Zinc Supplements May Help To Stave Off Respiratory Infections Such As Colds, Flu, and COVID-19

But quality of evidence variable, and no clarity on optimal formulation or dose.

A zinc supplement may help prevent the symptoms of respiratory infections, such as coughing, congestion and sore throat, and shorten illness duration, suggests a pooled analysis of the available evidence, published in the open access journal BMJ Open.

But the quality of evidence on which these findings are based is variable, and it’s not clear what an optimal formulation or dose of this nutrient might be, the researchers warn.

Respiratory infections include the common cold, flu, sinusitis, pneumonia, and COVID-19. Most infections go away on their own, but not all. And they often prove costly in terms of their impact on health services and the time it takes for sick leave.

Zinc plays a key role in immunity, inflammation, tissue damage, blood pressure and in tissue responses to oxygen deprivation.

As a result, it has generated a lot of interest in the possible prevention and treatment of COVID-19 infection during the current pandemic.

In response to calls for rapid reviews of evidence to inform self-care and clinical practice, the researchers evaluated zinc for the prevention and treatment of SARS-CoV-2, the virus responsible for COVID-19 and other viral respiratory infections.

When that review was published, the results of several relevant clinical studies were not yet available, so this current review updates the available evidence.

The review includes 28 clinical studies involving 5446 adults, published in 17 English and Chinese research databases as of August 2020. None of the studies looked specifically at the use of zinc for the prevention or treatment of COVID-19.

The most commonly used zinc formulations were lozenges followed by nasal sprays and gels containing either zinc acetate or gluconate salts. Doses varied significantly depending on the formulation and whether zinc was used for prevention or treatment.

Pooled analysis of the results of 25 studies showed that compared to sham treatment (placebo), zinc tablets or nasal spray, 5 respiratory infections occurred in 100 people per month.

These effects were strongest for reducing the risk of developing more serious symptoms, such as fever and flu-like illness. But this is based on only three studies.

On average, symptoms resolved 2 days earlier when using a zinc spray or liquid formulation under the tongue (sublingually) than when using a placebo.

During the first week of illness, participants who used zinc sublingually or nasal spray were almost twice as likely to recover as those who took placebo: 19 more out of 100 adults probably still had symptoms a week later if they didn’t take zinc supplements.

While zinc was not associated with a reduction in mean daily symptom severity, it was associated with a clinically significant reduction in symptom severity on Day 3.

Side effects, including nausea and mouth/nose irritation, were about 40% more common in those taking zinc, but no serious side effects were reported in the 25 studies that monitored them.

However, compared to placebo, sublingual zinc did not reduce the risk of developing infection or cold symptoms after human rhinovirus inoculation, nor were there any differences in disease duration between those who took zinc supplements and those who did not.

Nor was the comparative effectiveness of different zinc formulations and doses apparent. And the quality, size and design of the included studies varied considerably.

“The marginal benefits, species specificity, drug resistance and potential risks of other over-the-counter and prescription drugs make zinc a viable ‘natural’ alternative for the self-management of non-specific [respiratory tract infections], the researchers write.

“[Zinc] also provides clinicians with a management option for patients desperate for faster recovery times and potentially seeking an unnecessary prescription for antibiotics,” they added.

“However, clinicians and consumers should be aware that significant uncertainty remains about the clinical efficacy of various zinc formulations, doses and routes of administration, and the extent to which efficacy may be affected by the ever-changing epidemiology of the viruses that [respiratory tract infections]”, they warn.

And exactly how zinc might exert its therapeutic effects on respiratory infections, including COVID-19, warrants further research, they conclude.

Reference: “Zinc for the prevention or treatment of acute viral respiratory infections in adults: a rapid systematic review and meta-analysis of randomized controlled trials” Nov 1, 2021, BMJ Open.
DOI: 10.1136/bmjopen-2020-047474