Zinc Appears to Reduce Cold Symptoms: Cochrane Review
Lee Swanson Research Update
The new review, published by The Cochrane Collaboration suggests zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms could reduce the severity and length of illness.
Looking at 15 clinical trials, the review found that after seven days, more patients taking zinc had cleared their symptoms compared to placebo.
"Zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people. When supplemented for at least five months, it [also] reduces cold incidence, school absenteeism and prescription of antibiotics in children," said the authors led by Meenu Singh from the Post Graduate Institute of Medical Education and Research, India.
"This review strengthens the evidence for zinc as a treatment for the common cold," Singh said. "However, at the moment, it is still difficult to make a general recommendation, because we do not know very much about the optimum dose, formulation or length of treatment."
There is no proven treatment for the common cold. But, as the reviewers explain, "even a medication that is only partially effective in the treatment and prevention of the common cold could markedly reduce morbidity and economic losses due to this illness."
Interest in the use of zinc for colds grew following the results of a 1984 trial conducted by Eby (Antimicrobial Agents and Chemotherapy, Vol. 25, No. 1). Eby’s results suggested that if treatment—consisting of one 23 mg zinc lozenge dissolved in the mouth every second waking hour—commenced within three days of the development of symptoms of a cold, the average duration of symptoms was reduced by about seven days.
Singh and colleagues noted that in-vitro assays have indicated that zinc possesses antiviral properties, lending biological plausibility to the results reported by Eby. However, since the trial's publication over 25 years ago only a handful of trials have shown such beneficial findings.
"The last review of all available RCTs (randomized clinical trials) of zinc for the common cold was published in 1999. Since then, several new studies have been published. It is therefore important to update the information by including all the new clinical trials," Singh and colleagues said.
The authors conducted a full literature search for randomized, double-blind, placebo-controlled trials using zinc for at least five consecutive days to treat, or at least five months to prevent the common cold.
Thirteen therapeutic trials (consisting of 966 participants) and two preventive trials (with 394 participants) were included in the review. Pooled results from the trials showed that zinc reduced the duration and severity of common cold symptoms when used therapeutically.
Zinc was also reported to reduce the incidence of the common cold, school absence and antibiotic use in healthy children when used as a preventative measure.
The Cochrane Collaboration, Cochrane Database of Systematic Reviews Published online.
March, 2011
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