In addition , numerous trials have shown no difference regarding the most commonly studied endpoint : frequency of symptoms .
In 5 trials with participants under heavy acute physical stress ( 3 with marathon runners )  , vitamin C  reduced the incidence of colds by 52 % ( 95 % CI : 36 % to 65 % ) , but there is no evidence that vitamin C prevents colds in the general population .
Proponents of evidence -based medicine ( EBM ) emphasize that conclusions about medical interventions should be based on controlled trials with clinical ly relevant outcomes , so that the greatest weight should be given to the systematic review s of the trials .
So far , therapeutic supplementation has not been shown to be effective .
Preventing the common cold with a vitamin C supplement: A double-blind, placebo-controlled survey
One hundred sixty-eight volunteers were r and omized to receive a placebo or a vitamin C supplement , two tablets daily , over a 60-day period between November and February . They used a five-point scale to assess their health and recorded any common cold infections and symptoms in a daily diary . Compared with the placebo group , the active-treatment group had significantly fewer colds ( 37 vs 50 , P<.05 ) , fewer days challenged virally ( 85 vs 178 ) , and a significantly shorter duration of severe symptoms ( 1.8 vs 3.1 days , P<.03 ) . Consequently , volunteers in the active group were less likely to get a cold and recovered faster if infected . Few side effects occurred with the active treatment , and volunteers reported greatly increased satisfaction with the study supplement compared with any previous form of vitamin C. This well-tolerated vitamin C supplement may prevent the common cold and shorten the duration of symptoms . Volunteers were generally impressed by the protection afforded them during the winter months and the general acceptability of the study medication
In addition , numerous trials have shown no difference regarding the most commonly studied endpoint : frequency of symptoms .
In 5 trials with participants under heavy acute physical stress ( 3 with marathon runners )  , vitamin C  reduced the incidence of colds by 52 % ( 95 % CI : 36 % to 65 % ) , but there is no evidence that vitamin C prevents colds in the general population .
Proponents of evidence -based medicine ( EBM ) emphasize that conclusions about medical interventions should be based on controlled trials with clinical ly relevant outcomes , so that the greatest weight should be given to the systematic review s of the trials .
So far , therapeutic supplementation has not been shown to be effective .