The role of vitamin C in preventing and treating colds has been a cause of disagreement for 70 years already.
Does vitamin C reduce the risk of catching a cold, the duration of a cold or severity of symptoms? When is it most effective – when used continuously or upon appearance of the first symptoms? In order to find the answers to these questions, a summary of 93 studies involving a total of 11 306 subjects was made1. The range of subjects included people under extreme conditions – marathon runners, skiers and soldiers (n=598). The data analysis also took into account studies where the administered dose of vitamin C was equal to or greater than 200 mg per day. In the groups taking vitamin C regularly, the number of sick days was on average 8% lower for adults (3-12%) and 14% for children (7-21%). Regular use of vitamin C also reduces the severity of cold symptoms. Furthermore, supplementing vitamin C is recommended for people temporarily subject to intense physical activity. In turn, taking vitamin C “at the last minute”, when the first symptoms of a cold have already appeared, has no effect whatsoever. Taking vitamin C after the appearance of cold symptoms does not reduce the duration, nor the severity of the cold. However, researchers conclude that given the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, and the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them.
1 Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold.Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980.