Low levels of sunlight coupled with glandular fever could increase the risk of developing multiple sclerosis (MS), say researchers.
There are many suspected risk factors for MS and the disease is known to be more common away from the equator.
The study, in Neurology, suggested that low levels of sunlight could affect how the body responds to infection.
The MS Society said the study, based on hospital admissions data in England, added weight to existing evidence.
MS affects about 100,000 people in the UK and is more common in the north of England than in the south.
There are also high levels of both vitamin D deficiency and MS in Scotland, where the MS Society is considering carrying out separate research on a possible link between the two. Around 10,500 people have MS in the country, the highest prevalence of the condition in the world.
With MS the protective layer around nerves, known as the myelin sheath, becomes damaged. Messages from the brain to the rest of the body are disrupted, resulting in difficulty moving, muscle weakness and blurred vision.
The researchers at the University of Oxford looked at all hospital admissions in England between 1998 and 2005.
They found 56,681 MS cases and 14,621 cases of glandular fever, which is caused by the Epstein-Barr virus.
The study also used data from Nasa on sunlight intensity.
The researchers found that by just analysing sunlight, they could explain 61% of the variation in the number of MS cases across England.
However when they combined the effect of sunlight and glandular fever, 72% of the variation in MS cases could be explained....
via BBC News - Virus and low sunlight 'raises multiple sclerosis risk'.