Lozenges that contain zinc can shorten the duration of common colds by a third, according to researchers from Finland, who suggest patients should be encouraged to take them.
They specifically set out to look for any differences between zinc acetate lozenges and zinc gluconate lozenges regarding their efficacy in shortening the duration of common colds.
“Common cold patients may be encouraged to try them for treating their colds”
However, they concluded there was no significant difference between the two types of zinc lozenge, after analysing the results of seven randomised trials.
They found that the duration of colds was shortened on average by 33% by both types.
In the meta-analysis, by researchers from the University of Helsinki, collected trials on zinc acetate and zinc gluconate lozenges and compared their observed efficacies.
Three trials had used zinc acetate lozenges and found that colds were shortened on average by 40%, while four trials 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, said the study authors in the Journal of the Royal Society of Medicine Open.
In addition, they noted one of the zinc gluconate lozenge trials was an outlier inconsistent with all the other six zinc lozenge trials.
If that trial was excluded, the difference between the three zinc acetate and the three zinc gluconate trials shrunk to just 2% – equivalent to a 40% versus 38% reduction in common cold duration.
Therefore, properly composed zinc gluconate lozenges may be as effective as zinc acetate lozenges, said the researchers.
They also analyzed 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 80-92 mg of zinc per day and the two trials that used 192-207mg of zinc per day. Thus, zinc doses of over 100mg per day do not seem to provide any more benefit.
Study author Dr Harri Hemilä said there is no justification for the popular phrase that “there is no cure for the common cold” because of the strong evidence that zinc lozenges can shorten duration by over 30%.
But he noted that the “optimal lozenge composition and dosage scheme need to be investigated further”.
“The optimal composition of zinc lozenges should be investigated in addition to the optimum frequency of their administration,” he said.
“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 stated.
Zinc lozenges appear to influence the common cold through the release of free zinc ions into the oro-pharyngeal region.
However, previously zinc lozenges containing citric acid have been shown to be ineffective in treating colds, because citric acid binds zinc ions very tightly and no free zinc is released.
“Patients should ascertain that the lozenges do not contain citric acid or its salt citrate,” added Dr Hemilä.