When I got diagnosed 10 months ago I was told I had an extremely low Vitamin D level. To be perfectly honest I was shocked since I had lived in San Diego for 10 years (sun all the time) and moved to sunny/hot Texas and have been here the past 4 years. Thus, I'm not sure everyone's bodies can get the Vitamin D they need from the sun -- clearly that wasn't the case for me over the past 14 years and I spend a lot of time outdoors.

I took the 50,000 IU pills once a week for 9 weeks. It bumped my level up into low normal range. I am now taking 1,000 IU a day.

The MS specialist I saw at the Mayo Clinic in MN. said that I should be taking Vitamin D supplements every day. The MS specialist I saw in my own city 2 weeks ago said that Vitamin D deficiency is a risk factor for MS (apparently I hit the MS jackpot and as she put it "the stars lined up" because I had 4 risk factors: 1) Vitamin D deficiency 2) grew up in Mass. until age 22 3) mother just diagnosed with MS last year right before me 4) wicked mono/epstein barr infection the year before my diagnosis).
Lucky me! <heavy sarcasm>

Anyhow, nothing proves that taking Vitamin D after the fact will slow the disease down but why not take the supplement? There does appear to be a correlation of some sort.