According to a meta-analysis published in the Journal of the Royal Society of Medicine Open, seven randomised trials with zinc acetate and zinc gluconate lozenges found that the duration of colds was shortened on average by 33%.
Zinc acetate has been widely proposed as the most ideal salt for zinc lozenges since acetate binds to zinc ions very weakly. Zinc gluconate is another salt that has been frequently used in zinc lozenges but it binds the zinc ion more tightly.
However, it was not known if this caused significant differences when it came to treating common colds.
In the meta-analysis, three trials had used zinc acetate lozenges and found that colds were shortened on average by 40%.
Four trials had used zinc gluconate lozenges and colds were shortened on average by 28%. The 12% difference between the average effects of the two kinds of lozenges was explained purely by random variation.
Study author Dr Harri Hemilä from the University of Helsinki also analysed the dose response relationship between the elemental zinc dose and the observed efficacy in reducing common cold duration.
There was no difference in the efficacy between five trials that used 80 to 92 mg of zinc per day and the two trials that used 192 and 207 mg of zinc per day. Thus, zinc doses of over 100 mg per day do not seem to provide any more benefit.
Writing in the journal, Dr Hemilä concluded: “The trials included in this study were of high methodological quality: randomised, double-blind, and placebo-controlled. They were carried out over three decades by six different research groups. The evidence is thus very strong that zinc lozenges may shorten the duration of colds by approximately 33%.
“The optimal composition of zinc lozenges should be investigated in addition to the optimum frequency of their administration. Nevertheless, the current evidence of efficacy for zinc lozenges, in particular zinc acetate lozenges, is so strong that common cold patients may be encouraged to try them for treating their colds.”
He added patients should ascertain that the lozenges do not contain citric acid or its salt citrate because previous studies have found these inhibit the release of zinc.
Source: JRSM Open
Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage
Author: Harri Hemilä