Can vitamin D supplementation improve symptoms of multiple sclerosis?

Multiple sclerosis (MS) is an autoimmune disease that affects the myelin sheath of neurons, which can be thought of as more or less analogous to the insulation on electrical wires. Degradation of the myelin sheath degrades the ability of neurons to propagate signals back and forth between the body and brain, resulting in MS. There are associations between residing in latitudes further away from the equator and increased risk of MS,^[1] and more sun exposure during childhood is associated with reduced risk of MS during adulthood.^[2]

Vitamin D has been shown to have a therapeutic effect in mice with experimental autoimmune encephalomyelitis, an animal model for MS. However, human trials to date have not found evidence in support of a role for vitamin D supplementation in the treatment of MS.^[3] More research is needed to better understand whether vitamin D supplementation may benefit any particular populations of people with MS.

It is also important to note that some of the side effects of toxicity from high-dose vitamin D supplementation, such as fatigue, muscle weakness and urinary dysfunction, mimic the course of MS disease progression,^[4] underscoring the importance of consulting with a physician before considering aggressive vitamin D supplementation for MS.