PAST SUN EXPOSURE, SKIN PHENOTYPE AND RISK OF MULTIPLE SCLEROSIS

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The striking latitudinal gradient of multiple sclerosis (MS) prevalence may reflect variation in ultraviolet radiation (UVR). A Th1 cell mediated attack on myelin proteins appears to be important in the pathogenesis of MS and recent immunological work shows that UVR can suppress the Th1 cell mediated activity. We conducted a population based case-control study in Tasmania, Australia, to examine whether high past sun exposure was associated with a reduced risk of MS. Interviews were conducted with 136 cases with MS and 272 controls randomly drawn from the community and matched on sex and birth year. Measures included reported sun exposure, dermal actinic damage (a marker of cumulative lifetime sun exposure), and skin spectrophotometry. Higher (2.5 hours a day on average) sun exposure in summer on weekends and holidays over the age span of 6–15 years was associated with a decreased risk of MS (adjusted odds ratio, 0.31; 95 percent confidence interval, 0.16 to 0.59). High (grade 4–6) actinic damage was also independently associated with a decreased MS risk (adjusted odds ratio, 0.32; 95 percent confidence interval, 0.11 to 0.88). A dose response relationship was observed in both sun exposure over the age span of 6–15 years (p < 0.01) and actinic damage (p < 0.01). Higher sun exposure appears to be associated with a reduced risk of MS. These findings are consistent with insufficient UVR influencing the development of MS.