Sunlight in Youth: Protective for MS?

W. James Gauderman, Ph.D., Wendy Cozen, DO, M.P.H., and Thomas M. Mack, M.D., M.P.H.
University of Southern California
NIEHS Grant P30ES007048

Members of the Southern California Environmental Health Sciences Center funded by NIEHS report in the July edition of the journal Neurology evidence from a study of identical twins that exposure to sunlight through various activities at an early age may be protective against developing multiple sclerosis (MS). This study adds to the growing body of evidence that sunlight acting directly through an unknown mechanism or indirectly through stimulation of vitamin D production plays a role in preventing the development of multiple sclerosis as an adult.

The study assessed sun exposure of 79 pairs of identical twins in the US and Canada. One twin in each pair had been diagnosed with MS. Study participants were questioned about a variety of exposures including the amount of time spent tanning, going to the beach, and playing outdoor sports during childhood. The researchers found that the twin with MS usually had been exposed to less sun overall as a child than the twin without the disease. However, the protective effect was only found in female twins. According to the researchers, the lack of a protective effect in males may be due to a relatively small number of male twins in their study.

MS is an autoimmune disorder of the nervous system. There are currently more than 400,000 Americans living with the disease and approximately 2½ million people worldwide. MS is progressive and has no known cure; it is unclear what actually causes MS, but it is characterized by a loss of the protective myelin covering of the brain and the nerves of the central nervous system.

While the harmful effects of the sun to the skin and eyes are well documented, if the current results are replicated, sun exposure would be a simple way to combat MS in the children of parents with the disease—a known high-risk group. The chance that a child of a parent with MS will also develop the disease is much greater than in the general population.

Citation: Islam T, Gauderman WJ, Cozen W, Mack TM. Childhood sun exposure influences risk of multiple sclerosis in monozygotic twins. Neurology. 2007 Jul 24;69(4):381-8.