• Harri Hemilä and Elizabeth Chalker.
• Pol. Arch. Med. Wewn. 2025 Jan 30; 135 (1).

AbstractThis paper provides an overview of the efficacy 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, vitamin C at a dose greater than 1 g/day 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 or more of vitamin C per day decreased the severity of colds by 15%. Results of therapeutic trials in which vitamin C was initiated after the onset of common cold symptoms have been inconsistent. However, 2 therapeutic trials found that 6-8 g/day of vitamin C was twice as effective at reducing the duration of colds as 3-4 g/day. In 3 controlled trials, vitamin C was shown to prevent pneumonia, but the contexts were atypical: the participants were schoolboys attending a boarding school in the United Kingdom before World War II, soldiers hospitalized for influenza A, and United States Marine recruits. It is unlikely that vitamin C would reduce the risk of pneumonia in the general population; however, 4 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 efficacy in COVID‑19 and sepsis with conflicting results. Given the evidence that vitamin C reduces the severity and duration of the common cold, paired with its good safety profile and low cost, it is not unreasonable for patients to test whether therapeutic vitamin C supplementation at a dose of 6-8 g/day is beneficial at the individual level.

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