Association of seasonal serum 25-hydroxyvitamin D levels with disability and relapses in relapsing-remitting multiple sclerosis.

Background/objectives: The aim of this study was to evaluate the association of serum 25-hydroxyvitamin D (25(OH)D) with disability and frequency of relapses in relapsing-remitting multiple sclerosis (MS) patients.

Subjects/methods: The study included 184 patients with relapsing-remitting MS who were receiving immune-modulating drugs and no vitamin D supplementation. The concentration of 25(OH)D was measured in February and August 2014. The level of disability was assessed twice according to the Expanded Disability Status Scale (EDSS). The patients were divided into two groups: EDSS 0.0-2 and 2.5-4. The control group comprised 58 age- and sex-matched healthy subjects. The 25(OH)D levels were compared with the occurrence of relapses and the level of disability.

Results: Mean serum 25(OH)D concentrations were significantly lower in winter in both MS patients and controls. Winter level of 25(OH)D was significantly lower in severe MS cases (EDSS 2.5-4.0) than in mild cases (EDSS 0.0-2.0) (P=0.022), and in the controls (P=0.008), especially in females (r=0.38, P=0.0015). Logistic regression analysis showed the winter serum 25(OH)D was significantly associated with MS (odds ratio 0.925; 95% confidence interval, 0.822-0.970). Serum 25(OH)D levels were significantly lower in MS patients with relapses than in those without relapses both in winter, and in summer.

Conclusions: Hypovitaminosis D was more prevalent during winter than summer, both in the sample group and the control, especially in female MS patients with higher levels of disability. Low vitamin D levels are associated with a more severe course of disease and an increased number of relapses.