Scientists have claimed that sun exposure levels account for 61% of the difference between high and low rates of MS across the UK.
The combined effects of a viral infection and lack of ultraviolet rays from the sun are responsible for 72% of variations in MS, the Oxford University researchers said.
It is already recognised that people susceptible to glandular fever - a common infectious illness caused by the Epstein-Barr virus - are more at risk of MS, and a higher incidence pattern was witnessed in those not getting enough sun.
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 the sun.
The scientists, whose findings are reported in the journal Neurology, looked at all admissions to NHS hospitals in England over seven years.