Vitamin C Can't Cure Common Cold
Tiny Cold-Shortening Effect Not Worth Yearlong Dosing
WebMD News Archive
July 17, 2007 -- Vitamin C can't cure common colds -- and, for most people,
it can't do much to prevent them.
That's the word from a brand new review of some 60 years of clinical
research by Robert M. Douglas, MD, emeritus professor at Australian National
University, Canberra, and colleagues.
Vitamin C affects resistance to viruses in lab animals. That's led to
decades of speculation that vitamin C supplements could be used to treat or to
prevent the common cold.
It's also led to a large number of clinical trials, which tested a wide
range of vitamin C doses in a wide range of people. In a prestigious Cochrane
Review, Douglas and colleagues used widely accepted techniques for analyzing
all these studies.
- When taken after a cold starts, vitamin C supplements do not make a cold
shorter or less severe.
- When taken as a daily preventive medicine, vitamin C very slightly shortens
cold duration -- by 8% in adults and by 13.6% in children.
- When given as a preventive medicine to highly fit people in conditions of
extreme cold -- data based mostly on marathon runners -- vitamin C cuts the
risk of getting a cold in half.
The average adult who suffers with colds for 12 days a year would still
suffer for 11 days a year if that person took a high dose of vitamin C every
"It would not seem reasonable to ingest vitamin C regularly in the
mega-dose range throughout the year if the only anticipated benefit is to
rather slightly shorten the duration of colds, which occur for adults only two
or three times a year," Douglas and colleagues suggest.
For the average child who suffers about 28 days of cold illness a year,
taking daily high-dose vitamin C would still mean 24 days of cold illness.
"Such a benefit is not trivial but is it worth the cost of long-term
prophylaxis?" Douglas and colleagues ask.
The only strong effect of vitamin C was in preventing colds among people
engaged in extreme physical exercise in extremely cold conditions.
"Caution should be exercised in generalizing this finding that is mainly
based on marathon runners," Douglas and colleagues caution.
A better way to prevent the common cold: regular and careful hand washing, especially during cold
Douglas and colleagues report their findings in The Cochrane