Peripheral vitamin D levels in ankylosing spondylitis: A systematic review and meta-analysis

OBJECTIVES: Previous studies showed conflicting results regarding peripheral vitamin D levels in ankylosing spondylitis (AS). We performed this systemic review and meta-analysis to explore whether vitamin D may influence AS process. METHODS: Articles published until March 2022 were searched in databases as follows: PubMed, Web of Science, and Google Scholar. The present study included cross-sectional and case-control studies regarding vitamin D levels in patients with AS. Studies were excluded according to the following exclusion criteria: (1) we excluded studies which did not provide sufficient information regarding the comparison of vitamin D levels in AS patients and healthy controls (HC). Vitamin D levels in the two group studies should be reported or could be calculated in included studies; (2) meta-analysis, reviews and case reports. STATA 12.0 software was used to make a meta-analysis. Standard mean differences (SMDs) and 95% confidence intervals (CIs) were computed as effect size. RESULTS: The present meta-analysis showed no significant difference in peripheral 1,25-dihydroxyvitamin D3 (1,25OHD) levels between AS and healthy controls (HCs) in Caucasians with a random effects model [SMD: −0.68, 95% CI (−1.90, 0.54)]. Patients with AS had lower peripheral 25-hydroxyvitamin D (25OHD) levels compared with HC with a random effects model [SMD: −0.45, 95% CI: (−0.70, −0.20)]. Patients with AS had higher peripheral C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) levels compared with HC in Caucasian population with random effects models [CRP: SMD: 1.08, 95% CI: (0.78, 1.37); ESR: SMD: 0.86, 95% CI: (0.39, 1.34)]. However, no significant difference in alkaline phosphatase (ALP), parathyroid hormone (PTH) or calcium levels were indicated between AS and HC in Caucasian with random effects models [ALP: SMD: 0.07, 95% CI: (−0.41, 0.55); PTH: SMD: −0.15, 95% CI: (−0.56, 0.26); calcium: SMD: −0.06, 95% CI: (−0.39, 0.26)]. CONCLUSION: In conclusion, the study showed an inverse association between 25OHD and AS, which suggests that vitamin D may have a protective effect on AS. ESR and C-reactive protein (CRP) are important biomarkers for AS.