Abstract
OBJECTIVE: Ultraviolet (UV) radiation exposure is associated with photosensitivity, rashes, and flares in systemic lupus erythematosus (SLE). However, it is not known whether UV exposure increases risk of developing SLE. We examined UV exposure and SLE risk in a large prospective cohort. METHODS: The Nurses' Health Study (NHS) enrolled 121,700 US female nurses in 1976; in 1989, 116,429 nurses were enrolled in NHS II. Biennial questionnaires collected lifestyle and medical data. Self-reported incident SLE by American College of Rheumatology classification criteria was confirmed by medical record review. Ambient UV exposure was estimated by linking geocoded residential addresses with a spatiotemporal UV exposure model. Cox models estimated hazard ratios (HRs) and 95% confidence intervals (95% CIs) across tertiles of time-varying cumulative average UV. We examined SLE risk overall and stratified by anti-Ro/La antibodies and by cutaneous manifestations from 1976 through 2014 (NHS)/2015 (NHS II), adjusting for confounders. RESULTS: With 6,054,665 person-years of exposure, we identified 297 incident SLE cases; the mean ± SD age at diagnosis was 49.8 ± 10.6 years. At diagnosis, 16.8% of women had +anti-Ro/La, and 80% had either +anti-Ro/La or ≥1 cutaneous manifestation. Compared with the lowest UV exposure tertile, risk of overall SLE was increased, but not significantly (HR 1.28 [95%CI 0.96-1.70]). Women in the highest tertile had increased risk of malar rash (HR 1.62 [95% CI 1.04-2.52]). CONCLUSION: Cumulative UV exposure was not associated with SLE risk. Higher UV exposure, however, was associated with increased risk of malar rash at presentation. UV exposure may trigger SLE onset with malar rash among susceptible women.