Vitamin D, past sun exposure & skin phenotype in risk of central nervous system demyelination

Latitudinal gradients in multiple sclerosis are well described in both northern and southern hemispheres. Previous studies have suggested that sun exposure and/or vitamin D may provide an explanation for the latitudinal gradient. The Ausimmune Study was a multi-centre case control study specifically designed to address this question. Between 1 November 2003 and 31 December 2006, the study recruited 282 cases, aged 18–59 years, with a first clinical diagnosis of central nervous system demyelination (FCD) from four regions of Australia, spanning latitudes of 27° S to 43° S. Controls were matched on age, sex and study region to cases. Data collected included subjective and objective measures of skin type and past sun exposure and vitamin D status (serum 25-hydroxyvitamin D, 25(OH)D). There was a strong latitudinal gradient in FCD incidence. In casecontrol analyses higher levels of past sun exposure or 25(OH)D were associated with lower risk of FCD; these factors in combination explained 22% of the observed latitudinal gradient in FCD incidence.