Nature chats with a few researchers about something that’s been known for more than 30 years but is still not really widely accepted – that there’s a demonstrated link between drinking alcohol and cancer:
Scientists first labelled alcohol as a carcinogen more than 35 years ago, and the evidence has only grown since. “I don’t think the relationship between alcohol and certain cancers is terribly controversial,” says Tim Naimi, an alcohol epidemiologist at the University of Victoria, Canada.
What has been less clear is the level of drinking at which cancer risk starts to rise, and how to weigh that elevated risk against alcohol’s other impacts — in particular, the fiercely debated claim that low or moderate drinking improves heart health for some people. “Drinking a lot is absolutely bad,” says Emmanuela Gakidou, who analyses alcohol risks at the Institute for Health Metrics and Evaluation in Seattle, Washington. “It’s the low-to-moderate amount of alcohol where the debate is.”
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Other evidence comes from animal experiments and from laboratory studies that have identified mechanisms by which alcohol can cause cancer. The most well-established is that ethanol is broken down into acetaldehyde, a toxin that damages DNA.
Scientists like to look at the sum of evidence, and there are two syntheses of research that are considered particularly definitive for alcohol and cancer. One is from the International Agency for Research on Cancer (IARC), the World Health Organization’s cancer branch. The agency classed drinking alcohol as carcinogenic to humans in 1988 — putting it in the same category as tobacco smoke and asbestos — and restated that view3 in 2007.
The other synthesis is from the Global Cancer Update Programme, a continuing effort to assess the totality of evidence on links between cancer, physical activity, body weight and diet (including alcohol) using systematic reviews and a panel of specialists to assess the strength of the evidence. The programme’s most recent report4, in 2018, concluded that there is strong evidence that alcoholic drinks increase the risk of several cancers.
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On the basis of such syntheses, researchers agree that alcohol increases the risk of at least seven types of cancer: mouth, throat (pharynx), voice box (larynx), oesophagus, breast cancer in women, colorectal and liver. Scientists suspect that other cancer types will be added as more data are collected.
Studies present this risk in different ways. One complication is that, in alcohol studies and guidelines, the amount of alcohol in a ‘standard’ drink differs between countries: a standard drink in the United States contains 14 grams of ethanol, in Canada it holds 13.45 g, in Australia 10 g and the in United Kingdom 8 g.
In the surgeon general’s report, the results from a large cohort study5 led by Sarich were used to calculate the absolute risks of developing any of the seven cancer types above (see ‘Cancer risk goes up’). This showed that around 17 out of 100 women who drink either nothing or less than one standard US drink per week (14 g ethanol) would develop such a cancer in their lifetime. This was taken as the baseline level of risk. This number rose to nearly 22 out of 100 in women who have two drinks per day (28 g ethanol) on average. Therefore, five more women would develop cancer owing to the higher level of alcohol consumption.