Higher 25‐hydroxyvitamin D is associated with lower relapse risk in multiple sclerosis

Abstract

Objective A protective association between higher vitamin D levels and the onset of multiple sclerosis (MS) has been demonstrated; however, its role in modulating MS clinical course has been little studied. We investigated whether higher levels of serum 25‐hydroxyvitamin D (25‐OH‐D) were associated with a lower risk of relapses in people with MS. Methods We conducted a prospective cohort study of 145 participants with relapsing‐remitting MS from 2002 to 2005. Serum 25‐OH‐D levels were measured biannually, and the hazard of relapse was assessed using survival analysis. Results There was an inverse linear relationship between 25‐OH‐D levels and the hazard of relapse over the subsequent 6 months, with hazard ratio (HR) 0.91 (95% confidence interval [CI]: 0.85–0.97) per 10nmol/l increase in 25‐OH‐D level (p = 0.006). When variation due to timing of blood collection was removed by estimating 25‐OH‐D at the start of each season, this association persisted, with HR 0.90 (95% CI, 0.83–0.98) per 10nmol/l increase (p = 0.016). Taking into account the biological half‐life of 25‐OH‐D, we estimated 25‐OH‐D at monthly intervals, resulting in a slightly enhanced association, with HR 0.88 (95% CI, 0.82–0.95) per 10nmol/l increase (p = 0.001). Adjusting for potential confounders did not alter these findings. Interpretation In this prospective population‐based cohort study, in a cohort largely on immunomodulatory therapy, higher 25‐OH‐D levels were associated with a reduced hazard of relapse. This occurred in a dose‐dependent linear fashion, with each 10nmol/l increase in 25‐OH‐D resulting in up to a 12% reduction in risk of relapse. Clinically, raising 25‐OH‐D levels by 50nmol/l could halve the hazard of a relapse. ANN NEUROL 2010;68:193–203