Background Although vitamin D concentration is reportedly associated with the pathogenesis and pathology of systemic lupus erythematosus (SLE), benefits of vitamin D supplementation in SLE patients have not been elucidated, to our knowledge. We investigated the clinical impacts of vitamin D supplementation in SLE. Methods A cross-sectional analysis was performed using data from a lupus registry of nationwide institutions. We evaluated vitamin D supplementation status associated with diseaserelated Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) as a parameter of long-term disease activity control. Results Of the enrolled 870 patients (mean age: 45 years, mean disease duration: 153 months), 426 (49%) received vitamin D supplementation. Patients with vitamin D supplementation were younger (43.2 vs 47.5 years, P 0.0001), received higher doses of prednisolone (7.6 vs 6.8 mg/day, P = 0.002), and showed higher estimated glomerular filtration rates (79.3 vs 75.3 mL/min/1.73m2, P = 0.02) than those without supplementation. Disease-related SDI (0.73 ± 1.12 vs 0.73 ± 1.10, P = 0.75), total SDI, and SLE Disease Activity Index (SLEDAI) did not significantly differ between patients receiving and not receiving vitamin D supplementation. Even after excluding 136 patients who were highly recommended vitamin D supplementation (with age 75 years, history of bone fracture or avascular necrosis, denosumab use, and end-stage renal failure), disease-related SDI, total SDI, and SLEDAI did not significantly differ between the two groups. Conclusions Even with a possible Vitamin D deficiency and a high risk of bone fractures in SLE patients, only half of our cohort received its supplementation. The effect of vitamin D supplementation for disease activity control was not observed.
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