Taking a zinc supplement could fend off the symptoms of respiratory tract infections and reduce the time of illness, new analysis reveals today.
However, the authors, who studied the latest available evidence urge caution about their findings, saying the quality of evidence is variable.
Writing in BMJ Open, they also say it is not clear what the best formulation or dose would be.
Because of zinc’s role in immunity, inflammation, tissue injury, blood pressure and in tissue responses to lack of oxygen, it was considered as a possible prevention and treatment for COVID-19.
This up-to-date review includes 28 clinical trials, published in 17 English and Chinese research databases up to August 2020. None of the trials specifically examined the efficacy of zinc for the prevention or treatment of COVID-19.
The studies used different formulations, most commonly lozenges, nasal sprays and gels containing either zinc acetate or gluconate salts, and doses also varied considerably, depending on the formulation and if zinc was being used for prevention or treatment.
The pooled results of 25 trials showed that compared with placebo, zinc lozenges or nasal spray prevented five respiratory tract infections in 100 people a month, while three studies showed the effects were best for reducing the risk of developing more severe symptoms, such as fever and influenza-like illnesses.
On average, using a zinc spray or sublingual liquid formulation saw symptoms clear up two days earlier compared with placebo.
Participants who used sublingual or nasal spray zinc were nearly twice as likely to recover as those who used placebo, with 19 more adults out of 100 being likely to have symptoms a week later if they did not use zinc supplements.
The authors also found that while zinc was not associated with an easing in average daily symptom severity, it was associated with a clinically significant reduction in symptom severity on day three.
Sublingual zinc was not found to reduce the risk of developing an infection or cold symptoms after participants were inoculated with human rhinovirus and no differences were found in the length of illness between those who used zinc supplements and those who did not.
The authors, who included researchers from Western Sydney University, Australia; National University of Natural Medicine, Portland, Oregon, USA; and Southern Cross University, Lismore, New South Wales, Australia; said: “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 RTIs.
“It also provides clinicians with a management option for patients who are desperate for faster recovery times and might be seeking an unnecessary antibiotic prescription.
“However, clinicians and consumers need to be aware that considerable uncertainty remains regarding the clinical efficacy of different zinc formulations, doses and administration routes, and the extent to which efficacy might be influenced by the ever changing epidemiology of the viruses that cause RTIs.”
Hunter J, Arentz S, Goldenberg J et al. Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials. BMJ Open 2 November 2021; doi 10.1136/bmjopen-2020-047474
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