Does Vitamin C Help Prevent Flu
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Evidence Summary
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Vitamin C does not prevent the common cold but may reduce its duration and severity
Hemila H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013:1: CD000980.
Review question
In adults and children, does vitamin C reduce the incidence, duration, or severity of the common cold when used either as a continuous regular supplement every day or as treatment at the start of cold symptoms?
Background
Respiratory viruses (of some 200 types) are the usual cause of the common cold. Antibiotics are not useful for an acute occurrence of the common cold because they kill bacteria and not viruses. So, other treatment options for colds are of major public health interest. Since the early 1940s, many research studies have examined the possible effects of vitamin C on the common cold.
Incidence of the common cold refers to the number of people who catch it. Duration refers to the number of days of illness of cold occurrences. Severity refers to the days confined indoors, off work, off school, and how bad it is.
How the review was done
This summary is based on a review of 63 randomized controlled trials with 11,306 adults and children. 60 trials were based in the community and 3 in the lab. Most of the trials (43) focused on regular supplements of vitamin C to prevent a person from getting a cold. 10 trials focused on the use of vitamin C as a treatment once the natural cold symptoms had started.
What the researchers found
When vitamin C was used as a regular supplement to prevent a person from getting a cold (with doses of at least 0.2 grams/day), the duration of colds was reduced by 8% in adults and 14% in children. In children, higher doses (1 to 2 grams/day) shortened colds by 18%. The severity of colds was also reduced by regular vitamin C supplements. Vitamin C did not reduce the number of people who caught colds. While these results were consistent across studies, their effect was small.
The use of vitamin C as treatment (that is, once the cold symptoms started) did not reduce the duration and severity of the cold when compared to people who did not receive it.
Conclusion
Vitamin C as a supplement before a cold starts does not prevent it but may reduce its duration and severity.
Effects of vitamin C on the common cold in adults
| Use of vitamin C | Prevents catching a cold | Reduces cold duration once caught | Reduces cold severity once caught |
| As regular supplements before a cold starts | no | a little | a little |
| As treatment once a cold has started | – | no | no |
Effects of vitamin C on the common cold in children
| Use of vitamin C | Prevents catching a cold | Reduces cold duration once caught | Reduces cold severity once caught |
| As regular supplements before a cold starts | no | a little | a little |
| As treatment once a cold has started | – | not studied | not studied |
Glossary
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
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DISCLAIMER These summaries are provided for informational purposes only. They are not a substitute for advice from your own health care professional. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the McMaster Optimal Aging Portal (info@mcmasteroptimalaging.org).
Does Vitamin C Help Prevent Flu
Source: https://www.mcmasteroptimalaging.org/full-article/es/vitamin-prevent-common-cold-reduce-duration-severity-2
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