Efficacy of Vitamin C Supplementation on Chronic Obstructive Pulmonary Disease (COPD): A Systematic Review and Meta-Analysis

BACKGROUND: In recent years, the pleiotropic roles of antioxidants have drawn extensive attention in various diseases. Vitamin C is a well-known antioxidant, and it has been used to treat patients with chronic obstructive pulmonary disease (COPD). This systematic review and meta-analysis aim to demonstrate the impact of vitamin C supplementation in patients with COPD. METHODS: We searched PubMed, Embase, Cochrane Library, Web of Science, Chinese National Knowledge Infrastructure (CNKI), SinoMed, Wanfang, and China Science and Technology Journal Database (cqvip.com) for eligible randomized controlled trials (RCTs) from their respective inception to May 18(th), 2021, by using the searching terms of COPD, vitamin C, and RCTs. A meta-analysis was performed to evaluate the effects of vitamin C on lung function, antioxidant levels, and nutritional conditions in COPD patients by using Review Manager (Version 5.4). RESULTS: Ten RCTs including 487 participants were eligible for our study. Meta-analysis results showed that vitamin C supplementation (≥400 mg/day) can significantly improve the forced expiratory volume in one second as a percentage (FEV1%) in COPD (SMD:1.08, 95% CI:0.03, 2.12, P=0.04). Moreover, vitamin C supplementation significantly improved the ratio of forced expiratory volume in 1 second and forced vital capacity (FEV1/FVC) (WMD:0.66, 95% CI: 0.26, 1.06, P=0.001), vitamin C level in serum (SMD:0.63, 95% CI: 0.02, 1.24, P=0.04) and glutathione (GSH) level in serum (SMD:2.47, 95% CI: 1.06, 3.89, P=0.0006). While no statistically significant difference was observed in body mass index (BMI), fat-free mass index (FFMI), vitamin E level and superoxide dismutase (SOD) level in serum. CONCLUSION: Vitamin C supplementation could increase the levels of antioxidation in serum (vitamin C and GSH) and improve lung function (FEV1% and FEV1/FVC), especially in patients treated with vitamin C supplementation greater than 400 mg/day. However, further prospective studies are needed to explore the role of vitamin C in improving nutritional status.