Teachers are 13 per cent more likely than other professionals to die from autoimmune diseases such as multiple sclerosis, rheumatoid arthritis and lupus, according to American researchers.

Stephen Walsh and Laurie De Chello at the University of Connecticut, United States, looked at the death certificates of more than 860,000 Americans in professional occupations.

Secondary school teachers aged between 35 and 44 were particularly vulnerable: their death certificates were 143 per cent more likely to state an autoimmune disease as the cause of death. The findings, published in the Journal of Rheumatology (vol 27, p 1537), also show that secondary teachers are at greater risk than infant school teachers to die of such a disease .

Mr Walsh pointed out that though the cause of multiple sclerosis is still a mystery, there is a body of research that links it with the Epstein-Barr virus, a member of the herpes family, which secondary students are more likely to be infected with than younger children.

Rheumatoid arthritis is known to be triggered by infection with the bacterium Streptococcus A, and some doctors treat the disease with antibiotics.

The researchers believe that teachers’ relatively high exposure to a large number of children with a range of viruses might explain teachers’ higher incidence of death from an autoimmune disease.

Health surveys have shown that teaching in an urban area is the most stressful of all occupations - more so than being a policeman or fire-fighter.

One in five Americans - 50 million - suffer from auto-immune diseases, with women more susceptible than men.

However, this has been taken into account by the research methods which were weighted to take account of differences in the distribution of age, sex and race between teachers and other professionals.