The genes that regulate how quickly people get drunk also influence their risks of developing cancer of the mouth, larynx or gullet, a new study has found.

People with a fast-acting variant of the gene for alcohol dehydrogenase - the enzyme that breaks down alcohol - were at much lower risk of these cancers, according to scientists collaborating in the international study.

The reason, they conclude in Nature Genetics, is that these hyper-active enzymes break down alcohol, which is a toxin, more quickly.

This means that the mouth and throat are exposed to the damaging effects of alcohol for a shorter period, with a lower chance that cancer will be initiated. The study was led by Paul Brennan of the University of Aberdeen and incorporated data from almost 4,000 cases of cancer and more than 5,000 healthy people from Europe and Latin America.

There are known to be many variants of the alcohol dehydrogenase gene, which determine in part how susceptible people are to drinking. Its true purpose is to convert the alcohol created by bacteria in the gut into aldehydes, and then, via another enzyme, into harmless substances.

Since the invention of brewing thousands of years ago, however, the alcohol and aldehyde enzymes have found themselves a much bigger task - detoxifying alcohol drunk for pleasure. Some people who lack the enzyme cannot drink even small amounts without becoming drunk.

The new study looked at the frequency of six variants of the alcohol dehydrogenase gene in the cancer cases and compared it with the frequency of the same six variants in people who had not developed cancer.

It identified two variants that are particularly powerfully protective, called rs1229984 and rs1573496. People with the rs1229984 gene are known to break down alcohol 100 times faster than those without it.

The results showed that both these genes protect against cancer, and are particularly powerful in combination. Those who carrywrites bylineboth genes were 55 per cent less likely to develop any of the cancers studied.

Dr Tatiana Macfarlane, senior lecturer at the University of Aberdeen's department of general practice and primary care, and one of the authors, said: “The study showed that your risk of getting oral cancers is linked to genetics as well as lifestyle.

“We found that, in particular, the risk depends on how fast your body metabolises alcohol.

“The results suggest that the faster you metabolise it, the lower your risk.

“These results provided the strongest evidence yet that alcohol consumption is strongly linked to oral cancers.

“The risk is particularly high if you also smoke or rarely eat fruit and vegetables.”

Professor Gary Macfarlane, chair in epidemiology at the University, said: “At a time when we are concerned about the levels of alcohol consumption in the United Kingdom, these results demonstrate the public health importance of measures to reduce consumption and prevent deaths at young ages from diseases, including oral cancers.”

In healthy people, neither of these gene variants seems to be linked to the amount of alcohol consumed. If possessing these protective genes encouraged people to drink more - because they metabolised alcohol more quickly - then any benefit would be eroded.

But in fact there is no link between the genes and drinking habits. Equally, the genes do not have any effect on cancer risk among non-drinkers.

The only possible conclusion, say the authors, is that the protective effect comes from the greater ability of the carriers of these genes to break down alcohol before it can do so much harm.

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