Soldiers, sailors and airmen are almost twice as likely to die from multiple sclerosis than other jobs, surprise findings on how the condition affects different occupations have suggested.
Experts on the disease have called for more research, amid speculation the close proximity of military life could help the spread of viruses linked to the debilitating illness.
The Ministry of Defence also said more research was needed after the findings.
Scientists from the Medical Research Council and the Health and Safety Executive looked at the death certificates of nearly 3.7m men stretching over 31 years to examine death rates from MS across job types.
For example, the close proximity in which military recruits live and work might facilitate the transmission of one or more infections that trigger later MS.
Paper in Occupational Medicine
They found data showing men whose last occupation was marked down as Armed Forces were at much greater risk of dying from the incurable neurological disorder.
The research in the journal Occupational Medicine was unable to explain the finding, but concluded it was unlikely to be due to chance and could be due to an “unidentified occupational hazard” from serving in the forces.
The authors found: “Men from the armed forces in England and Wales have experienced elevated proportional mortality from MS in each of three successive decades.
“The consistency and statistical significance of the excess indicate that it is most unlikely to have occurred simply by chance.”
“Moreover, our findings suggest that it cannot be explained entirely by selective exclusion from other employment when leaving the military, by low mortality in servicemen from the most common causes of death or by non-occupational factors related to social class.
“The possibility of an unidentified occupational hazard remains.”
Previous studies from the US have hinted that MS rates could be higher among soldiers who served in the first Gulf War of 1990/91.
But the British survey found relatively consistent rates across three decades.
Around 100,000 people in the UK have the condition, where the immune system attacks the layer surrounding and protecting the nerves.
Symptoms include problems with vision, arm or leg movement, sensation or balance and life expectancy is reduced by an average of seven to nine years.
MS is thought to be caused by both genetic and environmental factors and it has been linked to some infections, particularly those caused by the Epstein-Barr virus responsible for glandular fever).
The authors of the research speculated that “the close proximity in which military recruits live and work might facilitate the transmission of one or more infections that trigger later MS.
“Given the suspicions raised by our analysis, there is a case for analysing data from other military cohorts to check if they support the possibility of an occupational hazard.”
Dr David Schley, from the MS Society, said: “We know different circumstances, such as where you live and work, play a role.
“This research suggests being in the army may increase the risk.
“We welcome more studies to help us understand how we can prevent MS.'
A Ministry of Defence spokesman said: “The causes for MS are complex and can be due to a number of factors.
“As the study itself notes, more research is needed.”