If you're one of the many people who boost your vitamin C intake when you feel a cold coming on, it turns out you're wasting your time. Vitamin C doesn't reduce your risk of catching a cold, nor will it help treat your cold. There is conflicting research about whether or not taking vitamin C can shorten the duration of your cold –- but even if it does, it may not be by much. Some studies find vitamin C supplementation may shorten a cold by about a day while others suggest it's only shortened by a few hours, and yet others find it does nothing at all to shorten a cold's duration. Bottom line? Vitamin C won't hurt you, but it probably won't help your cold -- and beware -- taking too much can cause an upset stomach.