Effects of Vitamin D on Respiratory Function and Immune Status for Patients with Chronic Obstructive Pulmonary Disease (COPD): A Systematic Review and Meta-Analysis

Abstract

Background: Many studies have demonstrated that vitamin D has clinical benefits when used to treat patients with chronic obstructive pulmonary disease (COPD). However, most of these studies have insufficient samples or inconsistent results. The aim of this meta-analysis was to evaluate the effects of vitamin D therapy in patients with COPD.

Methods: We performed a comprehensive retrieval in the following electronic databases: PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Data, and Chinese Scientific Journals Database (VIP). Two trained reviewers identified relevant studies, extracted data information, and then assessed the methodical quality by the Cochrane risk of bias assessment tool, independently. Then, the meta-analyses were conducted by RevMan 5.4, binary variables were represented by risks ratio (RR), and continuous variables were represented by mean difference (MD) or standardized mean difference (SMD) to assess the efficacy of vitamin D therapy in patients with COPD. Then, publication bias assessment was conducted by funnel plot analysis. Finally, the quality of evidence was assessed by the GRADE system.

Results: A total of 15 articles involving 1598 participants were included in this study. The overall results showed a statistical significance of vitamin D therapy in patients with COPD which can significantly improve forced expiratory volume in 1 second (FEV1) (MD: 5.69, 95% CI: 5.01-6.38,P < 0.00001,I2 = 51%) and FEV1/FVC (SMD:0.49, 95% CI: 0.39-0.60,P < 0.00001,I2 = 84%); and serum 25 (OH)D (SMD:1.21, 95% CI:1.07-1.34,P < 0.00001,I2 = 98%) also increase CD3+ Tcells (MD: 6.67, 95% CI: 5.34-8.00,P < 0.00001,I2 = 78%) and CD4+ T cells (MD: 6.00, 95% CI: 5.01-7.00,P < 0.00001,I2 = 65%); and T lymphocyte CD4+/CD8+ ratio (MD: 0.41, 95% CI: 0.20-0.61,P = 0.0001,I2 = 95%) obviously decrease CD8+ Tcells(SMD: -0.83, 95% CI: -1.05- -0.06,P < 0.00001,I2 = 82%), the times of acute exacerbation (RR: 0.40, 95% CI: 0.28-0.59,P < 0.00001,I2 = 0%), and COPD assessment test (CAT) score (MD: -3.77, 95% CI: -5.86 - -1.68,P = 0.0004,I2 = 79%).

Conclusions: Our analysis indicated that vitamin D used in patients with COPD could improve the lung function (FEV1 and FEV1/FVC), the serum 25(OH)D, CD3+ T cells, CD4 + T cells, and T lymphocyte CD4+/CD8+ ratio and reduce CD8+ T cells, acute exacerbation, and CAT scores.

Figure 1

Flow chart of the current study.

Figure 2

(a) Risk of bias graph. The image shows various possible biases in the meta-analysis. (b) Risk of summary. The image shows various possible risks in the meta-analysis.

Figure 3

Forest plot of the FEV1. Meta-analysis and heterogeneity test on the impact of vitamin D on FEV1 in patients with COPD.

Figure 4

Forest plot of the FEV1/FVC. The results show that in comparison to the control group, vitamin D supplementation can increase the FEV1/FVC of the experimental group and significantly facilitate the lung function of the patients.

Figure 5

Forest plot of the serum 25(OH)D. Meta-analysis unveiled that the study group was in comparison with the control after supplementation of vitamin D.

Figure 6

Forest plot of the CD3+ T cells. The results indicate that vitamin D supplementation can significantly enhance the percentage of CD3+ T cells.

Figure 7

Forest plot of the CD4+ T cells. The results indicated that the number of CD4+ T cells of the study group was higher than the control.

Figure 8

Forest plot of the CD8+ T cells. The results indicate that vitamin D can significantly decline CD8+ T cells in patients with COPD.

Figure 9

Forest plot of the CD4+/CD8+ T cells. Vitamin D could significantly improve the cell ratio of CD4+/CD8 + T in patients with COPD.

Figure 10

Forest plot of the acute exacerbations. The frequency of acute exacerbations in the vitamin D group decreased compared to the control.

Figure 11

Forest plot of the CAT scores. The results indicated that there were significant differences statistically in terms of CAT.

Figure 12

Funnel plot of publication bias. The results indicated there is no obvious publication bias.