• Harri Hemilä and Elizabeth Chalker.
• Pol. Arch. Med. Wewn. 2025 Jan 13.

AbstractThis 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.

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