Plain language summary
Zinc lozenges are sometimes used to reduce the symptoms of the common cold. However studies have had varying results, possibly due to using different doses, as well as different forms of zinc. The aim of this meta-analysis was to compare the efficacy of zinc acetate lozenges with zinc gluconate lozenges in reducing the duration of the common cold and to examine the dose-dependency of the effect. The study authors looked at seven randomised trials with 575 participants with common colds. All of the trials were placebo-controlled and used zinc doses of over 75 mg/day. Three of the trials used zinc lozenges composed of zinc acetate, and four used zinc gluconate. Overall, zinc lozenges reduced cold duration by 33% compared to a placebo. The trials that used lozenges composed of zinc acetate found that colds were shortened by 40% and zinc gluconate reduced duration by 28%. The difference between the two forms was not statistically significant. Five trials used zinc doses of 80–92 mg/day, and common cold duration was reduced by 33%. Two trials used zinc doses of 192–207 mg/day and found an effect of 35%. The difference was not statistically significant. The authors concluded that zinc gluconate lozenges are equally as effective as zinc acetate lozenges. There is no evidence that zinc doses over 100 mg/day are more effective in reducing the duration of the common cold.
Abstract
OBJECTIVE To compare the efficacy of zinc acetate lozenges with zinc gluconate lozenges in common cold treatment and to examine the dose-dependency of the effect. DESIGN Meta-analysis. SETTING Placebo-controlled zinc lozenge trials, in which the zinc dose was > 75 mg/day. The pooled effect of zinc lozenges on common cold duration was calculated by using inverse-variance random-effects method. PARTICIPANTS Seven randomised trials with 575 participants with naturally acquired common colds. MAIN OUTCOME MEASURE Duration of the common cold. RESULTS The mean common cold duration was 33% (95% CI 21% to 45%) shorter for the zinc groups of the seven included trials. Three trials that used lozenges composed of zinc acetate found that colds were shortened by 40% and four trials that used zinc gluconate by 28%. The difference between the two salts was not significant: 12 percentage points (95% CI: -12 to + 36). Five trials used zinc doses of 80-92 mg/day, common cold duration was reduced by 33%, and two trials used zinc doses of 192-207 mg/day and found an effect of 35%. The difference between the high-dose and low-dose zinc trials was not significant: 2 percentage points (95% CI: -29 to + 32). CONCLUSIONS Properly composed zinc gluconate lozenges may be as effective as zinc acetate lozenges. There is no evidence that zinc doses over 100 mg/day might lead to greater efficacy in the treatment of the common cold. Common cold patients may be encouraged to try zinc lozenges for treating their colds. The optimal lozenge composition and dosage scheme need to be investigated further.
Methodological quality
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