The British habit of occasional alcoholic binges may be healthier than the French habit of continuous low-level drinking when it comes to preventing oesophagal cancer.

The Biochemical Society heard this week how a theory explaining why frequently drinking alcohol causes oesophagal cancer has been strengthened by new evidence from scientists at University College London.

Oesophagal cancer has a poor prognosis, with only 5 per cent of sufferers still alive five years after diagnosis. Surveys have shown that it is more common among populations where alcohol is drunk frequently, such as France. In the United Kingdom it is more common in Scotland, where alcohol consumption is highest.

Peter Swann, reader in mol-ecular oncology at University College, London, suggested several years ago that alcohol might lead to oesophagal cancer. He suggested that it destroys the body's defences against nitrosamines - which we constantly manufacture in our intestines - from the food we eat.

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Nitrosamines have been shown to cause cancer but they are usually broken down by the liver, through which they must flow before they reach the rest of the body.

Dr Swann showed that half a pint of beer prevents nitrosamines being broken down in the liver, with resulting damage to oesophagal cells when the nitrosamines reached them.

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He thinks that for the nitrosamines to cause the cancer they would have to reach the oesophagus much of the time - and therefore drinking through the day may be more damaging than just in the evening.

But the cancer is also prevalent in places where opium is taken, such as northern Iran.

At the annual meeting of the biochemical society in Leicester this week, Dr Swann said he has shown that morphine, a major component of opium, also prevents the liver detoxifying nitrosamines.

This means that his suggested mechanism could explain the incidence of the cancer in other regions as well. In addition, researchers investigating the high incidence of the cancer in China's Hena province have studied a staple part of the diet - a pickled vegetable similar to silage. They have found that it has a similar effect on nitrosamine breakdown.

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Dr Swann said: "This would be consistent with the hypothesis that human oesophagal cancer is caused by nitrosamines".

Dr Swann's theory is not universally accepted however.

Some scientists believe that oesophagal cancer is more associated with spirits than other types of alcohol; and some think that only certain spirits, such as calvados, contain a substance that leads to cancer.