section name header

Evidence summaries

Vitamin C for Preventing and Treating the Common Cold

Vitamin C supplementation appears not to reduce the incidence of colds in the general population, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise. There is a consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, but this finding is not replicated in therapeutic trials. Level of evidence: "B"

Comment: The quality of evidence is downgraded by inconsistency (unexplained variability in results).

A Cochrane review [Abstract] 1 included 63 trials, reported in 44 publications. All trials tested 0.2 g/day or more of vitamin C. The trials fall to following categories

  1. Community regular supplementation trial arms (43) which evaluated the effects of regular daily supplementation with vitamin C (i.e. vitamin C each day over the study irrespective of the presence of colds) on reducing the incidence or duration or severity of naturally occurring colds.
  2. Community therapeutic trial arms (10) that evaluated the therapeutic effects of high-dosage vitamin C after natural common cold symptoms had commenced.
  3. Community trials (7), which did not report data suitable for meta-analysis.
  4. Laboratory trials (3) in which volunteers were intentionally exposed to known viruses after vitamin C or placebo administration.

The primary end point was the risk ratio (RR) of developing at least one cold whilst taking vitamin C regularly over the study period, ranging from 2 weeks to 5 years. In the general community trials, where people had no heavy short-term physical stress, the pooled RR was 0.97 (95% CI 0.94 to 1.00; 24 trials, n=10 708). Trials involving marathon runners, skiers and soldiers on subarctic exercises yielded a pooled RR of 0.48 (95% CI 0.35 to 0.64; 5 trials, n=598).

Thirty-one comparisons examined the effect of regular vitamin C on common cold duration (9 745 episodes). In adults the duration of colds was reduced by 8% (4% to 12%) and in children by 14% (7% to 21%). In children, 1 to 2 g/day vitamin C shortened colds by 18%. The severity of colds was also reduced by regular vitamin C administration. Seven comparisons examined the effect of therapeutic vitamin C (3 249 episodes). No consistent effect of vitamin C was seen on the duration or severity of colds in the therapeutic trials.

Clinical comment: Routine vitamin C supplementation is not justified in the prevention of common cold, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise.

    References

    • Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2013;(1):CD000980. [PubMed]

Primary/Secondary Keywords