The Pharmaceutical Journal
Vol 275 No 7356 p7
2 July 2005

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Review throws doubt over use of vitamin C for prevention of colds

Researchers looked at data from 29 studies conducted over the past 65 years. They found that the incidence of colds was not altered in the 23 studies that examined the impact of prophylactic vitamin C (up to 2g daily) in the general population.

“The lack of effect of prophylactic vitamin C supplementation on the incidence of common cold in normal populations throws doubt on the utility of this wide practice,” the researchers write.

There were some benefits to the use of vitamin C, however. A subgroup of six studies of marathon runners, skiers and soldiers exposed to physical exertion or extreme cold showed a reduction, on average, of 50 per cent in the incidence of colds.
Furthermore, adults who developed a cold and who were taking vitamin C experienced, on average, an 8 per cent reduction in the number of days with cold symptoms compared with those who were given placebo. For children the effect was more marked, with a 14 per cent reduction in days with symptoms.

As a treatment, vitamin C was not effective. The researchers found seven trials designed to test whether the vitamin could shorten the duration of a cold if it were taken when symptoms started. Only one trial, in which participants took either a high dose of vitamin C (8g) or placebo, showed a shortening of cold duration for the vitamin group.

Details of the review are published online in PLoS Medicine (www.plosmedicine.org).