A bacterium that causes ulcers and cancers of the stomach seems to have a beneficial side - it significantly decreases the risk of one specific type of oesophageal cancer - reveals an Australian study.

The bacterium, Helicobacter pylori (H. Pylori) is present in nearly fifty per cent of the world's population, and it is a known cause of stomach cancers and ulcers.

Improved sanitation and antibiotics have caused the bacteria to be less common and as a result, have cut down the incidence of stomach cancers and ulcers.

However, Dr David Whiteman of the Queensland Institute of Medical Research (QIMR) said the bacteria might be considered an unusual candidate for protection against gasto-intestinal disease.

We know that H. pylori infection causes gastritis, stomach ulcers and cancers of the stomach, so it might seem odd to propose that this germ could also have benefits, said Dr Whiteman.

Previous research has suggested that H. pylori may actually reduce the risk of oesophageal cancer, but little was known about how it did so.

A study involving analyzed blood samples from more than 2,000 Australians - 800 with oesophageal cancer and 1,400 without - in an effort to examine if they had H. Pylori antibodies in their blood, and whether they carried certain genes thought to determine a person's reaction towards the bacteria, revealed something positive about H. Pylori.

We found that patients with one particular type of oesophageal cancer - adenocarcinomas - were less than half as likely to be infected with H. pylori than people without cancer, whereas patients with squamous cell cancers had a similar rate of infection as people without cancer, said Dr Whiteman.

In other words, H. pylori infection appeared to reduce the risk of adenocarcinoma by more than 50 per cent.

Though researchers expected the protective benefits of the bacterial infection might be limited to people with certain genes that modulate inflammation, they found the risk reduction was similar no matter what genes the person carried.

We now need to understand how this bacterium reduces the risk of adenocarcinoma of the oesophagus. We have some theories, said Dr Whiteman and colleagues.

H. pylori bacterium has coexisted with humans for so long and despite its potential effect in causing cancers and ulcers of the stomach may have some positive role in protecting people from oesophageal adenocarcinomas.