After our MS Research Day on the 30th January we have been asked by several people about the correct dose of vitamin D to take to try and prevent MS and related disorders. Unfortunately we don't know. Until we do the appropriate clinical trials any recommendations will not be evidence-based. At present we defer to the Vitamin D Council's recommendations (www.vitamindcouncil.org):
".... if you have little UVB exposure, my advice is as follows: healthy children under the age of 1 years should take 1,000 IU per day—over the age of 1, 1,000 IU per every 25 pounds of body weight per day. Well adults and adolescents should take 5,000 IU per day....."
Before starting vD supplementation at this level we would urge you to see your doctor to discuss things formally; ideally this should be done in conjunction with blood monitoring.