Drinking alcohol may cause seven different types of cancer, a new meta-analysis finds.
Previous studies have found an association between drinking alcohol and a higher risk of developing certain cancers, according to the study. However, it was not clear from the studies if drinking alcohol directly caused cancer.
In the new meta-analysis, published on July 21 in the journal Addiction, researchers looked at the major review studies done over the last decade on alcohol and cancer, including reviews from the American Institute for Cancer Research and the International Agency for Research on Cancer.
“There is strong evidence that alcohol causes cancer at seven sites [in the body], and probably others,” Dr. Jennie Connor, a preventive-medicine doctor at the University of Otago in New Zealand and the author of the study, wrote.
The evidence supports “a causal association of alcohol consumption” with cancer in the oropharynx (a part of the throat), the larynx, the esophagus, the liver, the colon, the rectum and the female breast, Connor wrote.
There is also growing evidence suggesting a strong link between alcohol and other cancers, such as prostate, pancreatic and melanoma. However, that evidence is not enough at this point to allow researchers to conclude that there is cause-and-effect relationship for these cancers, according to the study.
Moreover, for each of the seven cancers that are directly linked, previous studies have found that there is a “dose-response relationship,” meaning that the more alcohol a person drinks, the more likely the person is to develop those cancers.
In addition, previous studies have also found that for some cancers, a person’s risk of developing cancer goes down when a person stops drinking, according to the study.
The link between alcohol and cancers of the mouth and throat were stronger than the link between alcohol and other cancers, Connor wrote. For example, drinking more than 50 grams of alcohol a day is was associated with a four to seven times greater risk of developing mouth, throat or esophagus cancer compared with not drinking at all.(The number of grams of alcohol in 1 ounce of a drink can vary. For example, there are 2.4 to 2.8 grams of alcohol in an ounce of wine, but there are 1 to 1.2 grams of alcohol per ounce of beer.)
But drinking that same amount was associated with an approximately 1.5 times greater risk of colorectal, liver or breast cancer, compared with not drinking, according to the study.
Connor noted that the exact mechanism for how alcohol causes cancer is not well-understood, and indeed, it may be different depending on where in the body the cancer occurs.
For example, scientists believe that a compound that forms when alcohol breaks down is responsible for the development of cancers of the mouth, throat, esophagus and liver. The compound, acetaldehyde, is formed when alcohol is digested by saliva or by molecules in the liver. Acetaldehyde comes in direct contact with the tissues of the mouth, throat, esophagus and liver, and can damage the DNA in the cells of these tissues, which can lead to cancer.
But for breast cancer, alcohol may cause cancer by increasing levels of estrogen in the body; the hormone has been linked to the disease, according to the study.
Connor noted that there are limitations to the meta-analysis. In particular, many of the studies included in the analysis relied on people self-reporting how much alcohol they had drank. It is not uncommon for people to say they drank less alcohol than they actually drank, Connor wrote.