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 .
Vitamin C as a preventive medicine against common colds in children.
During 7 weeks in the spring of 1973 a double-blind pilot study on 172 children in the age group 8 - 9 was carried out to test the possible effect of 1000 mg vitamin C daily as a prophylactic agent against common colds . During the autumn of 1973 , a main study was carried out on 642 children of the same age . The investigations had the same pattern and lasted for 3 months . Both studies have been processed on the same principles . The results were somewhat divergent but , like previously published studies on children , seemed to indicate that the duration and severity of the cold were reduced while , on the other h and , the incidence remained unaltered or indeed increased . The total number of days of upper respiratory tract infection was smaller for the vitamin C group only in the pilot study ( not in the main study ) . No proven biochemical effects were obtained . Preventive treatment of healthy children with vitamin C in large doses this had no definitely proved effect against colds
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 .