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 limited-type 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 limited-type 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.