Association of Increased Sun Exposure Over the Life-Course with a Reduced Risk of Juvenile Idiopathic Arthritis.

Cutaneous sun exposure is an important determinant of circulating vitamin D. Both sun exposure and vitamin D have been inversely associated with risk of autoimmune disease. In juvenile idiopathic arthritis (JIA), low circulating vitamin D appears common, but disease-related behavioural changes may have influenced sun exposure. We therefore aimed to determine whether pre-disease sun exposure is associated with JIA. Using validated questionnaires, we retrospectively measured sun exposure for 202 Caucasian JIA case-control pairs born in Victoria Australia, matched for birth year and time of recruitment. Measures included maternal sun exposure at 12 weeks of pregnancy, and child sun exposure across the life-course pre-diagnosis. We converted exposure to UVR dose, and looked for case-control differences using logistic regression, adjusting for potential confounders. Higher cumulative pre-diagnosis UVR exposure was associated with reduced risk of JIA, with a clear dose response relationship (trend p=0.04). UVR exposure at 12 weeks of pregnancy was similarly inversely associated with JIA (trend p=0.011). Associations were robust to sensitivity analyses for pre-diagnosis behavioural changes, disease duration, and knowledge of the hypothesis. Our data indicate that lower UVR exposure may increase JIA risk. This may be through decreased circulating vitamin D, but prospective studies are required to confirm this. This article is protected by copyright. All rights reserved.