Multiple sclerosis may be linked to a combination of a viral infection and a lack of sunlight, research has indicated.
Together the two factors accounted for 72% of variations in the number of MS cases across the UK, researchers from Oxford University found.
Around 61% of the difference between high and low rates of MS could be explained by levels of sunlight exposure alone.
Previous studies have established a link between the development of MS and patients with a history of glandular fever, a common infectious illness caused by the Epstein-Barr virus.
Individuals whose skin is exposed to little sunlight are also found to be more at risk of the condition.
The latest study, published online in the journal Neurology, looked at all admissions to NHS hospitals in England over a period of seven years.
“We wanted to see whether the two together would help explain the variance in the disease across the United Kingdom,” said lead researcher Dr George Ebers, of Oxford University.
MS is an autoimmune disease which destroys myelin, the fatty insulating sheath that surrounds nerve fibres.
Loss of myelin leads to the disruption of nerve signals and symptoms ranging from mild tingling and numbness to paralysis.
Around 100,000 people in the UK suffer from the condition.
Research has shown that MS is more common at higher latitudes away from the equator, where there is less exposure to ultraviolet rays from the sun.
- Ramagopalan SV, et al. Relationship of UV exposure to prevalence of multiple sclerosis in England. Neurology 2011 (76); 1410-1414.