Vitamin D in MS: a vitamin for 4 seasons.

OBJECTIVE: There is increasing evidence that vitamin D can be protective against the development of multiple sclerosis (MS), but it may also be beneficial for the clinical course of the disease. Our objective was to prospectively investigate if 25-hydroxy-vitamin D (25OH-D) levels are associated with exacerbation risk in MS in a study with frequent serum measurements. METHODS: This was a prospective longitudinal study in 73 patients with relapsing-remitting MS. Blood samples for 25-OH-D measurements were taken every 8 weeks. Associations between 25-OH-D levels and exacerbation rates were assessed using Poisson regression (generalized estimating equations) with the individual serum levels as time-dependent variable.