Researchers have long known that sun exposure is related to multiple sclerosis. The less sunlight a person is exposed to the greater the risk for this autoimmune disease. Researchers have assumed that there was something about vitamin D made through sun exposure that decreases the likelihood of both developing MS or aggravating the condition. Patients with MS who have low levels of vitamin D tend to have more relapses while those who get high doses of vitamin D appear to be able to stave off these acute episodes.
Now researchers have uncovered a possible mechanism for the vitamin D effect against multiple sclerosis. They have found that vitamin D turns off a gene responsible for generating an immune system compound called Interleukin-17. IL-17 plays a role in the autoimmune system destruction of nerve cells that characterize MS. Vitamin D also turns on a gene that helps T cells combat cell destruction. This combined activity may account for the beneficial effect of this nutrient on MS.
[Molecular and Cellular Biology, Sept., 2011]