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What does vitamin C really do?

July 14, 2009

Today, I had an interesting article pop up on my google news custom search page: “Boost your immune system with Vitamin C” which claims

Vitamin C is at the top of the list among natural immune boosters for your body. The research on the immune boosting properties of the vitamin has been extensive. Your body’s immune system offers protection against a host of viruses as well as health ailments. It is of paramount importance that your body’s immunity be enhanced in order to increase its ability to ward off diseases. When your body has a weak immune system is becomes vulnerable to viruses resulting in you getting sick. The best way to give a boost to your immune system is by improving the nutritional value of your diet.

I’ll admit that when I get a cold, I take supplements with large doses of vitamin C and I increase my consumption of things like orange juice. The conventional wisdom that vitamin C is useful is so ingrained that I never thought to question it. But the fact that this article was published in “The Alternative Health Journal” made me immediately skeptical, so I decided to actually take a look at what the science has to say.

Vitamin C or ascorbic acid was originally isolated as the key component of a diet to prevent scurvy. Most animals are able to synthesize it on their own, but humans belong to a small list of creatures that must consume it as part of their diet. Early research showed that in animals that produce their own vitamin C, produce far more (especially under stress conditions) than a typical person will consume as part of their diet, which sparked interest in supplementing the human diet with larger doses.

In 1970, Linus Pauling, a very well-respected chemist published a book called “Vitamin C and the Common Cold,” in which he compared several previous studies and concluded that high doses of vitamin C led to decreased incidence of colds and to less severe colds. Since then, several animal studies have show that vitamin C does in fact contribute to the fight against several types of pathogens. So there you have it; case closed, right?

Not so fast. A recent article [you might need special permissions for this link] published in 2007 combined data from several independent placebo-controlled studies and concluded

regular ingestion of vitamin C has no effect on common cold incidence in the ordinary population. It reduced the duration and severity of common cold symptoms slightly, although the magnitude of the effect was so small its clinical usefulness is doubtful. […]

Trials of high doses of vitamin C administered therapeutically (starting after the onset of symptoms), showed no consistent effect on either duration or severity of symptoms.

So much for the conventional wisdom. It seems statements like

Vitamin C has been proven to be the most potent vitamin to increase your body’s immunity

and

Vitamin C helps your immune system in two major ways. It rids your body of the foreign invaders and helps it to detect any sign of tumor in your body.

might be a bit over blown.

Still, this analysis still showed there may be a significant benefit to large doses of vitamin C as a prophylactic in subjects that had undergone some type of extreme stress (like exercise or cold temperature), and the authors admitted that there were not enough trials done to accurately measure its effect when used as a treatment after onset of symptoms, so it’s clear there’s a lot more to understand.

Large doses of vitamin C do not seem to have any significant downsides, so until more research it done, it certainly doesn’t hurt to supplement it when you have a cold. Just don’t expect it to be a panacea.

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One Comment leave one →
  1. July 25, 2009 9:48 am

    Another bit of “common wisdom” about Vitamin C (well… it was common in the drug-user’s world at one point, I don’t know about now) was that while on hallucinogens one could increase the potency of one’s “trip” if you consumed large doses of Vit. C. Would be interesting to know if there’s any actual truth in such a statement…

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