Vitamin C for preventing and treating the common cold

The standing Cochrane systematic review and meta-analysis of vitamin C for the common cold (29 trial comparisons, 11,306 participants for incidence). In the general community (10,708 participants), regular vitamin C supplementation did not reduce cold incidence (pooled risk ratio 0.97, 95% CI 0.94-1.00); in a subgroup of 598 marathon runners, skiers, and subarctic soldiers under brief extreme physical stress, incidence was roughly halved (RR 0.48-0.50 depending on the trial set). Regular supplementation modestly reduced cold duration (8% in adults, 14% in children); therapeutic vitamin C started after cold onset (7 comparisons, 3,249 episodes) showed no consistent benefit. DOI and PMID both resolved directly (PubMed record and Europe PMC record); title, authors (Hemilä, Chalker), journal, and abstract text match, including the pooled RR figures quoted in the case body.