Vitamin C for preventing and treating the common cold.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized placebo-controlled trials.
PubMed 17636648 · doi:10.1002/14651858.CD000980.pub3
What was done
Systematic review and meta-analysis searching CENTRAL, MEDLINE, and EMBASE through December 2006 for placebo-controlled trials evaluating oral vitamin C at doses of 0.2 g/day or more. The review examined continuous daily prophylaxis as well as therapeutic administration initiated after symptom onset to assess cold incidence, duration (mean days of illness), and symptom severity.
What was found
Prophylactic vitamin C did not reduce cold incidence in the general community across 30 trial comparisons with 11,350 participants (pooled RR 0.96, 95% CI 0.92 to 1.00). In a subgroup of 6 trials involving 642 marathon runners, skiers, and soldiers on sub-arctic exercises, prophylaxis halved cold risk (pooled RR 0.50, 95% CI 0.38 to 0.66). Continuous prophylaxis (30 comparisons, 9,676 episodes) reduced cold duration by 8% (95% CI 3% to 13%) in adults and 13.6% (95% CI 5% to 22%) in children. Post-onset therapeutic vitamin C showed no significant difference from placebo for cold duration (7 comparisons, 3,294 episodes) or cold severity (4 comparisons, 2,753 episodes).
Why it matters
Routine high-dose vitamin C supplementation is not justified for community cold prevention, though it offers modest benefit for illness duration and prevents colds in individuals exposed to extreme physical or environmental stress.
Limits
The therapeutic evidence base (treatment started post-onset) is substantially smaller than the prophylactic evidence base. Exact doses varied across included studies above the 0.2 g threshold, and baseline dietary vitamin C intake and specific viral causes were not characterized in the abstract.
Cited by
- supports Six trials in over 600 marathon runners, skiers, and soldiers showed a 50% reduction in cold incidence with supplemental vitamin C.
- supports A comparison of 12 clinical trials found that vitamin C supplementation reduced cold duration by 13.5% in children and 8% in adults.