The outcome of a meta-analysis published online on June 23, 2001 in the Open Respiratory Medicine Journal concludes that zinc lozenges are beneficial in reducing the length of the common cold if the mineral is available in sufficient quantities.
For the review, Dr Harri Hemilä of the University of Helsinki selected thirteen placebo-controlled trials examining the effects of zinc lozenges on cold duration. Three trials tested zinc acetate and five trials tested other forms of zinc in daily doses of greater than 75 milligrams. The remaining five trials evaluated the use of lozenges that contained lower doses of the mineral.
While pooled analysis of the five trials that analyzed the effects of less than 75 milligrams zinc found no benefit, zinc acetate consumed in doses higher than 75 milligrams per day was associated with a 42 percent reduction in cold duration. Consuming more than 75 milligrams per day of other forms of zinc was associated with a 20 percent decrease in the length of colds.
Dr Hemilä notes that consideration of dosage alone may be a simplified approach to supplementation, because some types of zinc lozenges, including those that contain zinc tartrate or citrate, bind zinc ions tightly, thereby decreasing the level of free zinc ions. Additionally, some brands of lozenges may contain ingredients such as cotton seed oil that can react with zinc ions to create insoluble compounds. “New trials should be carried out to confirm the benefit of zinc acetate lozenges at a dosage of about 80 mg per day, and to examine whether even lower daily doses in appropriately formulated lozenges might be effective,” Dr Hemilä writes.
Although no long term adverse effects were observed, high doses of zinc consumed for extended periods of time are not recommended. Nevertheless, Dr Hemilä remarks that 150 milligrams per day zinc has been administered for therapeutic uses for months or years in specific patients, and that a trial involving six weeks of supplementation at this level failed to result in a deficiency of copper (a potential side effect of prolonged intake of high amounts of zinc).
“Since a large proportion of trial participants have remained without adverse effects, zinc lozenges might be useful for them as a treatment option for the common cold,” Dr Hemilä writes. “More research is needed on zinc lozenges to find optimal lozenge compositions and treatment strategies.”