Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials

Abstract

Background: Results of randomized controlled trials evaluating zinc for the treatment of the common cold are conflicting. We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of zinc for such use.

Methods: We searched electronic databases and other sources for studies published through to Sept. 30, 2011. We included all randomized controlled trials comparing orally administered zinc with placebo or no treatment. Assessment for study inclusion, data extraction and risk-of-bias analyses were performed in duplicate. We conducted meta-analyses using a random-effects model.

Results: We included 17 trials involving a total of 2121 participants. Compared with patients given placebo, those receiving zinc had a shorter duration of cold symptoms (mean difference -1.65 days, 95% confidence interval [CI] -2.50 to -0.81); however, heterogeneity was high (I(2) = 95%). Zinc shortened the duration of cold symptoms in adults (mean difference -2.63, 95% CI -3.69 to -1.58), but no significant effect was seen among children (mean difference -0.26, 95% CI -0.78 to 0.25). Heterogeneity remained high in all subgroup analyses, including by age, dose of ionized zinc and zinc formulation. The occurrence of any adverse event (risk ratio [RR] 1.24, 95% CI 1.05 to 1.46), bad taste (RR 1.65, 95% CI 1.27 to 2.16) and nausea (RR 1.64, 95% CI 1.19 to 2.27) were more common in the zinc group than in the placebo group.

Interpretation: The results of our meta-analysis showed that oral zinc formulations may shorten the duration of symptoms of the common cold. However, large high-quality trials are needed before definitive recommendations for clinical practice can be made. Adverse effects were common and should be the point of future study, because a good safety and tolerance profile is essential when treating this generally mild illness.

Figure 1:

Selection of studies for the qualitative and quantitative analyses. RCT = randomized controlled trial.

Figure 2:

Meta-analysis of the duration of cold symptoms, by age, in randomized controlled trials of oral zinc therapy for the common cold. A value less than zero indicates a benefit from zinc. CI = condifence interval, df = degrees of freedom.

Figure 3:

Meta-analysis of the duration of cold symptoms, by dose of ionic zinc, in randomized controlled trials of oral zinc therapy for the common cold. A value less than zero indicates a benefit from zinc. CI = confidence interval, df = degrees of freedom.

Figure 4:

Meta-analysis of the duration of cold symptoms, by zinc formulation, in randomized controlled trials of oral zinc therapy for the common cold. A value less than zero indicates a benefit from zinc. CI = confidence interval, df = degrees of freedom.

Figure 5:

Meta-analysis of the severity of symptoms in randomized controlled trials of oral zinc therapy for the common cold. A value less than zero indicates a benefit from zinc. CI = confidence interval.

Figure 6:

Meta-analysis of adverse events in randomized controlled trials of oral zinc therapy for the common cold. A risk ratio less than zero indicates a benefit from zinc. CI = confidence interval.