Vitamin C Against Infections? For Men Only!

Researchers (Constantini. 2010) from the University medical center in Jerusalem found that contrary to popular believe, vitamin C will not help ward off the common cold in swimmers. Interestingly, they did observe a positive effect on severity and duration of infection in males, only:

The duration of respiratory infections was 22% shorter in vitamin C group, but the difference was not statistically significant. However, we found a significant interaction between vitamin C effect and sex, so that vitamin C shortened the duration of infections in male swimmers by 47% (95% CI: -80% to -14%), but had no effect on female swimmers (difference in duration: +17%; 95% CI: -38% to +71%). The effect of vitamin C on the severity of URIs was also different between male and female swimmers, so that vitamin C was beneficial for males, but not for females.

Hitherto, the scientists have no explanation for the observed gender bias. It could however have contributed to the equivocal  results of previous studies, where positive effects on duration and severity of upper respiratory tract infections occurred in some, yet not in other studies.