Zinc could prevent and relieve respiratory tract infections, but questions remain: study

A woman is seen lying in bed while blowing her nose. (Pexels)

Toronto -

A new study has found that zinc might be able to prevent and relieve symptoms of respiratory tract infections, such as the flu and pneumonia.

However, researchers warn that the optimal dosage, formulation and administration method remain unclear.

"In response to calls for rapid evidence appraisals to inform self-care and clinical practice during the COVID-19 pandemic, we developed a rapid systematic review protocol to evaluate zinc for the prevention and treatment of SARS-CoV-2 and other viral (respiratory tract infections)"

The peer-reviewed study -- published on Monday in BMJ Open -- involved researchers from Australia, the United States and McMaster University in Hamilton. The researchers conducted a meta-analysis examining the results of 28 placebo-controlled randomized trials involving 5,446 participants.

Treatment options for those with respiratory infections are limited, but zinc products have been a surge in interest amid the COVID-19 pandemic due to its immune system-strengthening properties.

"Not surprisingly, zinc has garnered attention during the global COVID-19 pandemic. Both high-income and low-income countries have seen increased zinc supplement use and sales," the authors wrote.

Compared against a placebo, the trials showed that zinc supplements prevented five respiratory tract infections in 100 people per month.

In addition to prevention, zinc was found to be associated with faster recovery. On average, symptoms of respiratory tract infections resolved two days earlier compared to the placebo. Zinc was also associated with "significant reductions" in symptom severity on the third day of illness.

Participants who used zinc products during the first week of illness were also nearly twice as likely to recover compared to those who used a placebo. On average, 19 per cent of those who did not use zinc remained symptomatic after a week.

"The marginal benefits, strain specificity, drug resistance and potential risks of other over-the-counter and prescription medications makes zinc a viable 'natural' alternative for the self-management of non-specific (respiratory tract infections)," the authors wrote.

The treatments were also associated with a few side effects. Nausea, as well as irritation in the mouth and nose were around 40 per cent more likely among those who used zinc, but none of the trials reported any serious side effects.

However, zinc was found to be ineffective when it came to colds, which are caused by rhinovirus infections. The researchers found that sublingual zinc, which is administered under the tongue, had no effect on preventing colds or easing symptoms.

The researchers caution that there remains "considerable uncertainty" regarding the efficacy of different dosages, formulations and administration routes. In addition to sublingually, zinc can be administered through lozenges, nasal sprays and gel capsules.

The authors note that there was no consistency between the trials in the dosage or the formulation of the zinc supplements and none of the studies compared the effectiveness of dosages or formulations. In addition, none of the trials specifically looked at COVID-19 patients.

"Clarification of the efficacy and mechanism of zinc in viral respiratory infections, including SARS-CoV-2 infections, warrants further research," the authors wrote.