Multiple Sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system.
MS produces a loss of myelin in multiple areas of the brain.
Causes are still unknown, genesis of the disease seems to be caused by a combination of environmental and genetic factors, about 2.5 million people worldwide are afflicted with this disease, women are more affected than men (Two MS sufferers on three are women).
A study of Boston’s Harvard T.H. Chan School of Public Health, in collaboration with the Finnish University of Turku, found that women with low levels of vitamin D aret more likely to develop multiple sclerosis.  For the study, researchers had 800 samples of finnish womens available as part of prenatal testing.
The study obviously needs further research and probably can not be applied to all populations as it is only tested on predominantly white women (for example results may not be applicable to men or people with different ethnic backgrounds), but it may prove that vitamin D deficiency can be an important factor in identifying the disease.