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Vitamin C, Immunity, and Athletes

 

With early-year cold and flu season in full swing, athletes are all looking for ways to improve immunity and avoid illness.  The simple answer is to train appropriately, get rest, and eat a healthy diet.  However, since most people can’t cloister themselves away from humanity, it’s critical to find ways to bolster our defenses beyond common sense life habits.

Vitamin C has long been a recommended remedy and prevention for colds and other illnesses.   Despite the common belief in Vitamin C as an immunity booster, the overall evidence has been mixed on his effectiveness.  One recent study (Hemila 2013) reviewed twenty nine studies from 1966 to the present involving over 11,000 subjects.  Notably, reviewers found scant evidence showing that Vitamin C would improve immunity in general population.  Indeed, in twenty four trials meeting the standards of inclusion in the review, based on 10,708 subjects, there was only a 3% risk reduction in developing a cold. 

However, in five trials involving a total of 598 marathon runners, skiers and soldiers on subarctic exercises, there was 52% reduction in cold risk. (“vitamin C may be useful for people exposed to brief periods of severe physical exercise”).  Thus, for high workload athletes and those competing under extreme conditions, the use of Vitamin C for supplementation appears warranted.

Other findings in trials in which vitamin C was used for supplementation included:

  • In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%).
  • In children, 1 to 2 g/day vitamin C shortened colds by 18%.
  • The severity of colds was also reduced by regular vitamin C administration. 

In therapeutic trials, no consistent effect of vitamin C was seen on the duration or severity of colds, indicating that Vitamin C was not found effective for treatment.    Despite the lack of direct evidence on its effectiveness as treatment, authors concluded, “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.”

Conclusion

It is important to understand population and context, as its common for overly generalized claims to be made.  For general population, there’s no definitive evidence that vitamin C is effective for immunity.  That said, despite the classification of subjects as “general population”, it’s still possible that vitamin C may be useful for those undergoing high levels of general “life stress”.   High levels of “life stress” may make some general population lifestyles analogous to the competitive athlete population.  For athletes the evidence is much stronger, which is one reason vitamin C supplementation for those in high workload training programs remains well supported advice.    

Reference

Hemilä H, Chalker E.  Vitamin C for preventing and treating the common cold.  Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980. doi: 10.1002/14651858.CD000980.pub4.

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