Vitamin C (ascorbate) has been widely used to support or treat the common cold, primarily based on both traditional use and scientific investigation. The scientific evidence for its effectiveness is modest. Multiple randomized controlled trials and systematic reviews (notably, the Cochrane review by Hemilä and Chalker, 2013) have assessed vitamin C’s role in preventing and treating colds. For the general population, routine high-dose supplementation does not significantly reduce the incidence of colds. However, regular supplementation (≥200 mg/day) has been shown to produce a small but consistent reduction in the duration and severity of cold symptoms (typically about 8% in adults and 14% in children).

The proposed mechanism is not directly antiviral but rather related to vitamin C’s role in immune function, as an antioxidant and in supporting various cellular functions of the immune system. Some evidence suggests that individuals undergoing extreme physical stress (e.g., marathon runners) may derive greater benefit in terms of cold prevention.

In summary, while there is scientific evidence supporting a minor benefit of vitamin C in reducing the duration and severity of colds, its use as a primary antiviral treatment is not strongly validated. The evidence does not support large effects or routine use for prevention in the general population, but regular supplementation may offer modest benefits for some individuals.