Some 142 people are believed to have died from vCJD in the UK

Some 142 people are believed to have died from vCJD since it first emerged in the UK nine years ago.

A disproportionate number of these have been young. Some believe this may be because they were more likely to have eaten BSE infected meat.

But French researchers have dismissed the theory, saying it does not explain the relatively high death rates.

Infected meat

They used new figures on the UK population's exposure to BSE-infected meat to estimate how the disease should affect different age groups.

Their computer model suggested that 48% of those with vCJD should be over the age of 40. In reality, only 10% of people affected by the disease are in this age group.

Exposure alone could not explain the young age of vCJD cases Pierre-Yves Boelle

The researchers, from the Assistance Public Hospitals in Paris and University Joseph Fourier in Grenoble, re-jigged their model to consider another risk factor, namely an age-related susceptibility to the disease.

Their theory was that the risks of contracting vCJD increased during childhood, peaked during adolescence and decreased sharply afterwards.

Using this model, they estimated that 12% of those with vCJD should be over the age of 40 - much closer to the actual figure.

While the researchers say further studies are needed, they said the findings showed that simply eating more BSE-infected meat cannot explain relatively high death rates among young people.

"We found that exposure alone could not explain the young age of vCJD cases as seen in the UK," said Pierre-Yves Boelle, one of those involved in the study.

The researchers say more studies are needed to find out why young people may be more susceptible to the disease.

But they suggested that changes in the intestine when children are growing could be one reason.

"One possible explanation for the difference in susceptibility could be that the permeability of the intestinal barrier changes with age," they said.

Frances Hall, of the Human BSE Foundation whose son Peter died from vCJD ten years ago, said: "The vast majority of victims have been very young, which makes it even more awful - these are people on the threshold of life."

The study comes just months after British experts warned that many more people could be infected with vCJD than previously thought.

Researchers at Plymouth's Derriford Hospital and the CJD Surveillance Unit suggested in May that as many as 3,800 Britons may be harbouring the disease.