title: Vitamin D in ankylosing spondylitis: review and meta-analysis.
abstract: 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).
  
  
  CONCLUSIONS
  The higher levels of serum vitamin D were associated with a decreased risk of AS, and showed an inverse relationship with AS activity.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Guoqi
authors.initials: G
authors.lastname: Cai
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Dazhi
authors.initials: D
authors.lastname: Fan
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Lihong
authors.initials: L
authors.lastname: Xin
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Yanting
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Ding
authors.affiliation: Department of Rheumatism and Immunity, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, China.
authors.forename: Shengqian
authors.initials: S
authors.lastname: Xu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Guo
authors.initials: G
authors.lastname: Xia
authors.affiliation: Menzies Research Institute Tasmania, University of Tasmania, Private Bag 23, Hobart, TAS 7000, Australia.
authors.forename: Xingzhong
authors.initials: X
authors.lastname: Jin
authors.affiliation: Department of Rheumatism and Immunity, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, China.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China.
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Zou
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, 81 Meishan Road, Hefei, Anhui 230032, China. Electronic address: famingpan@ahmu.edu.cn.
authors.forename: Faming
authors.initials: F
authors.lastname: Pan
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism; D002112:Calcifediol / Q000097:blood*; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood; D016022:Case-Control Studies; D004198:Disease Susceptibility; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000097:blood* / Q000175:diagnosis / Q000473:pathology
chemical_list: D010281:Parathyroid Hormone; D002097:C-Reactive Protein; D000469:Alkaline Phosphatase; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium
keywords: Alkaline phosphatase; Ankylosing spondylitis; Disease activity; Meta-analysis; Serum vitamin D; Systemic inflammation