Vitamin C for preventing and treating the common cold.

Included 55 placebo-controlled trials from 1940 to 2004, focusing on various populations including marathon runners, skiers, and soldiers.

Investigated the effect of vitamin C (200 mg or more daily) on the common cold's incidence, duration, and severity.

Vitamin C did not affect the incidence of colds in the general population but showed a 50% reduction in those exposed to significant stress. There was a minor reduction in the duration of colds for children and adults during prophylaxis, while therapeutic use at the onset showed mixed results needing further research.

Lack of data on the therapeutic use of vitamin C in children and variable quality of included trials.