Ultraviolet sunlight is too low to produce adequate amounts of vitamin D3, and vitamin D insufficiency lasting 4 to 6 months of the year at latitudes of ≥42° is common in individuals with low vitamin D intake. Vitamin D has strong immunoregulatory effects, and vitamin D supplementation prevents experimental autoimmune encephalomyelitis (EAE), an autoimmune disease in animals that is used as a model of MS.
Recently, emerging data from epidemiologic studies suggest that vitamin D may play an important role in the progression of the development of MS. A longitudinal study in pediatric MS showed a 34% lower risk of relapse for every 10 ng/ml higher 25-hydroxyvitamin D level. A similar magnitude of reduced relapse risk was later reported in an adult MS cohort. Higher vitamin D levels have also been shown to be associated with less subsequent inflammatory MS activity on brain magnetic resonance imaging (MRI). Finally, studies have demonstrated that patients have lower vitamin D levels during MS relapses.
