabolizing (breaking down) alcohol.
For example, one way the body metabolizes alcohol is through the activity of an enzyme called alcohol dehydrogenase, or ADH. Many individuals of Chinese, Korean, and especially Japanese descent carry a version of the gene for ADH that codes for a "superactive" form of the enzyme. This superactive ADH enzyme speeds the conversion of alcohol (ethanol) to toxic acetaldehyde. As a result, when people who have the superactive enzyme drink alcohol, acetaldehyde builds up. Among people of Japanese descent, those who have this superactive ADH have a higher risk of pancreatic cancer than those with the more common form of ADH.
Another enzyme, called aldehyde dehydrogenase 2 (ALDH2), metabolizes toxic acetaldehyde to non-toxic substances. Some people, particularly those of East Asian descent, carry a variant of the gene for ALDH2 that codes for a defective form of the enzyme. In people who have the defective enzyme, acetaldehyde builds up when they drink alcohol. The accumulation of acetaldehyde has such unpleasant effects (including facial flushing and heart palpitations) that most people who have inherited the ALDH2 variant are unable to consume large amounts of alcohol. Therefore, most people with the defective form of ALDH2 have a low risk of developing alcohol-related cancers.
However, some individuals with the defective form of ALDH2 can become tolerant to the unpleasant effects of acetaldehyde and consume large amounts of alcohol. Epidemiologic studies have shown that such individuals have a higher risk of alcohol-related esophageal cancer, as well as of head and neck cancers, than individuals with the fully active enzyme who drink comparable amounts of alcohol . These increased risks are seen only among people who carry the ALDH2 variant and drink alcohol—they are not observed in people who carry the variant but do not drink alcohol.
Can drinking red wine help prevent cancer?
Researchers conducting studies using purified proteins, human cells, and laboratory animals have found that certain substances in red wine, such as resveratrol, have anticancer properties. Grapes, raspberries, peanuts, and some other plants also contain resveratrol. However, clinical trials in humans have not provided evidence that resveratrol is effective in preventing or treating cancer. Few epidemiologic studies have looked specifically at the association between red wine consumption and cancer risk in humans.
What happens to cancer risk after a person stops drinking alcohol?
Most of the studies that have examined whether cancer risk declines after a person stops drinking alcohol have focused on head and neck cancers and on esophageal cancer. In general, these studies have found that stopping alcohol consumption is not associated with immediate reductions in cancer risk; instead, it may take years for the risks of cancer to return to those of never drinkers.
For example, a pooled analysis of 13 case-control studies of cancer of the oral cavity and pharynx combined found that alcohol-associated cancer risk did not begin to decrease until at least 10 years after stopping alcohol drinking. Even 16 years after they stopped drinking alcohol, the risk of cancer was still higher for ex-drinkers than for never drinkers.
In several studies, the risk of esophageal cancer was also found to decrease slowly with increasing time since stopping alcohol drinking. A pooled analysis of five case–control studies found that the risk of esophageal cancer did not approach that of never drinkers for at least 15 years after stopping alcohol drinking.
Is it safe for someone to drink alcohol while undergoing cancer chemotherapy?
As with most questions related to a specific individual’s cancer treatment, it is best for a patient to check with their health care team about whether or not it is safe to drink alcohol during or immediately following chemotherapy treatment. The doctors and nurses administering the treatment will be able to give specific advice about whether drinking alcohol is safe with particular chemotherapy drugs and/or other medications prescribed along with chemotherapy.
The content of this page was heavily sourced from the National Cancer Institue 2014.