The common cold is often caused by the rhinovirus. It is one of the most widespread illnesses and is a leading cause of visits to the doctor and absence from school and work. Complications of the common cold include ear infection, sinusitis and exacerbations of reactive airway diseases. There is no proven treatment for the common cold. However, an even partially effective treatment for treating and preventing the common cold could markedly reduce the health problems and economic losses associated with it.
Zinc inhibits replication of the virus and has been tested in trials for treatment of the common cold. This review identified 18 randomised controlled trials, enrolling 1781 participants of all age groups, comparing zinc with placebo (no zinc). We found that zinc (lozenges or syrup) reduces the average duration of the common cold in healthy people, when taken within 24 hours of onset of symptoms. In people taking zinc their cold symptoms are also less likely to persist beyond seven days of treatment. Prophylactic zinc supplementation for at least five months reduces incidence, school absences and prescription of antibiotics for children with the common cold, although antibiotics are not required for the common cold. People in whom common cold symptoms might be troublesome (for example, those with underlying chronic illness, immunodeficiency, asthma, etc.) have not been studied, so the use of zinc cannot currently be recommended for them. Given the variability in the dose, formulation and duration of zinc use in the included studies, more research is needed to address these before zinc use can be generally recommended for the common cold. However, as the zinc lozenges formulation has been widely studied, and there is a significant reduction in the duration of cold at a dose of ≥ 75 mg/day, for those considering using zinc it would be best to use it at this dose throughout the cold. When using zinc lozenges (not as syrup or tablets) the likely benefit has to be balanced against side effects, notably a bad taste and nausea. Regarding prophylactic zinc supplementation, currently no firm recommendation can be made because of insufficient data.