There is "strong evidence" that alcohol causes seven cancers, and other evidence indicates that it "probably" causes more, according to a new literature review published online July 21 in Addiction.
Epidemiologic evidence supports a causal association of alcohol consumption and cancers of the oropharynx, larynx, esophagus, liver, colon, rectum, and female breast, says Jennie Connor, MB, ChB, MPH, from the Department of Preventive and Social Medicine, University of Otago, in Dunegin, New Zealand.
In short, alcohol causes cancer.
This is not news, says Dr. Connor. The International Agency for Research on Cancer (IARC) and other agencies have long identified alcohol consumption as being causally associated with these seven cancers.
So why did Dr. Connor, who is an epidemiologist and physician, write a new review? Because she wants to "clarify the strength of the evidence" in an "accessible way."
There is "confusion" about the statement, "Alcohol causes cancer," explains Dr. Connor.
Public and scientific discussion about alcohol and cancer has muted the truth about causality, she suggests.
"In the public and the media, statements made by the world's experts are often given the same weight as messages from alcohol companies and their scientists. Overall messages become unclear. For these reasons, the journal [Addiction] has tagged this piece [her review] as 'For Debate,' " she told Medscape Medical News.
The use of causal language in scientific and public discussions is "patchy," she writes.
For example, articles and newspaper stories often use expressions such as "alcohol-related cancer" and "alcohol-attributable cancer"; they refer to a "link" between alcohol and cancer and to the effect of alcohol on "the risk of cancer."
These wordings "incorporate an implicit causal association, but are easily interpreted as something less than cancer being caused by drinking," observes Dr. Connor.
"Stop drinking alcohol" is a catch phrase that could be ― but is not ― akin to "stop smoking," she also suggests.
"Currently, alcohol's causal role is perceived to be more complex than tobacco's, and the solution suggested by the smoking analogy — that we should all reduce and eventually give up drinking alcohol — is widely unacceptable," writes Dr. Connor.
The newly published review "reinforces the need for the public to be made aware of the causal link between alcohol and cancer," said Colin Shevills, from the Alcohol Health Alliance UK, in a press statement.
"Research shows that only around 1 in 10 people [in the UK] are currently aware of the alcohol-cancer link," he said.
"People have the right to know about the impact of alcohol on their health, including its link with cancer, so that they can make informed choices about how much they drink," added Shevills.
The lack of clarity about alcohol causing cancer, Dr. Connor believes, is related to alcohol industry propaganda as well as the fact that the "epidemiological basis for causal inference is an iterative process that is never completed fully."
What the Epidemiology Says
Dr. Connor writes that the strength of the association of alcohol as a cause of cancer varies by bodily site. The evidence is "particularly strong" for cancer of the mouth, pharynx, and esophagus (relative risk, ~4-7 for ≥50 g/day of alcohol compared with no drinking) but is less so for colorectal cancer and liver and breast cancer (relative risk, ~1.5 for ≥50 g/day).
"For cancers of the mouth, pharynx, larynx and oesophagus there is a well-recognized interaction of alcohol with smoking, resulting a multiplicative effect on risk," adds Dr. Connor.
Other cancers are also likely caused by alcohol. Dr. Connor writes that there is "accumulating research" supporting a causal contribution of alcohol to cancer of the pancreas, prostate, and skin (melanoma).
The exact mechanisms as to how alcohol, either alone or in combination with smoking, cause cancer "are not fully understood," although there is some supporting "biological evidence," she says.
One British expert had an opinion about alcohol's carcinogenicity.
In a statement about the new review, Prof Dorothy Bennett, director of the Molecular and Clinical Sciences Research Institute at St. George's, University of London, said: "Alcohol enters cells very easily, and is then converted into acetaldehyde, which can damage DNA and is a known carcinogen."
In the new review, Dr. Connor describes various hallmarks of causality that have been found in epidemiologic studies of alcohol and these seven cancers, such as a dose-response relationship and the fact that the risk for some of these cancers (esophageal, head and neck, and liver) attenuates when drinking ceases.
Current estimates suggest that alcohol-attributable cancers at the seven cancer sites make up 5.8% of all cancer deaths worldwide, she states.
The alcohol industry has a lot at stake, she says, which in turn leads to "misinformation" that "undermines research findings and contradicts evidence-based public health messages."
A recent example comes from New Zealand, where a symposium on alcohol and cancer was covered by national media. An opinion piece by an industry-funded scientist in the capital's daily newspaper disputed the evidence reported from the conference. That essay was entitled: "To Say Moderate Alcohol Use Causes Cancer Is Wrong."
The essay included the statement: "While chronic abusive alcohol consumption is associated with a plethora of health problems including cancer, attributing cancer to social moderate drinking is simply incorrect and is not supported by the body of scientific literature."
But there is no safe level of drinking with respect to cancer, says Dr. Connor, citing research about low to moderate levels of alcohol, which has been covered by Medscape Medical News.
This was also the conclusion of the 2014 World Cancer Report, issued by the World Health Organization's IARC.
The promotion of health benefits from drinking at moderate levels is "seen increasingly as disingenuous or irrelevant in comparison to the increase in risk of a range of cancers," writes Dr. Connor.
Public health campaigns "with clear messages" are needed to spread the word about alcohol's carcinogenicity, she told Medscape Medical News.
"I think that the UK is leading the way. Alcohol consumption as a public health issue has had high exposure in the UK over quite a number of years," said Dr. Connor, who provided links to two awareness campaigns, the Balance campaign, and the Balance Northeast campaign.
Earlier this year, the United Kingdom issued new guidelines on alcohol drinking, recommending that men drink no more than women and warning that any amount of alcohol increases the risk of developing a range of cancers.
Organizations in New Zealand are also taking action. The New Zealand Medical Association, the Cancer Society of New Zealand, and the National Heart Foundation have all adopted evidence-based position statements that "debunk" cardiovascular benefits as a motivation to drink and that highlight cancer risks, Dr. Connor said.