Serum vitamin D level correlates with disease activity and health-related quality of life in antineutrophil cytoplasmic antibody-associated vasculitis.

BACKGROUND AND OBJECTIVE: The association between vitamin D levels and disease activity has been established in patients with several autoimmune rheumatic diseases. We aimed to examine the association between vitamin D and disease activity of antineutrophil cytoplasmic antibody-associated vasculitis (AAV). METHODS: Fifty-four AAV patients and 50 age- and sex-matched healthy controls without vitamin D supplements were included. Clinical and laboratory data were evaluated during the assessment of vitamin D levels. Two different forms of vitamin D in the sera-25(OH)D, which is the sum of 25(OH)D2 and 25(OH)D3, and 25(OH)D3, which only includes 25(OH)D in its D3 form-were measured, and the relationship between vitamin D and the obtained data was assessed. Variations in vitamin D levels relative to the season were also evaluated. RESULTS: Patients with AAV demonstrated considerably lower 25(OH)D serum levels than healthy controls (16.0 vs. 20.4 ng/mL, p = 0.016), and the proportion of individuals with vitamin D deficiency was higher in patients with AAV than in healthy controls (68.5% vs. 48.0%, p = 0.035). Both serum 25(OH)D and 25(OH)D3 were positively associated with the 36-item Short-form Health Survey (SF-36) physical component summary and SF-36 mental component summary (MCS) scores. A negative correlation was observed between 25(OH)D and 25(OH)D3 serum levels and Birmingham vasculitis activity score (BVAS), C­reactive protein (CRP), and white blood cell count. Linear regression analysis indicated haemoglobin and 25(OH)D levels to be independently associated with BVAS and CRP and 25(OH)D levels with SF-36 MCS score. No seasonal variations were observed in vitamin D levels. CONCLUSION: The results from this study suggest that vitamin D levels could provide clinically useful information in AAV.