Myth Buster: Vitamin C

Although people still take vitamin C to prevent colds, the evidence is pretty clear that in the general population it has no effect. However, and this is actually a pretty big however, in times of high physical stress it reduces the incidence by 50%.

When we put that together with the fact that 1 in 8 runners get sick immediately after running a marathon we get a pretty clear message: taking vitamin C the week before a race might help prevent you from picking something up there, and if you do may reduce the duration by 1-1.5 days.

This is especially important for runners with multiple races in the build up to their A goal. You don’t want to run a half marathon build up race 6 weeks out then miss the next 2 weeks of training. 

Generally we want to avoid taking vitamins we don’t need (vitamin D in the northern hemisphere during the winter, especially if you have darker skin is an exception). There is actually a slightly lower longevity in habitual multivitamin takers. Further, for runners, taking high doses of any antioxidant can blunt training stimulus. But the week before a race when you are tapering anyway this wouldn’t be an issue. 

So there’s actually pretty good reason to take vitamin C in the lead up to your races.

Source: https://www.cochrane.org/evidence/CD000980_vitamin-c-preventing-and-treating-common-cold