Effects of Vitamin C Supplements on Clinical Outcomes and Hospitalization Duration for Patients with Coronavirus Disease 2019 (COVID-19): A Systematic Review and Meta-Analysis

Abstract Context Vitamin C has been used as an essential antioxidant to reduce the inflammatory response associated with pneumonia and acute respiratory distress syndrome in patients with the 2019 coronavirus disease (COVID-19), but its effect on clinical outcomes remains controversial and inconclusive. Objective The purpose of this study was to conduct a meta-analysis and systematic review to assess the effects of vitamin C supplementation on the severity of COVID-19 in hospitalized patients. Data Sources Web of Science, Embase, Cochrane Library, PubMed, CNKI, CSTJ, Wan fang, and CBM databases were searched for publications between January 2020 and December 2023 that met the inclusion criteria. Data Extraction The meta-analyses of outcomes in more than one study were performed using Review Manager software. Heterogeneity was evaluated using the I2 statistic. A randomized controlled trial, cohort studies, and retrospective studies in which vitamin C supplementation was supplemented as monotherapy or in combination, compared with placebo, no treatment, or other standard treatment without vitamin C were included. Data Analysis After screening, 22 studies, with a total of 3429 patients, were selected for assessment. Odds ratios (ORs) with 95% CIs were calculated using fixed- and random-effects models. The meta-analysis showed significant effects of vitamin C on alleviating clinical outcomes in patients with COVID-19 (OR = 0.76, 95% CI = 0.65–0.89, P = .0007) but no shortening of the length of hospitalization (MD = 1.16, 95% CI = −0.13–2.44, P = .08) compared with the control group. Notably, vitamin C supplements significantly reduced the mortality risk (OR = 0.64, 95% CI = 0.51–0.80, P = .0001) and the incidence of severity (OR = 0.59, 95% CI = 0.43–0.80, P = .0006) in COVID-19 patients. Conclusion The findings suggest that vitamin C supplements may have a beneficial effect on clinical outcomes, as well as reducing severity and mortality in COVID-19 patients, but more clinical randomized controlled trials are needed to evaluate the role of vitamin C in treating COVID-19. Systematic Review Registration PROSPERO registration no. CRD42023491517.