Zinc is widely recognized as being beneficial to common cold symptoms. But University of Helsinki researchers hypothesised that the beneficial effects of zinc acetate lozenges may be limited because they dissolve in the mouth, meaning that the zinc ions remain concentrated in the localised throat area.
However when the researchers, led by Harri Hemila, pooled data from three randomised double-blind, placebo-controlled trials, they found that this was not the case.
High dose lozenges shortened the duration of several common cold symptoms, including muscle ache by 54%, coughs by 46%, nasal congestion by 37% and a scratchy throat by 33%. There was no difference in the duration of headache and fever.
“The most common cause for the common cold is rhinovirus, and usually the most bothersome symptom of rhinovirus infections is nasal discharge," the researchers wrote. "Therefore the 34% reduction in the duration of nasal discharge, with no heterogeneity between the three trials, is a particularly important effect.
“The common cold is the most common cause of acute cough and therefore the estimated 46% reduction in the duration of cough is also very important.”
They said the benefits are only seen with relatively high doses of zinc from 80 to 90 mg/day, taken within 24 hours of symptoms appearing and for a period of less than two weeks.
A 2014 European Food Safety Authority scientific panel reviewed the population reference intakes (PRI) for zinc and ruled that levels for adults range from 7.5 to 12.7 mg/day for women and 9.4 to 16.3 mg/day for men.
While an 80 mg dose is substantially higher than the EFSA recommended limit, the researchers say it is unlikely to cause serious adverse side effects if taken for a short time.
However, they also say that the lack of high dose lozenges on the market means that cold sufferers may have difficulty in obtaining the benefits.
“Many zinc lozenges on the market either have too low a dose of zinc or contain ingredients that tightly bind to zinc ions, such as citric acid. Therefore, the full benefit seen in the three high dose zinc acetate trials may not be easy to actualise until high dose zinc acetate lozenges are more widely available on the market.”
Zinc has 18 EFSA-approved health claims - the highest number for a mineral - including authorisations for the maintenance of a normal immune system, protein synthesis, healthy skin and nails and the maintenance of healthy bones. In comparison, calcium has 10 approved claims while iron has 12.
A 2013 Cochrane review further boosted the mineral’s solid reputation by suggesting that supplementation of iron, zinc and vitamin A for infants between the age of six months and one year can reduce the risk of anaemia.
Source: BMC Family Practice
Published 5 February 2015, doi:10.1186/s12875-015-0237-6
'The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis'
Authors: Harri Hemilä and Elizabeth Chalker