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Zinc lozenges may cut the duration of the common cold by more than 40 per cent. But the supplement must contain a certain type of zinc to have a beneficial effect, a new review study suggests.

Since the 1980s, more than a dozen clinical trials have investigated the ability of zinc supplements to limit the sneezing, coughing and congestion of a cold. The results, however, have been mixed.

Now Harri Hemila of the University of Helsinki in Finland has conducted a meta-analysis of 13 placebo-controlled studies and a clear pattern emerges from the review. Some of the trials used a form of the zinc that is not readily available to the body. When it was administered in the form of zinc acetate it appeared to be a highly effective cold fighter.

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Three trials showed a daily dose of zinc acetate greater than 75 milligrams shortened the duration of a cold by 42 per cent – which means the cold lasted about four days instead of the usual seven.

In his study, published online in The Open Respiratory Medicine Journal, Dr. Hemila acknowledged that he is at a loss to explain why sucking on a zinc lozenge can put the breaks on a cold. (It must be dissolved in the mouth rather than swallowed whole.) But if it can shorten the misery of a cold it doesn't really matter how it works, he remarked.

He said additional studies are still needed to determine the ideal dose.

And there's one more catch. A lot of supplements currently on the market don't contain zinc acetate. Dr. Hemila hopes his study, pointing out great differences between lozenges, will encourage supplement manufacturers to introduce new products that are more likely to curb a cold.

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