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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 serumvitamin D,parathyroid hormone(PTH),serumcalciumand 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 Creactive 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 b 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 ALPwas associatedwith 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.