Vitamin C for the common cold and pneumonia
MD Harri Hemilä, Elizabeth Chalker
Polish Archives of Internal Medicine, doi:10.20452/pamw.16926
This article provides an overview of vitamin C for preventing and treating respiratory infections. Studies in a wide variety of animals have shown vitamin C to be protective against infections. In controlled trials in the general human population, >1 g/day vitamin C did not prevent common colds. However, in 5 trials with participants undertaking heavy physical activity, vitamin C halved the incidence of colds. In 15 trials (N = 6244), regular supplementation of ≥1 g/day of vitamin C decreased the severity of colds by 15%. Results of therapeutic trials, in which vitamin C was initiated after common cold symptoms began, have been inconsistent. However, two therapeutic trials found that 6-8 g/day of vitamin C was twice as effective at reducing the duration of colds than 3-4 g/day. In three controlled trials, vitamin C prevented pneumonia, but the contexts were atypical: participants were schoolboys in a boarding school in the UK before WW-II, soldiers hospitalized for influenza A, and US marine recruits. It is unlikely that vitamin C would reduce the risk of pneumonia in the general population, however, four trials reported a treatment benefit for pneumonia patients, although the findings encourage further research rather than providing firm evidence of efficacy. Vitamin C has been tested for COVID-19 and sepsis with conflicting results. Given the evidence that vitamin C reduces the severity and duration of the common cold, and the safety and low cost, it is not unreasonable for individuals to test whether 6-8 g/day is beneficial at the individual level.
Conflict of interest None declared. Open access This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0), allowing anyone to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material, including commercial purposes, provided the original work is properly cited.  
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