High doses of vitamin D have been shown in a new study to help the immune systems of multiple sclerosis (MS) sufferers.
MS is a chronic, incurable disease that attacks the central nervous system. Symptoms include numbness in the limbs, difficulty walking, paralysis, vision loss, fatigue, and pain.
The study, published in the Dec. 30, 2015, online edition of Neurology, shows that high doses of vitamin D – 10,400 IU (international units) a day – reduces the proportion of certain immune-system cells that have been implicated in the MS disease process, and thus reduce inflammation.
“I’m not going to make any claims beyond that,” said senior researcher Peter Calabresi, M.D., a professor of neurology at Johns Hopkins University in Baltimore. “We don’t have enough data here to guide clinical practice” 
Bruce Bebo, executive vice president of research for the National Multiple Sclerosis Society, the group that funded the study, said:
“This study was not designed to look at efficacy against MS. It was too small and too short to do that.”
Even so, Bebo said the study provides insight into the link between multiple sclerosis and vitamin D deficiency.
Researchers enlisted 40 people with MS to test the doses of vitamin D. Each person received either a 10,400 IU-dose of vitamin D, or a lower dose of 800 IU. The recommended daily amount is 600 IU.
It was not known until now how many IUs of the vitamin were needed for the benefit. Too much of it increases the amount of calcium in the body, which can result in kidney stones, nausea, and vomiting. 
The team found that the concentration of vitamin D in the blood of the higher dosage patients fell in line with the previously suggested optimum levels for MS sufferers. Translation: These individuals had the maximum amount of vitamin D available to them that will benefit them.
The lower-dose group failed to reach that target, and still had a vitamin D deficiency in their blood.
Dr. Calabresi said:
“These results are exciting, as vitamin D has the potential to be an inexpensive, safe and convenient treatment for people with MS. More research is needed to confirm these findings with larger groups of people and to help us understand the mechanisms for these effects, but the results are promising.”
Calabresi noted that high doses of vitamin D may also benefit people with autoimmune diseases. 
There are a number of clinical trials underway that are testing vitamin D’s effect on people with MS, including a U.S. study that is still recruiting patients. Participants are given doses between 5,000 and 10,000 IUs a day.