Evidence Level
Strong
Vitamin C has a robust evidence base spanning decades of research. The landmark 2013 Cochrane review by Hemilä and Chalker analyzed 29 trials (n=11,306) and found that regular vitamin C supplementation (≥200 mg/day) reduced cold duration by 8% in adults but did not reduce cold incidence in the general population. However, five trials in participants under heavy physical stress (marathon runners, soldiers, skiers) showed a 52% reduction in cold incidence. Carr and Maggini (2017) reviewed vitamin C's role in immune function, demonstrating it supports both innate and adaptive immunity through multiple mechanisms including neutrophil function, lymphocyte proliferation, and antibody production.