The review, published in the Open Respiratory Medicine Journal, reports strong evidence that zinc has a beneficial effect on common cold duration, depending on the total dosage of zinc and the composition of lozenges.
“Controlled trials that have examined the effect of zinc lozenges on common cold symptoms have reported divergent results,” said Dr. Harri Hemila of the University of Helsinki, Finland, who authored the review.
“This meta-analysis shows that a large part of the divergence can be explained by the variation in the total daily dose of zinc that the person obtained from the lozenges,” she added.
The common cold is one of the most widespread illnesses in the world. It is estimated that adults suffer from between two to four episodes annually, whilst children in school may have 12 episodes per year.
A recent Cochrane review estimated that the total economic impact of cold-related work loss exceeds $20 billion USD per year. As a result, Americans spend around $2.9 billion on over-the-counter drugs (and another $400 million on prescription medicines) for symptomatic relief of cold.
There is, however, no proven treatment for the common cold. But, as the Cochrane reviewers recently explained, “even a medication that is only partially effective in the treatment and prevention of the common cold could markedly reduce morbidity and economic losses due to this illness.”
Interest in the use of zinc for cold grew following the results of a 1984 trial conducted by Eby (Antimicrobial Agents and Chemotherapy, Vol. 25, No. 1).
Eby’s results suggested that if treatment – consisting of one 23 mg zinc lozenge dissolved in the mouth every second waking hour – commenced within three days of the development of symptoms of a cold, the average duration of symptoms was reduced by about seven days.
Hemila carried out a meta-analysis of all the placebo-controlled trials that have examined the effect of zinc lozenges on natural common cold infections.
Of the 13 trials identified, she identified that five used a total daily zinc dose of less than 75 mg. These five all found no effect of zinc on the common cold.
Hemila reported that three trials using zinc acetate in daily doses of over 75 mg, showed benefit, reducing cold duration by 42 per cent on average.
A further five trials used zinc salts – other than acetate – in daily doses of over 75 mg. Hemilia found these trials reduced cold duration by an average of 20 per cent.
Dr. Hemila concluded that “since a large proportion of trial participants have remained without adverse effects, zinc lozenges might be useful for them as a treatment option for the common cold.”
“The effects of zinc lozenges should be further studied to determine the optimal lozenge compositions and treatment strategies,” she added.
Source: The Open Respiratory Medicine Journal
Volume 5, Pages 51 – 58, Available online here.
“Zinc Lozenges May Shorten the Duration of Colds: A Systematic Review”
Author: Harri Hemilä