The Cochrane Reviews are systematic rigorous reviews of the medical literature on medical therapies. Because of the objective and comprehensive methods they use for finding all relevant studies and categorizing them by quality, they are regarded as one of the gospels of evidence based medicine.
Recently the Cochrane Reviews published this review of the medical literature on vitamin C for the prevention and treatment of colds. The study was publicized in this WebMD article. The results are summarized below.
In studies on the general population, taking vitamin C daily year-round did not prevent getting colds but reduced the duration of colds slightly (8% duration reduction in adults, 14% in children). The exception was in studies done under extreme low temperature or extreme physical stress, for example studies on marathon runners, skiers, and soldiers in sub-arctic conditions. In these extreme conditions, daily vitamin C decreased the incidence of colds by about 50%.
In studies that looked at taking vitamin C only once a cold has started, there were no significant differences between vitamin C and placebo.
So, if you take vitamin C only once youâ€™ve caught a cold, you might as well not. To have any benefit, you have to take it preventively every single day, and for that effort you only get an 8% reduction in the duration of a cold. This amounts to a 7 day cold being only 13 hours shorter. For most people, thatâ€™s not really worth it. On the other hand, the authors suggest that if you will be engaging in very strenuous physical activity or exposed to very cold temperatures, daily vitamin C is worth the trouble.
Thanks to David W. for pointing out this letter in the New England Journal of Medicine which documents a rare danger of using earphones outside during a thunderstorm. Ouch! Thereâ€™s no mention of what music he was listening to. I hope it was something great.