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Explaining multiple sclerosis prevalence by ultraviolet exposure: a geospatial analysis

Background Epidemiologic studies have shown a positive correlation of multiple sclerosis (MS) prevalence with latitude. However, there has not been a causal association found. Increased dietary intake and increased serum levels of vitamin D showed to be protective for the development of MS. Ultraviolet (UV) radiation plays an important role in vitamin D synthesis and could potentially explain both latitude differences in MS prevalence and the low levels of vitamin D in individuals with MS. Objective To evaluate the relationship between UV radiation and MS prevalence using geospatial analysis. Methods Geospatial analysis was performed on North American regions and separately for the continental United States. The correlation of UV radiation (measured as UV index [UVI]) versus MS prevalence and UV radiation versus case-control ratios was calculated. In addition, the relative risk (RR) of MS was determined for regions/states with low UV radiation exposure. Results Case-control ratios by US state and MS prevalence by North American region showed a strong negative (inverse) correlation with UVI (R = −0.72 and −0.86, respectively). The RR for the five highest risk states/lowest UVI versus the five lowest risk states/highest UVI was increased (RR = 1.8–5.4). The RR for MS, when comparing North American regions with lowest and highest UVI, was 3.78 and within US regions was 1.52. Conclusion This analysis suggests a strong association between UV radiation and MS distribution, and an increase in risk for MS in those areas with a low UVI.