Vitamin C and the severity of common colds
What it found
In people, taking at least 1 g of vitamin C a day reduced how severe colds were by about 15% on average.
In a smaller set of trials, it cut the length of severe symptoms by about 26% but made no difference to mild symptoms.
What they found
Studies in people
Overall severity reduced
Across all 15 comparisons, vitamin C lowered the severity of common colds by 15% on average compared with placebo. This was a highly significant result.
Days off and indoors
In three trials with 2736 people, vitamin C shortened days absent from school or confined to the house by 15% on average. The larger Swedish trial in schoolchildren found an 18% reduction in school absence.
Severe symptoms shortened
Two short trials in people under physical stress in cold climates found about a 60% reduction in the duration of severe symptoms such as headache, chills and fever. The confidence intervals were wide.
Mild versus severe
In five trials with 2753 cold episodes, vitamin C cut the duration of severe symptoms by 26% but had no significant effect on mild symptoms. The difference between the two was statistically significant.
Severity scale scores
Seven comparisons using severity scales found vitamin C lowered severity by 13% on average. One trial in US marine recruits found a 10% reduction.
Who benefited more
In one large Canadian trial, vitamin C reduced days confined to the house by 1.12 days in people who had contact with young children, but by only 0.26 days in those who did not. The benefit was also greater for people who usually had two or more colds per winter.
What the authors conclude
“Vitamin C substantially decreased the severity of colds without influencing their overall duration.”
Also in their conclusions
- They found a significant difference in the effect of vitamin C on mild versus severe outcomes of the common cold.
- They say vitamin C substantially decreased the severity of colds without influencing their overall duration.
- They suggest the 15 to 26% decrease in cold severity may justify regular vitamin C for some people, such as those who have frequent contact with young children, and call for more research on therapeutic vitamin C started right after symptoms begin.
How it was done
Antibiotics do not work against colds, which are almost always caused by viruses, and about half of US cold patients still get them. The authors wanted to compare how vitamin C affects severe versus mild cold symptoms, since severe symptoms are what keep people off work and school.
They pooled 10 placebo-controlled trials with 15 comparisons, all in people in good health at the start, taking at least 1 g of vitamin C a day by mouth. Trials ran from about a week to 5 months and reported both overall cold duration and a measure of severity, such as days off school, days confined to the house, or symptom scores.
What it can’t tell you
- The trials used different definitions of a cold and different severity measures, so the 15% and 26% figures are approximations rather than universal estimates.
- In several trials the placebo group was already getting extra vitamin C from diet or supplements, which would make the benefit of vitamin C look smaller than it really is.
- The analysis treated severe and mild symptoms as if they were independent, but they come from the same people, so the statistical comparison between them should be viewed with some caution.
Who paid
- Conflicts
- The authors declare no competing interests.
- Authors work at
- University of Helsinki, Finland; Australian National University, Australia
The paper
- Title
- Vitamin C reduces the severity of common colds: a meta-analysis
- Type
- Meta-analysis
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Hemilä H, Chalker E (2023). Vitamin C reduces the severity of common colds: a meta-analysis. BMC public health. doi:10.1186/s12889-023-17229-8Free full textPubMed 38082300DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error