A review of 55 studies has shown that even large regular doses of the vitamin do not reduce the risk of contracting a common cold.

People who took daily doses of up to 2g of vitamin C — 33 times more than the recommended daily amount — caught colds at the same rate as those who took an inert placebo instead, the analysis shows.

The findings, by Robert Douglas, of the Australian National University in Canberra, and Harri Hemilä, of the University of Helsinki, suggest that enthusiasm for vitamin C supplements to stave off winter colds is misplaced. “The lack of effect of prophylactic vitamin C supplementation on the incidence of common cold in normal populations throws doubt on the utility of this wide practice,” the authors said.

The scientists did find some evidence that people who took regular vitamin C suffered slightly shorter colds than those who take placebos, though the clinical significance was judged questionable. There was also a preventive effect on people who engage in extreme exertion in cold weather, such as soldiers, skiers and marathon runners, though it was impossible to draw conclusions from this for general health.

Vitamin C became fashion-able as a means of preventing colds in the 1970s, after the Nobel Prizewinning chemist Linus Pauling published his book Vitamin C and the Common Cold. Dr Pauling proposed that large doses of vitamin C would protect against colds and cut their duration.

His advice is followed by millions. It is one of the biggest elements of a supplement market worth £350 million a year in Britain.

Evidence for the preventive worth of vitamin C, however, has always been sparse, and the new survey suggests that such an effect does not actually exist.

Dr Douglas and Dr Hemilä undertook the investigation for the Cochrane Review, which attempts to combine the evidence from many high-quality studies to provide an overall picture of which medical treatments work. Their findings appear today in the journal Public Library of Science Medicine.

They identified 55 controlled studies of sufficient rigour, of which 23 dealt explicitly with vitamin C supplements and cold prevention. For the general population, they found that this regime brought no benefits. Vitamin C is also little use for stopping a cold, the review suggests: in seven studies, no consistent benefit was found.

One of the trials, however, did find that a very large dose of vitamin C — of 8g — on the first day of cold symptoms appeared to shorten its duration. Those results, the scientists said, were “tantalising and deserve further investigation”.

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