We are certainly not saying people should stop eating vegetables

Prof McColl

Nitrates occur naturally in fruit and vegetables but the use of extra fertilisers began in the 40s when the war effort demanded output was maximised.

Since 1980, permitted levels of nitrate use have decreased over growing health concerns.

Prof McColl and his 10-strong research team have been investigating the link between high levels of nitrate and cancer around the gastro-oesophagael junction, where the oesophagus joins with the stomach.

The team now plans to carry out further tests on humans in a bid to find out the extent of the problem, which appears to affect people in Scotland more than any other part of the UK.

Prof McColl, 51, said: "We are still carrying out this study and are certainly not saying people should stop eating vegetables. But our investigations have shown that there is definitely something happening here.

Human saliva

"Hopefully, with further human tests, we will be able to see exactly how and why this is taking place because at the moment it is a mystery, but one that is having severe consequences."

He revealed that this form of gullet cancer was now more common than stomach cancer in the UK.

The professor also said some victims had been aged as young as 30 and that a number of sufferers died within a few years of being diagnosed.

His team, which has received a �150,000 grant from the Scottish Executive to carry out the study, has found that human saliva plays a vital role in converting nitrates into carcinogens, which come into force at the gastro-oesophageal junction.

And it believes this form of cancer may be prompted in some people at the point when the saliva they swallow first meets the acidic juices in the stomach.

Prof McColl also revealed countries with less sunlight which grow the majority of produce under glass, such as the UK, are more at risk.

The research team is based at Glasgow University

He also said organic food would not prove to be a healthier option because it also contained substantial levels of nitrate, some of which came from natural fertilisers such as manure.

"It appears that the mass production of vegetables in the western world since the last world war may be the underlying factor that has led to such huge increases in this form of cancer," the professor said.

"We now want to determine if the permitted levels of nitrate fertilisers, which has fallen somewhat in recent years, may be partly to blame."

He said research so far had showed that green and root vegetables contained the highest levels of nitrate.

In the last 20 years, the number of people suffering this form of cancer in Scotland alone has risen from 450 to more than 1,100, the professor said.