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 23440782 · doi:10.1002/14651858.CD000980.pub4
What was done
Systematic review and meta-analysis of placebo-controlled trials testing vitamin C (at least 0.2 g/day) administered regularly or therapeutically at cold onset. Searches covered CENTRAL, MEDLINE, EMBASE, CINAHL, LILACS, Web of Science, and clinical trial registries through November 2012. Primary outcomes were cold incidence during regular supplementation, duration in days, and cold severity.
What was found
Regular supplementation in general community trials did not reduce cold incidence (29 comparisons, n=10,708; RR 0.97, 95% CI 0.94 to 1.00). In 5 trials of marathon runners, skiers, and subarctic-deployed soldiers (n=598), regular supplementation halved cold incidence (RR 0.48, 95% CI 0.35 to 0.64). Across 31 comparisons (9,745 episodes), regular vitamin C reduced cold duration by 8% (95% CI 3% to 12%) in adults and by 14% (95% CI 7% to 21%) in children (18% reduction with 1 to 2 g/day in children), with reduced symptom severity. Therapeutic trials initiated after symptom onset (7 comparisons, 3,249 episodes) showed no consistent effect on duration or severity.
Why it matters
Routine vitamin C supplementation is not justified for general cold prevention, though it modestly shortens episode duration if taken continuously and substantially protects individuals undergoing short-term extreme physical exertion.
Limits
Data on therapeutic use started after symptom onset are limited to few trials with inconsistent results. Subgroup analyses by dose, specific viral etiology, and baseline dietary vitamin C intake were not fully resolved in the abstract.
Cited by
- supports Consuming vitamin C in doses above 250 mg per day helps prevent upper respiratory tract infections, particularly in high-volume endurance athletes.