NEW YORK (Reuters Health) – Findings from a new study suggest that exposure to sun during childhood somehow offers protection against multiple sclerosis (MS) later in life.

"Exposure to UV rays may induce protection against MS by alternative mechanisms, either directly by altering the cellular immune response or indirectly by producing immunoactive vitamin D," study authors Dr. Talat Islam and Dr. Thomas Mack, from the University of California in Los Angeles, said in a statement.

According to the report, which appears in the July 24th issue of Neurology, the protective effect seen with sun exposure does not depend on genetic susceptibility to MS.

The findings stem from a comparison of childhood sun exposure in 79 monozygotic twins with one of each pair having MS. The study focused on nine exposure activities, such as suntanning and participation in outdoor team sports.

All nine activities conferred a protective effect against MS, with odds ratios ranging from 0.25 to 0.57. For instance, the twin who spent more time suntanning than the other twin was 60% less likely to develop MS. Spending more time outdoors during the spring seemed to confer the strongest protective effect.

The apparent protective effect was only noted among female twins, Dr. Mack said. However, this may simply be because few male twins were enrolled in the study, he added.

Further research into this topic should now focus on the mechanisms that might explain why sun exposure may cut the risk of MS, the authors conclude.

Neurology 2007;69:381-388.

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