To investigate, researchers reviewed 13 trials with 966 participants who either took zinc or a dummy treatment at the beginning of their symptoms.
Researchers found that people who started taking zinc-loaded lozenges or syrups within 24 hours of showing symptoms such as a sore throat or runny nose, shortened their cold by one day. By comparison, a normal cold lasts about a week.
An earlier review of the literature from 1999 didn't find any signs that zinc supplements would work. But since then several new studies have been completed.
Researchers say further studies are needed, since right now it isn't exactly clear what dose and particular formulation of the supplement will be most helpful, and warn that side effects of too much zinc can include nausea, a bad taste in the mouth, loss of smell, diarrhea, dry mouth and abdominal pain.
The study was published online in The Cochrane Library.
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