Effects of vitamin D in clinically isolated syndrome and healthy control participants: A double-blind randomised controlled trial.

Background: Lowserum vitamin D levels are associated with susceptibility to, and severity of, multiple sclerosis. High dose vitamin D has been proposed as a potential immunomodulator in multiple sclerosis.

Objectives: We performed a single centre, investigator-led, exploratory, double-blind, randomised, placebo controlled, trial of vitamin D in clinically isolated syndrome and healthy control participants to assess its immunological effects. Secondary end-points included clinical and magnetic resonance imaging outcomes and safety.

Methods: Clinically isolated syndrome patients and healthy control participants were randomised to: placebo, 5000 IU or 10,000 IU vitamin D/day (Vigantol oil). Study duration was 24 weeks.

Results: The trial did not meet its primary end point, with no difference in the frequency of pro-inflammatory CD4 T cells (interleukin (IL)-17/interferon (IFN)-γ) seen. A higher level of disease freedom (67% versus 50%) was seen in those with serum 1,25 (OH) vitamin D levels>100 nmol/l but this did not reach significance. High dose vitamin D was well tolerated with no safety signal.

Conclusions: High dose vitamin D over 24 weeks was well tolerated but without immunological, magnetic resonance imaging or clinical evidence of benefit. The hypothesised therapeutic effects in clinically isolated syndrome or multiple sclerosis patients may require longer periods of administration or may only be seen in patients treated with vitamin D as an adjunct to established disease modifying therapies.