The new review published by The Cochrane Collaboration suggests zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms could reduce the severity and length of the illness.
The review of fifteen clinical trials found that after seven days, more patients taking zinc had cleared their symptoms compared to placebo.
“Zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people … When supplemented for at least five months, it [also] reduces cold incidence, school absenteeism and prescription of antibiotics in children,” said the authors led by Meenu Singh from the Post Graduate Institute of Medical Education and Research, India.
“This review strengthens the evidence for zinc as a treatment for the common cold,” said Singh
“However, at the moment, it is still difficult to make a general recommendation, because we do not know very much about the optimum dose, formulation or length of treatment,” he added.
Zinc treatment
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. The authors said that the total economic impact of cold-related work loss exceeds $20 billion 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 reviewers explain, “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.
Singh and colleagues noted that in-vitro assays have indicated that zinc possesses antiviral properties, lending biological plausibility to the results reported by Eby, however, since the trials publication over 25 years ago only a handful of trials shown such beneficial findings.
“The last review of all available RCTs [randomised clinical trials] of zinc for the common cold was published in 1999. Since then, several new studies have been published … It is therefore important to update the information by including all the new clinical trials,” said Singh and colleagues.
Study details
The authors conducted a full literature search for randomised, double-blind, placebo-controlled trials using zinc for at least five consecutive days to treat, or for at least five months to prevent the common cold.
Thirteen therapeutic trials (consisting of 966 participants) and two preventive trials (with 394 participants) were included in the review.
Pooled results from the trials showed that zinc reduced the duration and severity of common cold symptoms when used therapeutically.
Zinc was also reported to reduce the incidence of the common cold, school absence and antibiotic use in healthy children when used as a preventative measure.
Singh and colleagues did however note that people taking zinc lozenges (but not in a syrup or tablet form) are more likely to experience ‘adverse events’ or side effects, including bad taste and nausea.
“Given that some formulations (especially lozenges) produced side effects and not all formulations may be effective, the use of zinc to treat common cold symptoms is presently advised with caution,” they explained.
They added that because there are currently no trials conducted in populations from low income countries; the results of the current review “cannot be applied to people living in low-income countries.”
The reviewers also explained that the use of zinc in people for whom cold symptoms may be troublesome (for example those with chronic illness or immunodeficiency), cannot currently be recommended as there are no studies to suggest benefits in such populations.
Source: The Cochrane Collaboration,
Cochrane Database of Systematic Reviews, doi: 10.1002/14651858.CD001364.pub3.
“Zinc for the common cold”
Authors: M. Singh & R.R. Das