Association Between Sun Exposure and Risk of Relapse in Pediatric-Onset Multiple Sclerosis.

Background and objectives: Low sun and ultraviolet radiation (UVR) exposures have been associated with increased risk of developing pediatric-onset multiple sclerosis (MS); however, their effect on disease course has not been well characterized. We primarily investigated whether there was an association between time spent in the sun in early childhood and risk of relapse in pediatric MS. We secondarily investigated the effect of sun exposure during more recent periods on risk of relapse.

Methods: We conducted a multicenter cohort study of participants with pediatric-onset MS recruited from 18 pediatric MS clinics across the United States between November 1, 2011, and July 1, 2017. Relapses were identified prospectively after study enrollment; relapses preceding study enrollment were entered retrospectively. Time spent in the sun at various periods of life was measured using a detailed environmental questionnaire, and ambient UVR exposure was determined using zip codes. Multivariable Cox regression models were used to assess the association between time spent in the sun and UVR dose at specific periods of life and the risk of relapse. Models were adjusted for demographic, clinical, and sun exposure-related characteristics.

Results: In our cohort of 334 children with MS, 206 (62%) experienced at least one relapse from disease onset to the end of the follow-up period. After adjustment, ≥30 minutes of daily sun exposure during the first summer of life was associated with a lower risk of relapse compared with <30 minutes (adjusted hazard ratio [aHR] 0.67, CI 0.48-0.92, p = 0.01). Greater time spent in the sun during the second trimester of pregnancy was also associated with reduced risk of relapse (aHR 0.68, CI 0.48-0.97, p = 0.04). UVR dose and time spent in the sun later in life were not significantly associated with relapse risk.

Discussion: In this large cohort study of children with MS, greater early childhood and prenatal sun exposure time was associated with lower risk of relapse. Further investigation of sun exposure at other periods is needed to better characterize its impact on disease course and guide potential future interventions.