Lose the lozenge: zinc stinks for treating URIs
EBM Focus - Volume 15, Issue 10
Reference: BMJ Open. 2020 Jan 23;10(1)
During the cold and flu season, people look for anything to feel better. The debate over remedies for URIs has been going on probably since ancient times (i.e., the 1970s), but zinc lozenges have been both particularly well-studied and particularly contentious. Limited data suggest that zinc may shorten symptom duration.
In January, a group from Helsinki published a double-blind randomized controlled trial of zinc acetate lozenges for treatment of symptoms of upper respiratory infections (URIs).
Researchers recruited 253 employees of the city of Helsinki who self-identified as particularly susceptible to prolonged and severe URIs. About 90% of the participants were female, and most were middle-aged, exposed to children, and had to take time off from work in the preceding year for URI symptoms. In total, 88 members of this group caught URIs, including 46 in the zinc lozenge group and 42 in the placebo lozenge group. Investigators distributed lozenges to participants in advance of any potential infections and asked participants to start zinc at the first sign of infection. Participants dissolved zinc lozenges in their mouths six times per day for five days, for a total zinc acetate dose of 78 mg/day. Participants were asked about 12 different symptoms (such as hoarseness and fever) for the next 10 days, rating the severity of each symptom on a scale from one to three.
There was no difference in recovery rate between the two groups (rate ratio comparing placebo vs. zinc 0.68, 95% CI 0.42-1.08). Median duration of cold symptoms was 5 days in the placebo group and 7 days in the zinc group. Moreover, in the subgroup of patients who hadn’t improved by day 4, patients taking zinc were less likely to recover by day 7 (28% vs. 66%, p = 0.003). More patients taking zinc reported side effects than patients taking placebo (63% vs. 31%, p = 0.003), with a bad taste being the most commonly reported side effect.
The authors expected a benefit from the zinc, and the study was powered to reflect that expectation. Not only did zinc fail to show a benefit, with the point estimate favoring placebo and the confidence intervals observed, it is unlikely that a larger trial would change the outcome. The authors used a formulation and dose previously reported to be successful. Diagnosis, symptoms, and adherence were all self-reported in this study, but the authors designed a good protocol for both allocation and assessment blinding. This study provides high-quality evidence that zinc may not be helpful for treating URIs.
For more information, see the topic Upper Respiratory Infection (URI) in Adults and Adolescents in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Dan Randall, MD, Deputy Editor for Internal Medicine at DynaMed. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School, and Katharine DeGeorge, MD, MS, Associate Professor of Family Medicine at the University of Virginia and Clinical Editor at DynaMed.