Vitamin C appears to be especially beneficial for individuals under intense physical stress. In five studies of people with intense short term physical stress, the incidence of the common cold was cut in half with the use of vitamin C.
Three of the studies observed marathon runners, one researched Swiss school children at a skiing camp and another observed Canadian soldiers for the duration of a winter exercise.
In addition, in a recent study conducted with teenage competitive swimmers, the duration of colds in males was cut in half with vitamin C, but the vitamin didn’t have any effect on females.
Daily doses of vitamin C of 1 gram or more have reduced the typical duration of colds in adults by 8 percent and in children by 18 percent.
Even though these results clearly demonstrate that vitamin C does have a biological influence on colds, consuming vitamin C each day to shorten occasional colds doesn’t seem to realistic. Generally, adults only have a number of common cold episodes annually and children get as few as 6 colds each year.
Few therapeutic studies, which means studies in which vitamin C was administered only once the 1st symptoms of a cold developed, have been conducted and their outcomes are not consistent. Even so, considering the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation research, and the safety and affordability of vitamin C, the study authors consider that it could be beneficial for individual common cold sufferers to try whether therapeutic vitamin C is effective for them.