Results: Total number of common colds (per 1000 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 (CI)) of suffering from a common
cold three or more times during the survey period was 0.34 (0.12–0.97) for the high-dose group. No apparent reduction was
seen for the severity and duration of the common cold.
Conclusion: A randomized, controlled 5-year trial suggests that vitamin C supplementation significantly reduces the frequency
of the common cold but had no apparent effect on the duration or severity of the common cold. However, considering several
limitations due to protocol amendment, the findings should be interpreted with caution