Vitamin C for the common cold and pneumonia.

2025-01-13
Polish archives of internal medicine 135(1)
- Harri Hemilä
- Elizabeth Chalker

PubMed: 39803741
DOI: 10.20452/pamw.16926

Study Design

Type: Review
Sample size: n = 6,244
Population: participants from 15 trials (n = 6244) and various specific groups (e.g., schoolboys, soldiers, Marine recruits)
Methods: review of controlled trials and other studies on vitamin C

This 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.

Research Insights

Vitamin C→Improved COVID-19 Outcome
Vitamin C has been tested for efficacy in COVID‑19 and sepsis with conflicting results.
Effect
Neutral
Effect size
Small
Dose
6-8 g/day
Vitamin C→Improved Pneumonia Outcome
4 trials reported a treatment benefit for pneumonia patients, although the findings encourage further research rather than providing firm evidence of efficacy.
Effect
Beneficial
Effect size
Small
Dose
6-8 g/day
Vitamin C→Improved Sepsis Outcome
Vitamin C has been tested for efficacy in COVID‑19 and sepsis with conflicting results.
Effect
Neutral
Effect size
Small
Dose
6-8 g/day
Vitamin C→Prevented Common Cold
In controlled trials in the general human population, vitamin C at a dose greater than 1 g/day did not prevent common colds.
Effect
Neutral
Effect size
Small
Dose
greater than 1 g/day
Vitamin C→Prevented Pneumonia
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.
Effect
Beneficial
Effect size
Moderate
Dose
6-8 g/day
Vitamin C→Reduced Common Cold Duration
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.
Effect
Beneficial
Effect size
Moderate
Dose
6-8 g/day
Vitamin C→Reduced Incidence of Common Cold
in 5 trials with participants undertaking heavy physical activity, vitamin C halved the incidence of colds.
Effect
Beneficial
Effect size
Large
Dose
1 g or more per day
Vitamin C→Reduced Pneumonia Risk
It is unlikely that vitamin C would reduce the risk of pneumonia in the general population;
Effect
Neutral
Effect size
Small
Dose
6-8 g/day
Vitamin C→Reduced Severity of Common Cold Symptoms
In 15 trials (n = 6244), regular supplementation of 1 g or more of vitamin C per day decreased the severity of colds by 15%.
Effect
Beneficial
Effect size
Moderate
Dose
1 g or more per day

Adverse Events Reported

Vitamin C→Overall tolerability
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.
Finding
Reported