Daily supplements of vitamin C may reduce the risk of developing common cold for marathon runners by 50%, but there is little evidence that it helps the rest of us, says a new Cochrane review.
Data from five trials with 598 marathon runners, skiers and soldiers on subarctic exercises indicated that the risk of common cold was reduced by 52% for vitamin C supplements of 0.2 g per day or more, according to findings published in The Cochrane Library.
However, data from 24 trials involving 10,708 participants from the general community revealed no significant changes to the risk of common cold.
Select analysis further revealed that vitamin C supplements did reduce the duration of common colds in adult and children by 8% and 14%, respectively.
In addition, a dose of 1 to 2 grams per day reduced the duration by 18% for children.
“The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise,” wrote Harri Hemila from the University of Helsinki in Finland, and Elizabeth Chalker from Curtin, ACT in Australia.
“Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out.
“Nevertheless, 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.”
The common cold is one of the most widespread illnesses in the world. It is estimated that adults suffer from between two and four episodes annually, whilst children in school may have as many as 12 episodes per year.
A recent Cochrane review estimated that the total economic impact of cold-related work loss exceeds $20 billion per year. As a result, Americans spend around $2.9 billion on over-the-counter drugs (and another $400 million on prescription medicines) for symptomatic relief of cold.
Benefits for athletes?
Commenting on the potential effects in athletes, Hemila and Chalker noted: “The doses of vitamin C were not particularly high, being between 0.25 and 1.0 g/day. Thus, the benefit in this subgroup cannot be explained by high vitamin C doses. Similar and higher doses in the general community have not affected the incidence of colds.”
The authors explained that in the general population that respiratory symptoms are usually linked to a virus, but for athletes may also be related to injury to the airways from heavy breathing that produce exercise-induced bronchoconstriction (EIB) symptoms.
“Thus the common cold studies of physically stressed people might have been measuring, at least in part, the effects of vitamin C on EIB instead of viral infections. Nevertheless, although the aetiology of symptoms is not clear in the physically stressed subgroup, the beneficial effect of vitamin C on acute respiratory symptoms in this subgroup is firm.”
Source: The Cochrane Library
Published online, January 31, 2013. doi: 10.1002/14651858.CD000980.pub4
“Vitamin C for preventing and treating the common cold”
Authors: H. Hemila, E. Chalker