TOKYO, Japan--According to a study published online in the Aug. 24 issue of the European Journal of Clinical Nutrition (DOI:10.1038/sj.ejcn.1602261), vitamin C supplementation appears to reduce the frequency of the common cold, although the positive effects of vitamin C on the duration and severity of the common cold are less certain.

Japanese researchers conducted a double blind, five-year, randomized, controlled trial, with participants diagnosed with atrophic gastritis. Of the 439 eligible subjects, 144 and 161 were assigned to receive 50 mg (low-dose group) or 500 mg (high-dose group) of vitamin C, respectively. During the supplementation phase, 61 dropped out, and 244 completed the trial.

Total number of common colds (per 1,000 person-months) was 21.3 and 17.1 for the low- and high-dose groups, respectively. After adjustment for several factors, the relative risks (95% confidence interval) of suffering from a common cold three or more times during the survey period was 0.34 for the high-dose group. No apparent reduction was seen for the severity and duration of the common cold.

Researchers concluded vitamin C supplementation significantly reduces the frequency of the common cold, but has no apparent effect on duration or severity. The study authors noted, "Considering several limitations due to protocol amendment, the findings should be interpreted with caution."