Drinking alcohol, even in moderation, raises the risk of cancer, a study has found using an innovative method to test this old question. The extent of the extra risk depends on genetics, and possibly other factors, but it looks like old excuses about how “a little is good for you” probably don't apply.
Few would dispute heavy drinking is bad for the health, and that includes a raised risk of certain cancers. However, there is a long-running debate as to whether even the occasional tipple comes with an increased risk compared to not drinking at all. An alternative theory proposes a “u-shaped” graph for many health risks, with moderate drinkers having lower risks than either heavy drinkers or complete abstainers.
Numerous studies over the years have produced conflicting results on this question, partly because there are so many confounding factors. People who don't drink aren't a random subset of the population and often differ from moderate drinkers in other ways that may affect their risk. Dr Pek Kei Im of Oxford Population Health and co-authors chose to look at a specific group of non-drinkers who are likely to have fewer confounding factors, and reports in International Journal of Cancer they reap the benefit.
Overall, male non-drinkers have a 14 percent lower risk of getting cancer, the study found, and a 31 percent reduced risk of specific cancers previous studies have linked to alcohol, such as colon, esophagus, and liver.
Most people who don't drink do so for religious reasons or because they or someone close to them previously struggled with addiction. Their inclusion in studies, particularly people who once had a drinking problem, can interfere with comparisons. Consequently, the team looked at a sample of Chinese people who have a genetic intolerance for alcohol, figuring they were less likely to differ from the general population in factors such as diet.
Two gene variants (alleles) common in East Asia interfere with the production of enzymes that detoxify alcohol, causing acetaldehyde to build up in the blood after drinking. Most people with these genes find alcohol consumption less pleasant than the rest of the population, and so do it rarely or not at all. For the few who drink anyway, acetaldehyde, a known carcinogen, is suspected to add to their risk.
Im and co-authors looked for the ALDH2 and ADH1B alleles in DNA from 150,000 people deposited in the China Kadoorie Biobank and compared these with responses to questions about drinking habits and 11 years of health insurance records.
Only 1 percent of men with one allele of the ALDH2 gene in the study drank regularly, compared to 46 percent of those with a different allele, and their cancer rates were correspondingly lower. However, it appears that for those lacking the alcohol-destroying enzymes, acetaldehyde increases their risk of cancer relative to other drinkers. With so few drinkers among those with the relevant alleles, this observation is more tentative.
“These findings indicate that alcohol directly causes several types of cancer, and that these risks may be increased further in people with inherited low alcohol tolerability who cannot properly metabolise alcohol,” Im said in an emailed statement.
Alcohol consumption is so low among Chinese women (only 2 percent reported drinking regularly), that even though they made up 60 percent of the sample, the analysis focused on men instead. But they did find that low-alcohol tolerability alleles were not linked to increased risk of cancer in women, indicating that the reduced risk of cancer in men carrying these gene variants directly results from their lower alcohol consumption.
One comfort in this for those fond of alcohol is that the effects in moderation are modest, which is why we have taken so long to confirm them.