Does vitamin C help a cold?

If your first instinct upon developing the sniffles is to reach for the citrus or a bottle of vitamin C then you are in good company. The theory that vitamin C could ward off the common cold was championed in the 1970s by chemist Linus Pauling, recipient of not one but two Nobel Prizes. The idea caught on but, while it would be rash to say vitamin C is totally ineffective against colds, the evidence in so far doesn’t support Pauling’s high hopes.

For a start, it doesn’t help to up your vitamin C intake once you already have a cold. Daily supplements throughout the year can reduce the duration of colds slightly (something like 10%), and perhaps their severity, too. These preventative supplements don’t prevent colds, though, just diminish their strength, and the tiny benefit hardly justifies vitamin C’s reputation as a cold-stopper.

Things aren’t entirely clear cut. Many different variables may impinge on the results, and only a few can be explored at a time. Some reliable studies indicate that vitamin C really does prevent colds in people who have been stressed by exertion or cold. There are tantalising results hinting at other exceptions that could have slipped past the big studies, and there are bound to be yet others that haven’t been examined at all.

Those who believe in vitamin C for treating colds — and there are many of them — argue that the doses studied so far are inadequate. They may be right. Research has focussed on doses several times the recommended daily allowance (RDA), up to and exceeding those you get from vitamin pills. But perhaps you need dozens, or hundreds of times the RDA to prevent a cold. Or perhaps you need to deliver it more frequently, or in a different form, or...

You can see why scientists are so fond of saying more research is needed: it’s not just to ensure their grants get renewed. What does seem sure is that, unless you’ve just run a marathon, typical supplements of vitamin C aren’t going to do much for a cold.

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