By Karla Gale
NEW YORK (Reuters Health) Aug 08 - Sun exposure, particularly during childhood and early adolescence, is associated with a reduced risk of multiple sclerosis (MS), Australian researchers report in the British Medical Journal for August 9.
"If true, this would seem to indicate that moderate sun exposure at critical periods in early life may protect against multiple sclerosis," co-author Dr. Terry Dwyer told Reuters Health.
"One of the most striking features of multiple sclerosis is a gradient of increasing prevalence with latitude," Dr. Dwyer and colleagues write. To investigate the possible reasons for this phenomenon, the team interviewed 136 residents of Tasmania diagnosed with MS and 272 age- and sex-matched control subjects.
They observed a strong inverse association between childhood sun exposure during weekends and on holidays and MS, with adjusted odds ratios of 0.52 and 0.63 for winter and summer exposure, respectively, at ages 6 to 10. After controlling for smoking and skin melanin density, the odds ratio for MS was 0.31 for a sun-exposure average 2 to 3 hours or more a day in summer.
Greater level of actinic damage was also a predictor of MS, with an adjusted odds ratio of 0.17 for grade 6 compared with grade 3. However, sun exposure during the 10 years prior to MS was not associated with risk.
It appears that "winter sun exposure might be more important in prevention than summer sun exposure, and that only moderate levels of exposure might be necessary," Dr. Dwyer said. Thus, "our data do not suggest that the public health recommendation to avoid high levels of sun exposure during summer for the purpose of avoiding skin cancer should be changed."
He believes the effect of exposure is related to suppression of T helper 1 cell mediated immune responses by ultraviolet-radiation and vitamin D. The research team is now conducting further studies of the relationship between sun exposure, genetic profiles and MS progression.
BMJ 2003:327:316-320.
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