could geographic patterns be explained by ambient ultraviolet radiation?
OBJECTIVE: This ecological study describes and quantifies the association between ambient ultraviolet (UV) radiation levels, including daily winter vitamin D effective UV radiation levels and the incidence of the 3 antineutrophil cytoplasmic antibody-associated vasculitides (AAVs): Wegener’s granulomatosis (WG), microscopic polyangiitis (MPA), and Churg-Strauss syndrome (CSS). Latitudinal variation in occurrence of the AAVs, especially WG, has been previously reported. For other autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus, inverse associations with latitude are hypothesized to indicate a causative role for low UV radiation exposure, possibly acting via vitamin D status. METHODS: Published epidemiologic studies provided data on incident cases, total population of study regions, age-specific incidence rates, and study location. From these data and online age-specific population data, we calculated crude incidence rates, the expected number of cases (to con
