High-Dose Zinc Lozenges May Reduce Duration of Cold Symptoms

Laurie Barclay, MD

August 02, 2011

August 2, 2011 — High-dose, but not low-dose, zinc lozenges shorten the duration of the common cold, according to the results of a meta-analysis reported in the July issue of The Open Respiratory Medicine Journal.

"A number of controlled trials have examined the effect of zinc lozenges on the common cold but the findings have diverged," writes Harri Hemilä, MD, PhD, from the Department of Public Health, University of Helsinki, in Helsinki, Finland. "The purpose of this study was to examine whether the total daily dose of zinc might explain part of the variation in the results."

To identify placebo-controlled trials assessing the effect of zinc lozenges on common cold duration, Dr. Hemilä searched MEDLINE, Scopus, and Cochrane Central Register of Controlled Trials (CENTRAL) databases. All of the identified trials were analyzed together, and the low-dose zinc and high-dose zinc trials were analyzed separately. The Fisher method was used to combine the P values of the trials, and the inverse-variance method allowed pooling of trial data.

The literature search identified 13 placebo-controlled comparisons evaluating the therapeutic effect of zinc lozenges on the duration of common cold episodes of natural origin. The 5 trials using a total daily zinc dose of less than 75 mg found no effect on common cold duration, whereas pooled data from 3 trials using zinc acetate in daily doses exceeding 75 mg showed a 42% reduction in the duration of colds (95% confidence interval [CI], 35% - 48%). The remaining 5 trials used zinc salts other than acetate in daily doses exceeding 75 mg, and pooled analysis of these data showed a 20% reduction in the duration of colds (95% CI, 12% - 28%).

"This study shows strong evidence that the zinc lozenge effect on common cold duration is heterogeneous so that benefit is observed with high doses of zinc but not with low doses," Dr. Hemilä writes. "The effects of zinc lozenges should be further studied to determine the optimal lozenge compositions and treatment strategies."

Limitations of this meta-analysis include those inherent in the included studies.

"On the basis of these long-term studies with high zinc doses, there does not seem to be any basis for assuming that treating the common cold for a week with high doses of zinc in the form of lozenges would cause unanticipated harm," Dr. Hemilä concludes. "A patient suffering from acute adverse effects such as bad taste can simply stop taking the lozenges."

Dr. Hemilä has disclosed no relevant financial relationships.

Open Respir Med J. 2011;5:51-58.

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