The idea that vitamin C supplements can ward off colds is a myth, a major review of the evidence has concluded.

The analysis of data from 30 studies involving more than 11,000 people found no evidence that high doses of the vitamin have any effect against colds for the average person.

The research, conducted by Australian and Finnish scientists, found that extra vitamin C is beneficial only for people under extreme physical stress, such as marathon runners and soldiers, who are 50 percent less likely to catch a cold if they take daily supplements. For people living ordinary lives, any benefits conferred by vitamin C are so small that they would not be worth the effort or expense, the researchers said.

Professor Harri Hemilä, of the University of Helsinki, who led the meta-analysis, said: “It doesn’t make sense to take vitamin C 365 days a year to lessen the chance of a cold."

The analysis appears in the latest issue of The Cochrane Library, published by the research organisation, the Cochrane Collaboration, an international organisation that evaluates medical research.

Scientists pooled information from studies, spanning several decades, that looked at the effect of taking daily supplements of at least 200 milligrams of vitamin C.

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