Vitamin C for colds and pneumonia
What it found
In people, vitamin C did not prevent colds at doses over 1 g/day, but it cut cold severity by 15% and halved colds in people doing heavy physical activity.
It also showed some benefit for pneumonia in certain groups.
What they found
Studies in people
Colds in general population
In controlled trials, vitamin C at a dose greater than 1 g/day did not prevent common colds in the general human population.
Colds in heavy activity
In 5 trials with participants doing heavy physical activity, vitamin C halved the incidence of colds.
Cold severity
In 15 trials with 6244 people, regular supplementation of 1 g or more of vitamin C per day decreased the severity of colds by 15%.
Cold duration
Two 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.
Pneumonia prevention
In 3 controlled trials, vitamin C prevented pneumonia, but the contexts were atypical: schoolboys in a UK boarding school before World War II, soldiers hospitalized for influenza A, and US Marine recruits.
Pneumonia treatment
Four trials reported a treatment benefit for pneumonia patients, but the findings encourage further research rather than providing firm evidence.
What the authors conclude
“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.”
Also in their conclusions
- They say it is unlikely that vitamin C would reduce the risk of pneumonia in the general population.
- They note that 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.
How it was done
The authors wanted to review how well vitamin C works for preventing and treating respiratory infections like the common cold and pneumonia.
They looked at controlled trials in people, including 15 trials with 6244 people taking 1 g or more of vitamin C daily, and other trials in animals and specific groups like soldiers and schoolboys.
What it can’t tell you
- We summarised it from the abstract only.
- The pneumonia prevention trials were in atypical groups like schoolboys and soldiers, so the results may not apply to the general population.
- The therapeutic trials for colds had inconsistent results, so it is not clear when vitamin C after symptoms start will help.
- The findings for pneumonia treatment encourage further research rather than providing firm evidence of efficacy.
The paper
- Title
- Vitamin C for the common cold and pneumonia
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Hemilä H, Chalker E (2025). Vitamin C for the common cold and pneumonia. Polish archives of internal medicine. doi:10.20452/pamw.16926PubMed 39803741DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error