Correlation between disease activity of pediatric-onset systemic lupus erythematosus and level of vitamin D in Taiwan: A case–cohort study

Background: Vitamin D deficiency has been associated with systemic lupus erythematosus (SLE), but there is no consensus on the role of serum vitamin D in evaluating or predicting disease activity. This study aimed to demonstrate the direct correlation between vitamin D level and pediatric-onset SLE disease activity by a retrospective cohort study design. Patients and methods: Thirty-five patients with pediatric-onset SLE and paired sera at the active and inactive disease states were enrolled. Disease activity was defined by Systemic Lupus Erythematosus Disease Activity Index 2000, and active lupus nephritis (LN) was defined as active urine sediment, and proteinuria >2+ on stick or >500 mg/day. All data were reviewed and calculated from previous medical records. The levels of both vitamin D2 and vitamin D3 were checked by electrochemiluminescence immunoassay. Results: Serum 25-hydroxyvitamin D (25-OH D) levels in the active status were significantly lower compared to that in inactive disease status (12.0 ± 7.2 ng/mL vs. 15.4 ± 7.4 ng/mL, p = 0.005). A subgroup analysis revealed that at active disease status, patients with LN had lower 25-OH D levels than patients without LN (16.3 ± 8.2 ng/mL vs. 9.8 ± 5.6 ng/mL, p = 0.023). Moreover, there is a significant inverse correlation between serum 25-OH D levels and Systemic Lupus Erythematosus Disease Activity Index 2000 at both inactive (r = −0.335, p = 0.003) and active (r = −0.373, p = 0.016) disease status. Conclusion: Serum vitamin D levels are inversely correlated with SLE disease activity at both active and inactive disease status, and also with the presence of LN at active disease stage.