Natural Health News — Oral zinc treatments may shorten the duration of symptoms of the common cold in adults, but a question mark still hangs over whether they are equally effective in children.
Canadian researchers looked at 17 randomised controlled trials with 2121 participants between the ages of 1 and 65 years to determine how effective and safe zinc was in treating the common cold.
All trials were double-blinded and used placebos as well as oral zinc preparations. The authors found that, compared with placebos, zinc significantly reduced the duration of cold symptoms. High doses of ionic zinc (which contains micronised particles of zinc, usually taken as a liquid) were more effective than lower doses at shortening the duration of cold symptoms.
There was say the researchers, some evidence that people taking zinc were less likely to have symptoms after one week, although there was no difference in symptoms between the two groups at three days.
While zinc appeared to reduce the duration of symptoms in adults, in this studythere was no apparent effect in children.
A long history of use
The common cold places a heavy burden on society, accounting for approximately 40% of time taken off work and millions of days of school missed by children each year. The idea that zinc might be effective against the common cold came from a study carried out in 1984, which showed that zinc lozenges could reduce how long symptoms lasted.
Previous studies have shown conflicting effects of zinc in reducing cold symptom severity and the duration of symptoms. Though the weight of the evidence suggests that zinc lozenges are a useful tool in managing the common cold, though scientists always fall short of recommending it was a treatment because they are unclear about exactly how it works (though the same could be said about a number of widely used drugs prescribed regularly by doctors!).
Support from other studies
In the current review, published in the Canadian Medical Association Journal (CMAJ), the authors used a different form of analysis to look at the data. This led them to conclude that zinc had only a weak effect – a conclusion at odd with several previous studies.
For instance, in 2011 a Finnish review found that they could reduce the duration of colds by up to 40%. Earlier in 2011 a review by the prestigious Cochrane Collaboration also concluded that zinc syrup, lozenges or tablets taken within a day of the onset of cold symptoms reduce the severity and length of illness. At seven days, more of the patients who took zinc had cleared their symptoms compared to those who took placebos.
Furthermore in the Cochrane review, children who took zinc syrup or lozenges for five months or longer caught fewer colds and took less time off school. Zinc also reduced antibiotic use in children, which is important because overuse has implications for antibiotic resistance.
In addition the potential side effects of oral zinc were highlighted in the Canadian study. These included leaving a bad taste in the mouth and nausea but no conclusions were drawn as to whether these responses were related to dosage.
Future trials, say the authors, should be designed to help understand the balance between the maximum tolerable doses of bioavailable zinc with consideration toward potential dose-related adverse effects.
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