Vitamin C Prevents Colds
"The popular belief that taking vitamin C, especially at the first sign of a cold, will stop you from getting sick."
This one owes its fame to the Nobel laureate Linus Pauling, who became a vocal advocate for high-dose vitamin C in the 1970s. Large-scale reviews since, including a Cochrane review covering nearly 30 trials and over 11,000 participants, found that regular vitamin C makes no real difference to how often an ordinary person catches a cold. There is a real, if narrower, effect: regular supplementation modestly shortens how long a cold lasts once you have one, and in people under intense short-term physical stress, marathon runners and skiers in the studied trials, it roughly halved the risk of catching a cold at all. Taking vitamin C only after symptoms have already started, the way most people actually use it, showed no consistent benefit in the trials.