title: Vitamin D deficiency is associated with the severity of COPD: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To explore the association between host serum 25-hydroxyvitamin D (25(OH)D) and the susceptibility and severity of COPD.
  
  
  METHODS
  Previous studies on the association between host 25(OH)D and the susceptibility and severity of COPD were collected on the basis of a systematic literature search of PubMed and Web of Science up to June 2015. Continuous variable data were presented as standard mean difference (SMD) or weighted mean difference with 95% confidence interval (CI). The dichotomous variable data were analyzed as relative ratio (RR) or odds ratio with 95% CI for cohort and case-control studies. A systematic review was conducted to understand the curative and side effects of vitamin D intake.
  
  
  RESULTS
  A total of 18 studies including eight cohort, five case-control, and five randomized studies met the inclusion criteria. The serum level of 25(OH)D in COPD patients was comparable with controls with a pooled SMD of 0.191 (95% CI: -0.126 to 0.508, P=0.237) based on pooled analyses of cohort studies. However, the serum level of 25(OH)D in COPD patients was lower with a pooled SMD of 0.961 (95% CI: 0.476-1.446, P<0.001) compared with controls based on pooled analyses of case-control studies. The deficiency rates of 25(OH)D were comparable between controls and COPD patients with a pooled RR of 0.955 (95% CI: 0.754-1.211, P=0.705) based on analyses of cohort studies, and the same results were observed based on pooled analyses of case-control studies. Interestingly, the deficiency rate of 25(OH)D was significantly lower in moderate or severe COPD patients with a pooled RR of 0.723 (95% CI: 0.632-0.828, P<0.001) compared with that in mild COPD patients. The same results were obtained from the pooled analysis between moderate and severe COPD patients. The four randomized studies showed that vitamin D intake provided benefit for COPD patients.
  
  
  CONCLUSIONS
  Low serum levels of 25(OH)D were not associated with COPD susceptibility, but the high deficiency rate of 25(OH)D was associated with COPD severity. Vitamin D supplementation may prevent COPD exacerbation.
authors.affiliation: The Fifth Internal Medicine Department, Guangzhou University of Chinese Medicine, Dongguan City, People's Republic of China.
authors.forename: Biyuan
authors.initials: B
authors.lastname: Zhu
authors.affiliation: Department of Laboratory Medicine, Guangzhou University of Chinese Medicine, Dongguan City, People's Republic of China.
authors.forename: Biqing
authors.initials: B
authors.lastname: Zhu
authors.affiliation: Department of Intensive Care Unit, Dongguan Hospital of Traditional Chinese Medicine, Guangzhou University of Chinese Medicine, Dongguan City, People's Republic of China.
authors.forename: Chaolie
authors.initials: C
authors.lastname: Xiao
authors.affiliation: The Fifth Internal Medicine Department, Guangzhou University of Chinese Medicine, Dongguan City, People's Republic of China.
authors.forename: Zhiwen
authors.initials: Z
authors.lastname: Zheng
mesh_terms: D019587:Dietary Supplements; D018450:Disease Progression; D006801:Humans; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications*; D012720:Severity of Illness Index; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000178:diet therapy*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25(OH)D; COPD; susceptibility