Zinc supplement may help ward off symptoms of respiratory infections, such as coughing, congestion, and sore throat and reduce the duration of illness, suggests a pooled analysis of the available evidence, published in the Open Access Journal. BMJ is open.
But the quality of the evidence on which these findings are based is variable, and it is not clear what the optimal formula or dose of this nutrient is, the researchers cautioned.
Respiratory infections include colds, flu, sinusitis, pneumonia, and COVID-19. Most infections go away on their own, but not all. They are often costly in terms of their impact on health services and time spent on sick leave.
Zinc plays a key role in immunity, inflammation, tissue injury, blood pressure, and tissue responses to hypoxia.
As a result, it has generated great interest during the current pandemic for the prevention and treatment of COVID-19 infection.
In response to calls for rapid assessments of evidence to guide self-care and clinical practice, researchers have evaluated zinc for prevention and treatment of SARS-CoV-2, the virus responsible for COVID-19, and other viral respiratory infections.
When this review was published, the results of several relevant clinical trials were not yet available, so this current review brings the available evidence up-to-date.
The review includes 28 clinical trials, including 5,446 adults, published in 17 research databases in English and Chinese as of August 2020. None of the trials specifically addressed the use of zinc to prevent or treat COVID-19.
The most common zinc formulations were lozenges followed by nasal sprays and gels containing either zinc acetate or gluconate salts. Dosages vary widely, depending on the formulation and whether zinc is used for prevention or treatment.
A pooled analysis of the results of 25 trials showed that compared to placebo (a dummy treatment), zinc lozenges or nasal spray prevented 5 respiratory infections in 100 people per month.
These effects were stronger in reducing the risk of more severe symptoms, such as fever and flu-like illnesses. But this is based on only three studies.
On average, symptoms disappeared 2 days earlier with either a zinc spray or a liquid formulation taken under the tongue (under the tongue) than with a placebo.
During the first week of illness, participants who used zinc under the tongue or nasal spray were nearly twice as likely to recover as those who used the placebo: symptoms were likely to persist a week after 19 adults out of 100 took if they did not use zinc supplements.
While zinc was not associated with a reduction in average daily symptom severity, it was associated with a clinically significant reduction in day three symptom severity.
Side effects, including nausea and mouth/nose irritation, were 40% more likely among those using zinc, but no serious side effects were reported in the 25 trials that monitored them.
However, compared to placebo, sublingual zinc did not reduce the risk of developing infection or symptoms of the common cold after vaccination with human rhinovirus, and there were no differences in disease duration between those who used zinc supplements and those who did not.
The relative efficacy of different zinc formulations and doses was not clear. The quality, size and design of the included studies varied widely.
Marginal benefits, strain specificity, drug resistance, and potential risks of other over-the-counter and prescription drugs make zinc a viable ‘natural’ alternative for self-administration of non-specific drugs. [respiratory tract infections]The researchers write.
“[Zinc] It also provides clinicians with a management option for patients who desperately need to recover faster and may seek an unnecessary prescription of antibiotics.”
“However, clinicians and consumers should be aware that there remains a great deal of uncertainty regarding the clinical efficacy of different formulations, doses, and routes of administration of zinc, and the extent to which efficacy is affected by the ever-changing epidemiology of viruses that cause [respiratory tract infections],” they warn.
They conclude that the manner in which zinc may exert its therapeutic effects on respiratory infections, including COVID-19, requires further research.
Hunter, c. et al. (2021) Zinc for prevention or treatment of acute respiratory viral infections in adults: a rapid systematic review and meta-analysis of randomized controlled trials. BMJ is open. doi.org/10.1136/bmjopen-2020-047474.