Vitamin D status and its relationship with systemic lupus erythematosus as a determinant and outcome of disease activity.

Background The importance of vitamin D (VD) in systemic lupus erythematosus (SLE) is being increasingly appreciated, with studies suggesting a relationship between VD deficiency and SLE onset/disease activity. We investigated VD status in SLE patients and its associations with disease activity in a geographical region of India receiving low solar ultraviolet-B (UV-B) index. Materials and methods We enrolled 109 SLE patients along with 109 healthy controls belonging to same ethnicity and localities. Demographic and clinico-laboratory information were recorded. VD status was assessed by estimating serum 25-hydroxyvitamin D (25-OH-D) concentrations (deficient: <20 ng/mL, insufficient: 21-29 ng/mL, and sufficient/normal: ≥30 ng/mL) using an enzyme-linked fluorescent assay (ELFA). The SLE Disease Activity Index (SLEDAI) scoring system was used to evaluate disease activity. The association between VD status and disease activity was assessed by univariate and multivariate approaches. Results Hypovitaminosis D was prevalent in 90.83% SLE patients [vs. 77.98% healthy controls; chi-squared (χ2) = 10.125, df = 2, p < 0.01]. SLEDAI scores and 25-OH-D values were inversely associated, which extended in a two-way manner as revealed by multiple logistic regression models. SLE patients with VD deficiency were more likely to have high/very high disease activity [adjusted odds ratio (OR) = 3.5, 95% confidence intervals (CI): 1.4-8.9]. Conversely, patients with high SLEDAI scores (>10) also had greater risks of being VD deficient (adjusted OR = 3.9, 95% CI: 1.5-10.8). Conclusion VD deficiency is widespread in SLE. The relationship appears to be bidirectional, with VD status associated both as determinant and outcome of disease activity in SLE.