Vitamin D levels in systemic sclerosis patients: a meta-analysis

Purpose: This study aimed to investigate the association between vitamin D and systemic sclerosis (SSc) by meta-analysis. Methods: A comprehensive search was performed through June 12, 2017. Pooled standardized mean difference (SMD) was used to estimate the mean vitamin D difference between case and control groups (or between diffused-and limited-type SSc). Pooled risk ratios (RRs) with 95% confidence intervals (CIs) were used to assess the impact of vitamin D level on clinical characteristics of SSc patients. All statistical analyses were performed using Revman 5.0 software. Results: The search yielded six studies with a total of 554 SSc patients and 321 healthy controls. The meta-analysis showed that SSc patients suffered from decreased vitamin D levels (SMD =-8.72 ng/mL; 95% CI: -10.11 to -7.32) compared with healthy controls. The meta-analysis results of three studies with 240 SSc patients (93 diffused-type and 147 limitedtype SSc patients) showed that diffused-type SSc patients exhibited lower vitamin D levels (SMD =-4.71 ng/mL; 95% CI: -8.98 to -0.44) compared with limited-type SSc patients. However, vitamin D level was not found to be associated with Rodnan score (SMD =-2.29 ng/mL, 95% CI: -8.49 to 3.91, P= 0.47), systolic pulmonary pressure (SMD =-1.68 ng/mL, 95% CI: -10.79 to 7.43, P= 0.72), gastrointestinal ulcer (RR = 1.01, 95% CI: 0.53-1.93, P= 0.98), or pulmonary involvement (RR = 1.01, 95% CI: 0.36-2.86, P= 0.99) in SSc patients. Conclusion: SSc patients exhibited lower vitamin D levels compared with healthy controls. Vitamin D levels in diffused-type SSc patients were significantly lower than those in limitedtype SSc patients. The severity of clinical features was not associated with the extent of vitamin D deficit. Therefore, we hypothesize that SSc patients, especially diffused type, have lower vitamin D levels, and that the decrease of vitamin D levels might not be an accelerating factor of SSc severity.