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Meta-Analysis
. 2015 Feb 25:16:24.
doi: 10.1186/s12875-015-0237-6.

The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis

Harri Hemilä  1 , Elizabeth Chalker  2
Affiliations
Meta-Analysis

The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis

Harri Hemilä et al. BMC Fam Pract. .

Abstract

Background: A previous meta-analysis found that high dose zinc acetate lozenges reduced the duration of common colds by 42%, whereas low zinc doses had no effect. Lozenges are dissolved in the pharyngeal region, thus there might be some difference in the effect of zinc lozenges on the duration of respiratory symptoms in the pharyngeal region compared with the nasal region. The objective of this study was to determine whether zinc acetate lozenges have different effects on the duration of common cold symptoms originating from different anatomical regions.

Methods: We analyzed three randomized trials on zinc acetate lozenges for the common cold administering zinc in doses of 80-92 mg/day. All three trials reported the effect of zinc on seven respiratory symptoms, and three systemic symptoms. We pooled the effects of zinc lozenges for each symptom and calculated point estimates and 95% confidence intervals (95% CI).

Results: Zinc acetate lozenges shortened the duration of nasal discharge by 34% (95% CI: 17% to 51%), nasal congestion by 37% (15% to 58%), sneezing by 22% (-1% to 45%), scratchy throat by 33% (8% to 59%), sore throat by 18% (-10% to 46%), hoarseness by 43% (3% to 83%), and cough by 46% (28% to 64%). Zinc lozenges shortened the duration of muscle ache by 54% (18% to 89%), but there was no difference in the duration of headache and fever.

Conclusions: The effect of zinc acetate lozenges on cold symptoms may be associated with the local availability of zinc from the lozenges, with the levels being highest in the pharyngeal region. However our findings indicate that the effects of zinc ions are not limited to the pharyngeal region. There is no indication that the effect of zinc lozenges on nasal symptoms is less than the effect on the symptoms of the pharyngeal region, which is more exposed to released zinc ions. Given that the adverse effects of zinc in the three trials were minor, zinc acetate lozenges releasing zinc ions at doses of about 80 mg/day may be a useful treatment for the common cold, started within 24 hours, for a time period of less than two weeks.

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Figures

Figure 1
Figure 1
The effect of high dose zinc acetate lozenges on the duration of the common cold. In the forest plot on the right side, the vertical line indicates the placebo level. The horizontal lines indicate the 95% CI for the zinc effect and the squares in the middle of the horizontal lines indicate the point estimate of the effect in the particular trial. The sizes of the squares indicate the relative weights of the trials. The diamond shape indicates the pooled effect and the 95% CI. The pooled effect was −42% (95% CI: −35% to −48%; P = 10−33). The duration of colds was transformed to the relative scale so that the duration in the respective placebo group was given the value of 100%. Thus the difference between zinc and placebo groups directly indicates the effect of zinc lozenges in percentages. See Additional file 2 for the extraction of data and for the calculation of the relative mean and SD values for total common cold duration.
Figure 2
Figure 2
The effect of high dose zinc acetate lozenges on the duration of respiratory symptoms of the common cold. In the forest plots on the right side, the vertical line indicates the placebo level. The horizontal lines indicate the 95% CI for the zinc effect and the square in the middle of the horizontal line indicates the point estimate of the effect in the particular trial. Arrows at the end of the horizontal lines indicate that the 95% CI extends out of the forest plot. The sizes of the squares indicate the relative weights of the trials. The diamond shape indicates the pooled effect on the symptoms and its 95% CI. The duration of symptoms was transformed to the relative scale, thus the duration in the respective placebo group was given the value of 100%. The difference between zinc and placebo groups thus directly indicates the effect of zinc lozenges in percentages. See Additional file 2 for the extraction of data and for the calculation of the relative mean and SD values for the duration of symptoms, and Additional file 3 for the raw data and the estimates for individual studies.
Figure 3
Figure 3
The effect of high dose zinc acetate lozenges on the duration of systemic symptoms of the common cold. In the forest plots on the right side, the vertical line indicates the placebo level. The horizontal lines indicate the 95% CI for the zinc effect and the square in the middle of the horizontal line indicates the point estimate of the effect in the particular trial. Arrows at the end of the horizontal lines indicate that the 95% CI extends out of the forest plot. The sizes of the squares indicate the relative weights of the trials. The diamond shape indicates the pooled effect on the symptoms and its 95% CI. The duration of symptoms was transformed to the relative scale, thus the duration in the respective placebo group was given the value of 100%. The difference between zinc and placebo groups thus directly indicates the effect of zinc lozenges in percentages. See Additional file 2 for the extraction of data and for the calculation of the relative mean and SD values for the duration of symptoms, and Additional file 3 for the raw data and the estimates for individual studies.
Figure 4
Figure 4
The effect of high dose zinc acetate lozenges on the duration of common cold symptoms. The pooled estimates and their 95% CIs are shown in this figure. The horizontal lines indicate the 95% CI for the effect and the squares in the middle of the horizontal lines indicate the point estimates of the effect on the particular respiratory and systemic symptoms. See Additional files 2 and 3 for the calculations.
Figure 5
Figure 5
The duration of the specific symptom as a proportion of the total common cold duration (set as 100%) of the placebo groups. The left side of the figure shows the duration of the symptom as a proportion of the total common cold duration, and the right side shows the same information as a forest plot. On the scale of this figure, 100% corresponds to the total duration of the common cold of the placebo groups. The duration of symptoms was calculated as follows. First, the duration of the specific symptom was calculated as the percentage of the total common cold duration for the placebo group (5.1 days in Petrus et al. [21], 8.1 days in Prasad et al. (2000) [22], and 7.1 days in Prasad et al. (2008) [23]). Then the relative duration of each specific symptom was pooled using the RevMan program. There was no heterogeneity between the three trials in the relative duration of untreated nasal discharge, sneezing, sore throat, hoarseness, muscle pain, headache, and fever with P > 0.05 for the test of heterogeneity. The relative durations of untreated nasal congestion (I2 = 85%), scratchy throat (I2 = 74%), and cough (I2 = 68%) were significantly different in the three trials. See Additional files 2 and 4 for the calculations.
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