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Is it worth taking vitamin C to prevent and treat the common cold?

Summary of a new Cochrane review that could apply to your next consultation

Summary of a new Cochrane review that could apply to your next consultation

Do oral doses of 0.2g or more daily of vitamin C reduce the incidence, duration or severity of the common cold when used either as continuous prophylaxis or after the onset of symptoms?

Vitamin C (ascorbic acid) and its role in the prevention and treatment of the common cold has been a subject of controversy for 60 years, but it is widely sold and used as both a preventive and therapeutic agent.

Methods

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2006); MEDLINE (1966 to December 2006); and EMBASE (1990 to December 2006). Papers were excluded if a dose less than 0.2g per day of vitamin C was used, or if there was no placebo comparison.

Two review authors independently extracted data and assessed trial quality. ‘Incidence' was assessed as the proportion of participants experiencing one or more colds during the study period. ‘Duration' was the mean days of illness of cold episodes.

Main results

Some 30 trial comparisons involving 11,350 participants contributed to the meta-analysis on the relative risk (RR) of developing a cold while taking prophylactic vitamin C. The pooled RR was 0.96 (95% confidence intervals (CI) 0.92 to 1.00). A subgroup of six trials involving a total of 642 marathon runners, skiers, and soldiers on sub-arctic exercises reported a pooled RR of 0.50 (95% CI 0.38 to 0.66).

Some 30 comparisons involving 9,676 respiratory episodes contributed to a meta-analysis on cold duration during prophylaxis. A consistent benefit was observed, representing a reduction in cold duration of 8% (95% CI 3-13%) for adults and 13.6% (95% CI 5-22%) for children.

Seven trial comparisons involving 3,294 respiratory episodes contributed to the meta-analysis of duration during vitamin C therapy initiated after the onset of symptoms. No significant benefits were seen.

Four trial comparisons involving 2,753 respiratory episodes contributed to the meta-analysis of cold severity during therapy and no significant benefits were seen.

Authors' conclusions

The failure of vitamin C to reduce the incidence of colds indicates that routine mega-dose prophylaxis is not rationally justified for community use. But evidence suggests it could be justified in people exposed to brief periods of severe physical exercise or cold environments.

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