Evidence for a treatment effect of vitamin D in modifying the course of MS is less compelling than evidence of a preventive effect.
• There is a latitudinal link between MS and vitamin D. The notion that vitamin D was involved in MS etiology was originally proposed to explain the geographical distribution of MS. MS prevalence increases with increasing latitude and decreasing ultraviolet (UV) radiation exposure. The hypothesis gained credibility after immunomodulatory effects of vitamin D were discovered. Further studies showed that patients with MS have lower levels of circulating vitamin D than healthy controls.1 However, this does not prove whether vitamin D deficiency is a causal risk factor for MS or merely a consequence of having a debilitating disease.
• There is also a longitudinal link between MS and vitamin D level. Only 1 longitudinal study measured serum vitamin D levels in individuals before the onset of MS.2 That study showed that those with high levels of vitamin D (>100 nmol/L of 25-hydroxyvitamin D) had a 62% lower risk of MS. This study provides perhaps the strongest evidence to date supporting a causal role for vitamin D deficiency on MS risk.
• Boosting recommended vitamin D levels for the general population could reduce the prevalence of MS, but the risks of doing so are uncertain. The longitudinal study2 suggests that a large proportion of MS cases could be prevented by increasing serum 25-hydroxyvitamin D concentration in the general population to above 100 nmol/L. Because vitamin D deficiency is endemic worldwide, individuals would need to take approximately 4000 IU of vitamin D daily-higher than current recommended daily amounts-to achieve this goal. Although these doses are largely considered to be safe, confirmation of safety and efficacy in a large randomized trial is needed.
• Vitamin D supplementation may be a good strategy for patients with existing MS. Evidence for a treatment effect of vitamin D in modifying the course of MS is less compelling than evidence of a preventive effect. We await the data from adequately powered randomized controlled trials to assess the effect of vitamin D on relapse rate and disability. However, patients may benefit from vitamin D supplementation for prevention of osteoporosis and fractures.
1. Correale J, Ysrraelit MC, Gaitan MI. Immunomodulatory effects of vitamin D in multiple sclerosis. Brain. 2009;132(Pt 5):1146-1160. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19321461
2. Munger KL, Levin LI, Hollis BW, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA. 2006;296:2832-2938. Available at: http://www.ncbi.nlm.nih.gov/pubmed/17179460