Abstract
Objectives This study aimed to investigate the association between latitude of residence, ultraviolet B radiation exposure (UVB) and MS severity.
Methods This observational study used MSBase registry data. Included patients met the 2005 or 2010 McDonald diagnostic criteria for MS and had a minimum dataset recorded in the registry. The latitude of each study centre and cumulative annualized UVB dose at study centre (from NASA’s Total Ozone Mapping Spectrometer) at ages 6, 18 and the year of disability assessment were calculated. Disease severity was quantified with MS Severity Score (MSSS). Quadratic regression was used to model associations between latitude, UVB and MSSS.
Results 46,128 patients contributing 453,208 visits and a cumulative follow-up of 351,196 patient-years (70% women, mean age 39.2±12, resident between latitudes 19°35´-56°16´) were included. Latitude showed a non-linear association with MS severity. In latitudes >40°, more severe disease was associated with higher latitudes (β=0.08, 95%CI: 0.04–0.12). This would translate into a mean difference of 1.3 MSSS points between patients living in Madrid and Copenhagen. No such association was observed in latitudes <40° (β=-0.02, 95% CI:-0.06–0.03). The overall disability accrual was faster in those with a lower estimated UVB exposure before the age of 6 (β=- 0.5, 95% CI: -0.6–0.4) and 18 years (β=- 0.6, 95%CI:-0.7–0.4), as well as with lower life-time UVB exposure at the time of disability assessment (β=-1.0, 95%CI:-1.1–0.9).
Conclusion In temperate zones, MS severity is associated with latitude. This association is mainly, but not exclusively, driven by UVB exposure contributing to MS susceptibility and severity.
