Vitamin C for preventing and treating colds and pneumonia
What it found
In people, taking vitamin C regularly did not prevent colds but made them shorter and milder.
Starting high doses right after symptoms began also helped in some trials.
What they found
Studies in people
Preventing colds in people
Across 24 trials with 10 708 people from the general public, taking over 1 g per day did not stop colds. But in 5 trials with 598 people doing heavy exercise like running or skiing, vitamin C halved the number of colds.
Shorter and milder colds
In 15 trials with 6244 people, taking 1 g or more daily cut how bad colds felt by 15%. In 17 trials with 7215 adults, it shortened colds by 7.7%, and in 10 trials with 1532 children, it shortened them by 18%.
Treating colds after they start
Results were mixed when people only took vitamin C after getting sick. However, 2 trials found that 6 to 8 g per day worked twice as well at shortening colds compared to 3 to 4 g per day.
Pneumonia prevention in people
Three trials prevented pneumonia, but only in unusual groups: boarding school boys before World War II, soldiers hospitalized for flu, and Marine recruits. The authors say this is unlikely to apply to the general public.
Animal and lab studies
Protection in animal studies
Out of 148 animal studies, 86 showed vitamin C protected against infections. Benefits were seen in guinea pigs, rats, mice, birds, and fish against viruses, bacteria, and other germs.
Other findings
Dose comparisons are tricky
Unlike drug trials, control groups still get some vitamin C from food. This makes it hard to compare studies because the starting amounts vary widely between different trials.
What the authors conclude
- They say there is no reason for the general public to take vitamin C every day just to avoid catching a cold.
- They suggest that people who get frequent colds could try taking it during winter to see if it helps them personally.
- They advise that anyone with a cold could reasonably try 6 to 8 g per day split into smaller doses, starting right after symptoms appear.
How it was done
Many infections lower vitamin C levels in the body, and white blood cells hold about 100 times more of it than blood plasma. The authors wanted to gather the clinical evidence on whether extra vitamin C helps with breathing infections.
The authors gathered and examined controlled trials in people and animals looking at vitamin C for colds, pneumonia, sepsis, and COVID-19. They looked at studies involving thousands of participants across many decades, including a trial of 29 133 men followed for 6 years and another pooling 15 trials with 6244 people.
What it can’t tell you
- These findings come from many different trials, so results may not apply equally to everyone.
- Some benefits were only seen in specific groups like soldiers or people doing heavy exercise.
- Observational studies following people over time can show links but cannot prove that vitamin C caused the changes.
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 · animals · lab
- Summarised from
- Full text
- Cite
- Hemilä H, Chalker E (2025). Vitamin C for the common cold and pneumonia. Polish archives of internal medicine. doi:10.20452/pamw.16926Free full textPubMed 39803741DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error