Zinc is often suggested for a lost sense of smell. Pooling six studies and 1,460 people, Brazilian researchers found no clear benefit

Losing the sense of smell is more common than many people think, and since the COVID-19 pandemic far more people have lived with it. Zinc gets suggested a lot as a fix: the mineral helps the lining of the nose renew itself, and low zinc has been linked with a poorer sense of smell. A team from the State University of Londrina and the University of São Paulo set out to see whether taking it actually helps. Their systematic review and meta-analysis was published online by the Brazilian Journal of Otorhinolaryngology on 28 October.

The search ran through PubMed, the Cochrane Library, Scopus and Web of Science up to April 2025 and turned up 731 records. Only six studies compared people given zinc with people who were not: three randomised controlled trials and three observational cohorts, published between 1976 and 2024. Together they covered 1,460 people, 436 of them on zinc, whose smell loss followed infections, head injuries, chemotherapy or had no known cause. The products differed widely, from zinc oxide and zinc gluconate to zinc sulphate, at 17 mg to 300 mg a day for one to fifteen months.

On objective smell tests, such as the University of Pennsylvania Smell Identification Test, the pooled odds ratio for improvement was 1.78, but the confidence interval ran from 0.63 to 5.03, so the result was not statistically significant (p = 0.28). People's own sense of whether their smell had come back pointed the other way, at an odds ratio of 0.69 (0.25 to 1.93, p = 0.48). Only one study, on parosmia and phantosmia (smells that are distorted or not there at all), looked at those symptoms, and it also found no clear effect.

The exception was a 2015 trial of 145 people who had lost their sense of smell after a head injury. Those given 30 mg of zinc gluconate a day were almost five times as likely to improve (odds ratio 4.9). The authors say that targeted groups like this deserve proper trials, but on current evidence zinc should not be routinely recommended. The review has clear limits: only six studies, results that varied a lot between them (I² of 63% and 91%), half the studies observational, and side effects described in only one trial, the 1976 one, where they were mild stomach complaints such as cramps and diarrhoea.