Multiple Sclerosis is a chronic degenerative disease of the central nervous system in which gradual destruction of myelin occurs in patches throughout the brain or spinal cord (or both), interfering with the nerve pathways and causing muscular weakness, loss of coordination and speech and visual disturbances. It occurs chiefly in young adults and is thought to be a defect in the immune system that may be of genetic or viral origin. It leads to a range of symptoms associated with disruption of nerve function, such as paralysis and tremors. It has been proved that the incidence of multiple sclerosis increases dramatically with latitude, and that exposure to sunlight in childhood and adolescence protects against the disease in later life.
There is a strong circumstantial evidence to prove that vitamin D protects against this disease. It seems that by inhibiting the secretion of melatonin sunlight also prevents multiple sclerosis by strengthening the immune system and preventing demyelization. If the disease is to be avoided, irrespective of the physical mechanism involved, there are good grounds for discouraging children from wearing sunglasses, and encouraging regular moderate sunlight exposure.