This study aimed to evaluate the relationship between the level of 25-hydroxyvitamin D [25(OH)D] and systemic lupus erythematosus (SLE). We searched the PUBMED, EMBASE, and Cochrane databases and performed a meta-analysis examining the vitamin D level and/or deficiency in patients with SLE, compared with that in healthy controls. In total, 18 studies consisting of 1,083 patients with SLE and 1,273 controls were included. Vitamin D level was significantly lower in the SLE group than in the control group (standardized mean difference [SMD] = -0.938, 95% CI = -1.352 to -0.524, p = 9.0 × 10-6). Stratification by ethnicity showed a significantly decreased vitamin D level in the SLE group in the European and Arab populations (SMD = -1.485, 95% CI = -2.427 to -0.543, p = 0.002; SMD = -1.067, 95% CI = -1.251 to -0.883, p < 1.0 × 10-8), and an association tendency between decreased vitamin D level and SLE in the Asian population (SMD = -0.874, 95% CI = -2.073 to -0.324, p = 0.153). Subgroup analysis by sample size showed a significantly lower vitamin D level in the SLE group in small- (n ≤ 100) and large-sample (n > 100) populations (SMD = -1.008, 95% CI = -1.672 to -0.344, p = 0.003; SMD = -0.863, 95% CI = -1.444 to -0.293, p = 0.003). Meta-analysis revealed a significant association between SLE and vitamin D deficiency (RR = 2.321, 95% CI = 1.361-3.960, p = 0.002). Stratification by ethnicity showed a significant association between SLE and vitamin D deficiency in European and Arab populations (RR = 2.182, 95% CI = 1.024-4.648, p = 0.043; RR = 4.550, 95% CI = 3.471-5.965, p < 1.0 × 10-8). Our meta-analysis demonstrates that compared with controls, patients with SLE show significantly low serum levels of vitamin D, and that a deficiency of vitamin D is associated with SLE.
Keywords: Deficiency; Systemic lupus erythematosus.; Vitamin D.