Does an Orange a Day Keep the Doctor Away?
When it comes to health and nutrition, there are so many myths and superstitions out there that it can be hard to keep straight what is actually true, even if you're a reasonably skeptical person. A while back I discovered that an idea I'd long accepted, that drinking milk will make a cold worse, is one such myth. Now I've discovered another: The notion that taking vitamin C will fight off a cold is a myth. It's not just unsubstantiated, like a lot of health myths, rather there's actually a lot of evidence against the idea.
Apparently the notion that vitamin C helps with the cold was popularized by a book written by Nobel-prize-winning chemist Linus Pauling, but he doesn't seem to have had much evidence. Since then there's been a lot of research concerning the effects of vitamin C on the cold, including a number of meta-studies systematically reviewing the research in the literature. Taken together, what the research shows is that taking vitamin C has no benefit for preventing colds in normal situations*, nor does it reduce the severity of symptoms. Some research did show a small (but statistically significant) reduction in the duration of colds (by about 10%, which probably isn't of much practical significance). With more than 30 studies, these facts seem pretty well established, but apparently the idea just won't die.
I guess the upside is that vitamin C is something you need anyway, and it's a water-soluble vitamin, so taking moderate extra amounts of vitamin C seems like it should be relatively harmless. Apparently taking excessively large amounts can have side-effects like diarrhea and kidney stones.
The sources I'm drawing all this from are the Mayo Clinic, a short Newsweek article, and a much more detailed article over at Quackwatch.
* There is reportedly some research that suggests vitamin C may have a significant ability to prevent colds in people who are in situations of high physical stress such as soldiers, marathon runners, etc.