Association between circulating 25-hydroxyvitamin D and systemic lupus erythematosus: A systematic review and meta-analysis.

Aim: The indicators for measuring vitamin D are various, and 25-hydroxyvitamin D (25(OH)D) is considered as the optimal indicator of total vitamin D levels. In this study, we aim to deeply explore the 25(OH)D status in systemic lupus erythematosus (SLE) patients, and evaluate its relation to SLE risk and disease severity.

Methods: Literature about 25(OH)D status and its associations with SLE were searched in Pubmed, Embase and Cochrane Library databases. Standardized mean difference (SMD), odds ratio (OR) and corresponding 95% confidence interval (95% CI) were illustrated by forest plots, and correlation coefficients (r) were combined by generic inverse variance method. Heterogeneity and publication bias were quantified by I-squared (I ) test, funnel plot and Egger's test, respectively. Sensitivity analyses were further examined by leave-one-out method.

Results: Nineteen articles were included into our meta-analysis. The overall results showed that compared with the healthy controls, the circulating 25(OH)D levels were significantly lower in SLE patients (pooled SMD = -1.63, 95% CI: -2.51 to -0.76). Subgroup analysis revealed that compared with the healthy controls, SLE patients of Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) ≥ 10, Arab and European ethnicity, all 4 seasons, no vitamin D supplement, had significantly lower circulating 25(OH)D levels; no significant differences were observed in SLE patients of SLEDAI < 10, mixed ethnicity, spring, summer, vitamin D supplement, respectively; no matter the changes of age, disease duration, and the therapy of corticosteroid or immunosuppressive or neither, circulating 25(OH)D levels were significantly reduced in SLE patients. The deficiency, insufficiency and sufficiency of vitamin D could significantly elevate, slightly decrease (not significantly), significantly decrease SLE risk, respectively (pooled OR = 4.37, 95% CI: 1.49 to 12.84; pooled OR = 0.52, 95% CI: 0.22 to 1.26; pooled OR = 0.31, 95% CI: 0.15 to 0.63). Circulating 25(OH)D levels were inversely associated with SLEDAI (pooled correlation coefficient = -0.50, 95% CI: -0.8278 to -0.1689).

Conclusions: Compared with healthy controls, 25(OH)D levels are significantly lower in SLE patients, which is influenced by disease activity, ethnicity, seasons and vitamin D supplement; no matter the change of age, diseases duration and therapy of corticosteroid or immunosuppressive or neither, 25(OH)D levels are significantly decreased in SLE patients; the deficiency, insufficiency and sufficiency of vitamin D could significantly elevate, slightly decrease, and significantly decrease SLE risk, respectively; and 25(OH)D levels inversely correlate with SLEDAI.