Abstract: Objective  To comprehensively analyze the effect of vitamin D on asthma and investigate whether vitamin D supplementation reduces acute exacerbation of asthma patients， improves lung function， exhaled nitric oxide fraction (FeNO) and other clinical indicators，to systematically evaluate the safety and efficacy of vitamin D supplementation in asthmatics. Methods  We searched Pubmed，Embase，Medline，CNKI，CBM，VIP and Wanfang Data from database through computer for data as at March 8，2017. All of randomized controlled trials (RCTs) of vitamin D supplementation in patients with asthma were searched， and research literatures included in the RCTs were also traced．Two researchers independently conducted the strict quality evaluation and data extraction for the included studies and made a metaanalysis by using RevMan 5.3 software.Results  Eight trials with a total of  1 026  patients with asthma were pooled in the final study.The metaanalysis showed  the pooled RR of asthma exacerbation was 0.84 (95% confidence interval: 0.501.39)， but there was no significant difference (Z=0.69，P=0.49). FEV1 %  improved (Z=2.40，P=0.02)，and serum 25hydroxyvitamin D significantly increased (Z=4.84，P<0.01).Conclusion  Vitamin D supplementation can improve lung function，increase serum 25hydroxyvitamin D levels，but  can not reduce the number of acute episodes of asthma.

Key words: asthma, vitamin D, metaanalysis