Suppression of Multiple Sclerosis by Ultraviolet Light

Abstract

The inverse relationship of multiple sclerosis to sunlight exposure was proposed at least 50 years ago but conclusive evidence is unavailable. Since the proposal was made, many researchers have jumped to the conclusion vitamin D mediates this effect. Vitamin D is a pro-hormone produced in the skin by ultraviolet irradiation and/or sun exposure. In addition, an inverse relationship between plasma levels of the vitamin D metabolite, 25(OH)D3, and a reduced incidence of multiple sclerosis has been noted. As a result of the relationship clinical trials have been carried out to determine if vitamin D supplementation can suppress the disease. The results have not supported this idea. In an animal model of multiple sclerosis (experimental autoimmune encephalomyelitis) the vitamin D hypothesis was refuted. Ultraviolet irradiation, on the other hand, consistently reduces the incidence and severity of experimental autoimmune encephalomyelitis. Because experimental autoimmune encephalomyelitis is a widely accepted model of human multiple sclerosis, clinical trials testing the efficacy of the narrow band ultraviolet light in suppression of multiple sclerosis appear warranted. If in fact this narrow band light does suppress human multiple sclerosis, isolation and identification of the compound produced by this light should be initiated.