Although the risk of multiple sclerosis (MS) is often blamed on genetics, there are significant geographic variations in MS frequency, which suggests strong environmental factors may be at play.
One such factor is sunlight exposure and vitamin D. MS is rare in Asia, the tropics and the sub-tropics, and strong correlations exist between MS, location, and duration and intensity of sunlight.
In short, sunlight exposure has been linked to a reduced risk of MS, and vitamin D deficiency (caused by a lack of sun exposure) has been suggested as a cause of MS.
A review of epidemiological studies found a protective role of vitamin D for MS. Meanwhile, animal studies have found that an injection of vitamin D3 can prevent experimental autoimmune encephalomyelitis (EAE), which is an animal model of MS. Vitamin D deficiency accelerated the onset of EAE in animals.
The researchers concluded that vitamin D supplementation, at levels higher than are currently recommended by the Institute of Medicine, may help to reduce the risk of MS.
Other environmental factors that may also increase the risk of MS include infection with the Epstein-Barr virus and cigarette smoking.