Effect of Vitamin C Supplements on Respiratory Tract Infections: A Systematic Review and Meta-Analysis

Abstract

Background: Respiratory tract infections are a primary cause of illness and mortality over the world. We aimed to gather evidence on the effectiveness of vitamin C supplementation in preventing and treating the respiratory tract infections among adults and children. Methods: To investigate the effectiveness of vitamin C supplementation on respiratory tract infections, we conducted a systematic review and meta-analysis of studies. We used the Cochrane, PubMed, and MEDLINE Ovid database to conduct our search. Data was extracted independently by three review authors. The inclusion criteria were placebo-controlled trials that examined the effectiveness of vitamin C supplementation in preventing and treating the respiratory illness. Random effects meta-analyses were performed to measure the pooled effects of vitamin C supplementation on the incidence, severity, and duration of respiratory illness. Findings: We found ten studies that met our inclusion criteria out of a total of 2758.The pooled risk ratio (RR) of developing respiratory illness whilst taking vitamin C regularly across the study period was 0⸳94 (with a 95% confidence interval of 0⸳87 to 1⸳01) which found that supplementing with vitamin C lowers the occurrence of illness. This effect, however, was statistically insignificant (P= 0⸳09). This study showed that vitamin C supplementation had no consistent effect on the severity of respiratory illness (SMD 0⸳14, 95% CI -0⸳02 to 0⸳30: I2 = 22%, P=0⸳09). However, our study revealed that vitamin-C group had a considerably shorter duration of respiratory infection (SMD -0⸳36, 95% CI -0⸳62 to -0⸳09, P = 0⸳01). Interpretation: The benefits of normal vitamin C supplementation for reducing the duration of respiratory tract illness were supported by our meta-analysis findings. Since few trials have examined the effects of therapeutic supplementation, further therapeutic trials are required to examine the role of vitamin C in the treatment of respiratory infection especially COVID-19 infection. Funding Information: None.Declaration of Interests: We declare no competing interests.