IntroductionThe Republic of Korea (ROK) military has a high incidence of respiratory diseases at training centres. Vitamin C has been reported to reduce the incidence of colds. For the purpose of preventing soldiers' respiratory diseases, this study aimed to investigate whether vitamin C intake can prevent common colds in the ROK Army soldiers.MethodsThis was a randomised, placebo-controlled, and double-blind trial of soldiers who enlisted in the Korea Army Training Centre for 30 days from 12 February to 13 March 2018. The study participants were divided into groups (vitamin C vs placebo). The military medical records were searched to determine whether the participants had a common cold. Multiple logistic regression analysis was performed to identify the association between vitamin C intake and diagnosis of common colds. In addition, subgroup analysis on the relationship between vitamin C intake and common cold according to smoking status, training camp and physical rank was conducted.ResultsA total of 1444 participants were included in our study. Of these participants, 695 received vitamin C (6000 mg/day, vitamin C group), while 749 participants received placebo (0 mg/day, placebo group). The vitamin C group had a 0.80-fold lower risk of getting a common cold than did the placebo group. Subgroup analyses showed that this effect was stronger among subjects in camp A, among never smokers and among those in physical rank 3.ConclusionVitamin C intake provides evidence to suggest that reducing the common colds in Korean Army soldiers. Our results may serve as a basis for introducing military healthcare policies that can provide vitamin C supplementation for military personnel in basic military training.