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Can Vitamin C cure a cold?

The idea originally came from Nobel prize-winning chemist Linus Pauling in the 1970s. Pauling reported that there was ‘strong evidence’ that vitamin C decreased the incidence of colds. However, his optimistic analysis was based mostly on a small and short randomised study on school children in a skiing school in the Swiss Alps, which reported a significant reduction in the incidence (-45%) and duration (-35%) of colds. It wasn’t a good enough basis to drawn such strong conclusions, but Pauling’s authority made people listen.

You often hear it – if you’re feeling like you’re getting a cold, dose up on vitamin C. But is there any evidence that it works?

So, what’s the real evidence?

Firstly, what about daily vitamin C stopping you getting a cold? Well, in 2013 a review of a lot of different trials and concluded that daily vitamin C had no effect on common cold incidence in the ordinary population, based on 29 trial comparisons involving 11,306 participants.

So, can daily doses make colds less bad when you do get one? The 2013 analysis reported that based on 31 study comparisons with 9745 common cold episodes, regular supplementation had a modest but consistent effect in reducing the duration of common cold symptoms. Regular supplementation trials found that 0.2 g/day or more reduced common cold duration modestly by 8% in adults and by 14% in children and 1 to 2 g/d of vitamin C in children reduced common cold duration by 18%. It’s not much!

Can a big dose once you start feeling a cold coming on help? Studies are inconsistent. One large trial with adults reported benefit from an 8 g therapeutic dose at the onset of symptoms, and two therapeutic trials using five-day supplementation reported benefit, but many others showed nothing – so the evidence is still unclear. And large doses of vitamin C may not be good for you: over 1g per day can cause stomach problems.

Finally, there is some evidence of special circumstances in which vitamin C can help: people exposed to brief periods of severe physical exercise and/or cold environments can, it seems, benefit in terms of both duration and severity of the common cold from regular vitamin C intake above 200mg/day (0.2g), an amount that can easily be consumed as part of a balanced diet. In five trials with 598 participants exposed to short periods of extreme physical stress (including marathon runners and skiers) vitamin C halved the common cold risk. This may have been partly behind the positive results Linus Pauling reported on at a skiing school in the Alps!

If vitamin C doesn’t really help, and you really hate colds, you could consider zinc instead. Some early experiments have suggested that taking zinc lozenges within the first 24 hours of onset of symptoms reduces the duration of the cold. They also reduce the incidence of symptoms persisting beyond 7 days. However, side effects are a bad taste in the mouth and that the dose has to be of >75mg per day. Zinc hasn’t been well studied, though, so do consult your doctor before trying it as some underlying conditions may make it unsuitable for you.