Background: The role of vitamin D in ankylosing spondylitis (AS) is largely unknown. This paper aims to examine the association between serum vitamin D levels and susceptibility and disease activity of AS.

Methods: We searched the relevant literatures in PubMed, Elsevier Science Direct, Chinese Biomedical Database (CBM), Chinese National Knowledge Infrastructure (CNKI) and Wanfang (Chinese) Database published before June 2014. Eight independent case-control studies with a total of 533 AS patients and 478 matching controls were selected into this meta-analysis. Standard mean differences (SMDs) with 95% confidence intervals (CIs) were used to assess the levels of serum vitamin D, parathyroid hormone (PTH), serum calcium and alkaline phosphatase (ALP) in cases and controls, respectively. Correlation coefficients (CORs) have been performed to value the correlationship between vitamin D and disease activity (erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)) of AS patients.

Results: Meta-analysis results suggested that vitamin D may play a protective role in AS (for total vitamin D: SMD = − 0.71, P < 0.001; for 25OHD: SMD = − 0.66, P = 0.002; for 1,25OHD: SMD = − 0.72, P = 0.19). Differences in PTH and serum calcium levels were not significant in AS (SMD = − 0.10, P = 0.67; SMD = 0.12, P = 0.17 respectively), while ALP was associated with AS susceptibility (SMD = 0.20, P = 0.04). The relationship between serum vitamin D levels and disease activity was statistically significant except for 25OHD versus (vs.) CRP or BASDAI (for CRP vs. 25OHD: COR = − 0.22, P = 0.08; for BASDAI vs. 25OHD: COR = − 0.20, P = 0.06, respectively).

Conclusion: The higher levels of serum vitamin D were associated with a decreased risk of AS, and showed an inverse relationship with AS activity.