Vitamin C and Infections.

Plain Language Summary

This article reviews the available literature on the effect of vitamin C on infections. In the early 20th century scurvy was found to be due to vitamin C deficiency and it was also observed that lack of vitamin C predisposed to infections, in particular pneumonia, which sparked interest in the connection between vitamin C and infections. Infections increase oxidative stress which may lead to a decrease in plasma levels of vitamin C, which has antioxidant properties, and much higher intakes of vitamin C may be necessary to maintain sufficiently high plasma levels during an infection. In animal studies vitamin C has been found to be beneficial against various infectious agents including bacteria, viruses, Candida albicans, and protozoa. The common cold is the most widely studied infection with regards to vitamin C. Vitamin C supplementation has been shown to only decrease the incidence of the common cold in specific subgroups but not the population as a whole. However, supplementing no less than 1g vitamin C per day significantly shortened the duration and alleviated severity of colds. Interpretation of studies is complicated by a number of factors, including dose of vitamin C, with up to a 240-fold difference between the lowest and highest vitamin C supplementary dose used in the common cold trials. This review also discusses why interest in the vitamin C/common cold research plummeted in the mid-1970s. Studies on vitamin C and pneumonia showed benefits, but as all these trials were done in specific population groups, the results cannot necessarily be generalised. There is insufficient clinical research into the use of vitamin C for other infections. The author concludes that in view of vitamin C being safe and cheap even modest clinical effects are worth exploring.