Zinc and the common cold

Zinc lozenges (frequently zinc acetate or zinc gluconate) have been proposed as a treatment for the common cold. The biological mechanism of the effect is not clear, but the benefit of zinc lozenges seems to be caused by local effects in the oropharynx region, since nasal administration of zinc has also shortened the duration of colds.

Research to date has not been conclusive, but has suggested that zinc tablets lessen the symptoms of a cold while causing possible side-effects such as nausea. The benefits of nasal zinc sprays as a cold treatment, as opposed to zinc lozenges, have been described as "very minor".

Zinc has been known for many years to have an effect on cold viruses in the laboratory.

Research into the effect of zinc lozenges on colds between 1984 and 2009 produced a wide range of differing results. It has been hypothesized that these differences were due in part to differences in the lozenges' constituents, mainly the amount of the active ingredient, ionic zinc (iZn). For example, the amount of ionic zinc ranged from 0 to 100%, depending upon the lozenge ingredients in the trials. More recently, the evidence from trials has been reviewed to try and assess the evidence of zinc's effectiveness as a cold cure but the results, while suggestive of a positive effect, have not been conclusive, since no consideration was given to the amount of the active ingredient (iZn) in the lozenges.

In some studies zinc lozenges caused acute adverse effects, such as bad taste, but none of the studies reported long term harm. Furthermore, many of the adverse effects, in particular regarding taste, may be caused by the specific lozenge composition and probably do not reflect the effects of zinc ions themselves. For example, zinc gluconate with dextrose or sugar becomes extremely vile in taste several weeks after manufacture, while zinc acetate dihydrate in a 1:100 mixture with dextrose by weight is permanently pleasant tasting. The most recent trial on zinc acetate found no significant differences between the zinc and placebo groups in the recorded adverse effects with a 92 mg daily dose of zinc.

According to WebMD, there have been several cases of people using zinc nasal sprays and suffering a loss of sense of smell; for this reason the US Food and Drug Administration has issued a warning that people should not use nasal sprays containing zinc.

All reviews to date have suffered from the variability of the studies which have been assessed; future large-scale randomized trials are necessary to determine whether the benefits from zinc treatment for colds outweigh the disadvantages.

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Wikipedia