Ratanaphisit T.Sukharomana M.Piyaphanee N.Tangcheewinsirikul S.Charuvanij S.Mahidol University2026-05-272026-05-272026-05-15European Journal of Pediatrics Vol.185 No.6 (2026)https://repository.li.mahidol.ac.th/handle/123456789/116942This study aimed to determine the prevalence of vitamin D deficiency and identify its associated factors in patients with newly diagnosed childhood-onset systemic lupus erythematosus (c-SLE). This retrospective study included patients with c-SLE aged ≤ 18 years treated at an academic tertiary center between January 2013 and December 2023. Vitamin D deficiency was defined as a serum 25-hydroxyvitamin D (25-OHD) level < 20 ng/mL. A total of 192 patients with c-SLE were included (87% female; mean [SD] age, 12.1 [3.0] years). Lupus nephritis (LN) was identified in 92 patients (48.2%). The median serum 25-OHD level was 15 ng/mL (IQR, 11.2-22.8), and vitamin D deficiency was identified in 126 patients (65.6%). Compared to those without vitamin D deficiency, deficient patients were older and had higher body mass index, more frequent LN, and higher urine protein-to-creatinine ratio (UPCR; P < 0.05). These patients also had lower estimated glomerular filtration rate and serum complement 3 levels (P < 0.05). Serum 25-OHD levels were negatively correlated with UPCR (ρ =  - 0.38, P < 0.001). On multivariable logistic regression, increased UPCR was independently associated with vitamin D deficiency (adjusted odds ratio, 1.54; 95% CI, 1.15-2.24; P = 0.011). Patients with moderate (SLEDAI-2 K, 7-12) and high disease activity (SLEDAI-2 K ≥ 13) had a higher prevalence of vitamin D deficiency (P = 0.002 and P < 0.001, respectively). CONCLUSION: Vitamin D deficiency was prevalent in newly diagnosed c-SLE and was associated with LN, proteinuria, and moderate to high disease activity. WHAT IS KNOWN: • Childhood-onset systemic lupus erythematosus (c-SLE) is a complex autoimmune connective tissue disease in which vitamin D has been implicated in immune dysregulation. WHAT IS NEW: • Vitamin D deficiency was identified in 65.6% of newly diagnosed Southeast Asian c-SLE. • c-SLE patients with LN had a higher prevalence of vitamin D deficiency than those without LN, particularly those with proteinuria.MedicineArticleSCOPUS10.1007/s00431-026-07066-32-s2.0-1050393215101432107642141164