The Surgeon General's Report Does Not Show Alcohol Causes Cancer

Alcoholic drinks are the focus of a medical debate. For decades, medical research suggested that red wine had health benefits. Now, the U.S. Surgeon General has warned us that even moderate alcohol consumption causes several cancers.

Alcohol can be dangerously addictive. Why do so many people continue to consume alcohol if it may be so damaging? And how do we establish a causal link of this sort—alcohol causing cancer—when there are so many psychological factors intervening? The Surgeon General's report makes a surprisingly weak case for the causal conclusion. It ignores the findings of animal experiments, fails to consider stress as a third variable, and downplays contrary evidence. The causal conclusion is based on statistical associations from epidemiological studies (i. e., correlations) that cannot establish causation. Only experiments can do that.

Animal Experiments

A properly controlled experiment is the only evidence that truly establishes causation. Since we cannot conduct ethical experiments on humans, animal experiments provide the best available evidence for causation.

The animal evidence is surprisingly weak. In an earlier scientific review of this evidence, 11 relevant experiments were assessed. Two found that alcohol in the drinking water increased the number of tumors in rodents, while nine found that alcohol did not increase cancers (1). While the positive findings deserve to be taken seriously, the preponderance of the research finds that alcohol does not cause cancer. This is striking given the publication bias that generally favors positive findings. The Surgeon General emphasizes research on cellular mechanisms linking alcohol and cancers. Although many different mechanisms were tested, there is no scientific consensus on how exactly alcohol might increase the growth of tumors. So, what is presented as strong causal evidence is actually a real scientific weakness.

The Third Variable Problem

The Surgeon General claimed that alcohol is the third-leading cause of cancer, after obesity and stress. Stress stands out as a potential third variable in respect to alcohol and cancer.

Ask yourself why people drink alcohol. Alcohol is an anti-anxiety drug. People drink to cope with stress in their lives. So how can we separate the effect of alcohol on cancer from the effect of stress? We cannot.

Contradictory Evidence

While the Surgeon General concedes that moderate alcohol consumption may offer health benefits in relation to cardiovascular disease, this evidence is not reviewed and other potential benefits of alcohol are ignored.

One of the fascinating findings from the cardiovascular research is that there is a U-shaped relationship between alcohol consumption and heart disease (1). Moderate drinkers have better cardiovascular health than teetotalers. This result suggests that moderate alcohol consumption can improve immune function. If so, it might also reduce the risk of cancer.

It is hard to disentangle alcohol consumption and stress. Yet, there is one group of people who have low stress but drink more than average. This group is the elite. Wealthy people can be found at fashionable events where alcohol flows freely. They maintain well-stocked drinks cabinets and wine cellars.

The Wealth Paradox

How does one square the fact that wealthy people drink more alcohol and yet have better health, and lead longer lives, than others? One explanation is that money brings improved access to healthcare, better life-extending treatments, and a generally healthier lifestyle. Perhaps the assumed adverse consequences of alcohol consumption are more than offset by the benefits of better healthcare and lifestyle in other respects. As it is, the alcohol-swilling elite live for a decade longer than the less privileged.

Is it possible that their consumption of alcohol produces positive health effects overall? This possibility is rarely addressed by researchers possibly because many are motivated to prevent the ravages of problem drinking.

Perhaps the impact of alcohol on health is mediated by the context. The affluent often drink in positive social settings. They are in the company of members of a large and cohesive social network that helps them to cope with stress.

These contexts can build social support, reduce stress, and improve health. Alcohol may thus facilitate the breaking down of barriers and the formation of friendships.

However one accounts for it, the fact that affluent people are demonstrably healthier despite consuming more alcohol than the rest of the population is embarrassing to the Surgeon General's thesis.

Of course, it is theoretically possible that they would live much longer and still be at greater risk of getting cancer. Consistent with this idea, high-income people are more likely to be diagnosed with cancer. However, this appears to be because they visit doctors more. Despite more cancer diagnoses, their cancer mortality is no different from that of the general population.

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Conclusion

In conclusion, the case that moderate alcohol consumption causes cancer is astonishingly weak. Perhaps it does. Yet the Surgeon General's report lacks scientific rigor.