Thursday, February 21, 2008

Fact or Fiction: Vitamin C and the Common Cold

Today's issue of the Ottawa Metro features an article extolling the virtues of vitamin C as cold killer. This is a common piece of folk wisdom that we've touched upon briefly before. Is there truth behind the vitamin C advice?

It turns out the subject is quite controversial, with many people preaching the value of vitamin C in cold prevention. The science, however, is less clear. Several studies have been done to examine the effects of vitamin C on the cold prevention and treatment. One meta-analysis of these studies showed that vitamin C has no effect on the incidence of the common cold and slight but variable effects on duration and severity. From the summary:
"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."
One of the authors of this review has since argued that therapeutic vitamin C treatment (i.e. treatment after onset of symptoms) may be beneficial in children. Some studies have shown similar modest (but statistically insignificant) effects, while others none at all. Overall the evidence for therapeutic vitamin C use is unconvincing. The NIH has a detailed page describing vitamin C usage, that has the following to say about cold treatment:
"More than 30 clinical trials including more than 10,000 participants have examined the effects of taking daily vitamin C on cold prevention. Overall, no significant reduction in the risk of developing colds has been observed. [...] Numerous studies have examined the effects of starting vitamin C after the onset of cold symptoms. Overall, no significant benefits have been observed. Initial evidence from one study reports possible benefits with high doses of vitamin C taken at the onset of symptoms, but without additional evidence this remains indeterminate. At this time, the scientific evidence does not support this use of vitamin C."
On both cold prevention and cold treatment, the NIH gives vitamin C a grade of D meaning "fair scientific evidence against this use." It is interesting to note, however, that vitamin C does seem to have an effect in people living in extreme circumstaces such as soldiers in sub-arctic exercises or marathon runners. Overall, for the general public, vitamin C is important for health but the evidence does not support its use in cold prevention or treatment.


The Doc said...

I was reading that this morning and wondering exactly what the nutritional expert was basing this on.

The Doc said...

Actually, I got slightly angrier towards the end of the article, where she also promoted drinking vitamin c because it would help flush things out of your system... because it's water soluble.

Won't it get flushed out if it's water soluble, and roughly how much should I consume to be sure that all of what I am flushing is flushed?

kamel said...

Yeah, I didn't get that part either. The only info I could find about 'flushing your system' was from a bunch of wellness sites that offer no evidence or proper explanation.

Actually excess vitamin C does get flushed out in the urine. The plasma levels are maintained at 160uM or less (certain tissues have up to 100x more) and the rest hits the kidney then the toilet. (from wikipedia)

The Doc said...

I would expect nothing less from a water soluble metabolite like that.

Ever take a Vitamin B tablet? Always good for fluorescent urine. Why would vitamin C be any different?

Z said...
This comment has been removed by the author.
Z said...

ok, i guess i'll regret mentioning this, but here's a girl who eats a c-vitamin pill every day because of superstition:

I'm thinking: Maybe it's delaying the growth of grey hairs (i'm 33). I have have, of course, no proof.
I seem to lose less straws like this (less to clean up in the bathroom)

As regards the cold prevention: i think, no: i always get colds, whether i eat the pills or not. Maybe fruit consumption is better.

Nice post!

Michael said...

Taking Vitamin C after getting a cold never did much for me except give me an upset stomach. Instead, I started getting my Vitamin C daily (as in EVERY day) from a 12 oz glass of orange juice and a multivitamin. The result was no cold for over 13 months! And before this I was getting at least 3 colds a year. See my post about my Vitamin C experience at My Health Blog.

Note that I run 4 mi every other day in outside temps below zero on occasion - this may be why I was getting so many colds before. At any rate, I am a big believer in regular natural Vitamin C intake. No need for the Vitamin C supplements in my experience.

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