Vitamin D deficiency is associated with the severity of COPD: a systematic review and meta-analysis

Abstract

Purpose: 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.

Conclusion: 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.

Keywords: 25(OH)D; COPD; susceptibility.

Figure 1

A flowchart of identified studies. Abbreviation: 25(OH)D, 25-hydroxyvitamin D.

Figure 2

Forest plots of the serum level of 25(OH)D in the controls and COPD patients. Notes: Weights are from random-effects analysis. *Low-risk COPD: FEV₁%pred ≥50% and less than two treated exacerbation per year. ^#High-risk COPD: FEV₁%pred <50%, or two or more treated exacerbations per year, or one or more hospitalizations for COPD exacerbations per year. Abbreviations: CI, confidence interval; FEV₁%pred, forced expiratory volume in 1 second (FEV₁)/forced vital capacity (FVC) predicted; SMD, standard mean difference.

Figure 3

Forest plots of the deficiency rate of serum 25(OH)D. Notes: (A) Pooled analysis of the deficiency rates of 25(OH)D between controls and COPD patients in the cohort studies. Weights are from random-effects analysis. (B) Pooled analysis of the deficiency rates of 25(OH)D between the controls and COPD patients in the case-control studies. (C) Pooled analysis of the deficiency rates of 25(OH)D between the mild and moderate/severe COPD patients. (D) Pooled analysis of the deficiency rates of 25(OH)D between moderate and severe COPD patients. Weights are from random-effects analysis. Abbreviations: 25(OH)D, 25-hydroxyvitamin D; CI, confidence interval; RR, relative ratio.