First RCT of Vitamin D supplementation in MS shows no benefit of high dose.

Recently reported in Neurology (and available to the public) this was a small trial of short duration of patients with established MS.  Nevertheless, it shows no benefit, and the direction of effect was towards harm, though it was insignificant.  So, while Vitamin D deficiency appears to be causally related to onset of MS, high-doses of D, which raise blood levels to 40ng or more, don't appear to help.  An interesting "patient page" lays out the strengths and weaknesses of the study.