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Evidence Shows That Alcohol Is Likely Cause of Cancer At Multiple Sites, Says Reviewer

Alcohol is one of the most widely consumed psychoactive substances in the world. The US 2014 National Survey on Drug Use and Health found that almost 88% of people over the age of 18 report having consumed alcohol at some point in their life and more than half have drank alcohol in the past month.  Although it offers many social and mood benefits, alcohol consumption is estimated to contribute to a significant proportion of the global economic, social, and health burden.

A recent report by the World Health Organization (WHO) in 2014 attributed 5.9% of all deaths worldwide each year (roughly 3.3 million) to harmful alcohol use.  The WHO report also states that harmful alcohol use has been shown to have a causal relationship with 200 adverse health conditions (e.g. cirrhosis and alcohol dependence) and even influences the clinical outcomes of infectious diseases including tuberculosis and pneumonia.

Cancer and Alcohol

One association that has been less clear however is the relationship between alcohol consumption and cancer.  Decades of research and reporting on the association between the two has often only resulted in equivocal statements that do not fully commit to a conclusion of causality.  Some of this ambiguity is for good reason, and stems from the underlying complexity of these cancers or is attributable to the strength of the evidence (or lack thereof) given the designs and limitations of the   available studies.  Over time though, more evidence has been mounting, particularly from larger observational studies, demonstrating that the ‘link’ between alcohol and some types of cancer may indeed be causal.

Alcohol As Cause

Now, a recent review in the journal Addiction authored by Jennie Connor, from the Department of Preventive and Social Medicine at the University of Otago in New Zealand, takes aim at summarizing the most recent data that support a causal association between alcohol consumption and cancer.  Dr. Connor believes that there is enough evidence to conclusively state that alcohol is a cause of the disease.  Specifically, she reviews the direct evidence that alcohol can cause cancer in seven sites throughout the body in the oropharynx, larynx, oesophagus, liver, colon, rectum and female breast.

Connor’s conclusion is based on comprehensive reviews published over the past decade, some from a number of organizations including the World Cancer Research Fund and American Institute for Cancer Research, the International Agency for Research on Cancer, and the Global Burden of Disease Alcohol Group, that indicate there is a dose-response relationship between alcohol and these cancers.  Evidence appears to be most strong for cancers of the mouth, pharynx, and oesophagus where consumption of at least 50 grams of alcohol per day (equivalent to about 4 beers) was associated with a relative risk of cancer ranging from 4-7 compared to no drinking.  Furthermore, this risk may be reversible for the latter two cancer types, whereby cessation of drinking can attenuate risk over time. Weaker was the support for colorectal, liver and breast cancers, in which relative risk was about 1.5 for similar daily alcohol intake.

Lower Doses

Even light to moderate drinking may put one at risk according to Connor’s review.  She cites newer research by Cao et al. (2015), who used data from two prospective US cohort studies, and found that women who drank just one alcoholic beverage a day were already at a higher risk for breast cancer and that their total risk of cancer was also increased. Similar conclusions are supported by data from the United Kingdom’s Million Women cohort study.  Furthermore, smoking has been shown to compound these risks, particularly for cancers of the mouth, pharynx, larynx and esophagus.

Mechanisms

Besides the the evidence from observational studies, Connor provides a brief discussion of the mechanisms by which alcohol might cause cancer at some sites but not others. One reason could be from DNA damage due to acetaldehyde, a carcinogenic metabolite produced during the metabolism of ethanol. But genetic factors are also thought to play a role as they do in many cancers. Breast tissue seems to be particularly sensitive to alcohol, which may interfere with  estrogen metabolism, and appears to be separate from other cancer-causing pathways. 

Overall the interplay between these mechanisms and factors are complex and not entirely understood, so Connor cautions that the biological mechanisms must be supported by sound, consistent and robust epidemiological research to ultimately provide a strong conclusion. 

Limitations

Much of the skepticism and criticism towards the evidence that alcohol causes cancer, or the levels at which it may do so, is based on the limitations of the studies which have addressed the issue.  Chief among these problems is estimating consumption via self-report.  Consumers commonly underestimate and/or underreport their consumption but this effect varies by sex, socioeconomic status, and country, making it difficult to statistically correct for.  There is also a lack of data regarding the effect that patterns of drinking (binge vs average) have on these associations.  Better attention must be paid, not just to the average amount of alcohol consumed over a given time period, but also to the frequency and ‘other dimensions’ of consumption.  Another problem stems from the underestimation of the cancer effect caused by including former but now non- drinkers in the abstainer reference group.  Lastly, there is the potential for residual confounders to  affect the outcome by cancer-type. 

Despite these criticisms of the research, Connor firmly concludes that ‘there is strong evidence that alcohol causes cancer at seven sites, and probably others’ and that population-wide reduction in alcohol use has the potential to greatly impact the incidence of many of these diseases.  She points out that some public health officials around the world have begun to consider cancer risk in the development of alcohol consumption recommendations.  The UK specifically has initiated a campaign to educate the public on cancer risks associated with alcohol intake. Additionally, she takes aim at the alcohol industry and its promotion of health benefits from drinking, particularly as the current scientific evidence cannot support a safe level of alcohol consumption with respect to cancer risk. 

Reactions To The Review

In an article published in a New Zealand news site, Robert Brewer of the New Zealand Spirits industry voiced some protest, calling the real story “more complicated” and emphasizing that many other factors must be considered.  Dr Samir Zakhari, who works for the Distilled Spirits Council of the United States, also thinks the story is more complex.  In an editorial piece written by Professor Doug Sellman, Dr. Zakhari is quoted as saying that not enough consideration is given to “interactions between lifestyle, sociocultural and genetic issues”.  Zakhari even goes one step farther and takes aim at Connor directly, accusing her of “cherry-picking data”.

However, Professor Sellman, who is director of the National Addiction Centre at the University of Otago thinks that these critiques amount to industry obfuscation.  Sellman emphasizes the enormous burden that alcohol has on society in New Zealand and the fact that 30 per cent of all alcohol-related deaths are due to cancer.  So the battle will continue to play out between the industry and academic research, but it seems clear that the evidence is stacking up in support of a direct link for alcohol causing cancer.

References:

Connor 2016 : https://tinyurl.com/h2ubun2

Cao et al, 2015: https://tinyurl.com/qgrrjuw

https://tinyurl.com/jz68h25

https://tinyurl.com/zjo7b9j   ■

 


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