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.