Many people have added zinc to their list of home remedies for the common cold, along with chicken soup and honey-lemon tea.
But the jury is out on whether sucking zinc lozenges can loosen a cold's grip. And zinc can cause nausea, not to mention a bad taste in the mouth.
Cold sufferers got excited about zinc in 2013, when an analysis published by the esteemed Cochrane Collaboration (a global network of independent health researchers) found that taking zinc within 24 hours of developing symptoms lessened the duration of the common cold.
But in April this year, Cochrane pulled the review from its database over concerns about some of the data.
A separate 2012 review published in the Canadian Medical Association Journal found that zinc lozenges shaved 1.6 days off the average seven-day cold, but did not reduce the severity of symptoms such as sneezing, coughing and congestion. The best results were associated with zinc acetate, a formulation not normally used in supplements sold in Canadian pharmacies. To reap the benefits, study participants had to suck on a zinc lozenge every two hours except during sleep – about eight lozenges per day.
Some people may be willing to endure the bitter metallic taste of zinc in hopes of cutting a nasty cold short. But taking zinc is not without risk.
Too much zinc, in the form of dietary supplements, may disrupt copper uptake, leading to neurological problems and anemia, according to a study published in June in the Journal of Clinical Pathology.
Health Canada's recommended upper limit for zinc is 40 milligrams per day. Since most zinc lozenges on the market contain between 5 mg and 23 mg of zinc, an adult would reach or exceed the upper limit by sucking on zinc lozenges every two hours to ward off a cold. Additional zinc from food sources (a small steak contains about 10 mg) could push the person well above the upper limit.
The authors of the study on excess zinc noted that short-term use of zinc supplements may not be harmful, according to current evidence. But as a cold remedy, zinc still gets thumbs-down.