02 Nov Study Reviews Clinical Trials of Zinc In Respiratory Tract Infections
MedicalResearch.com Interview with:
Jennifer Hunter, B.Med., M.Sc.P.H., Ph.D.
Adjunct Associate Professor
NICM Health Research Institute
Western Sydney University
Associate Professor Jennifer Hunter is an academic general practitioner with a clinical interest in integrative medicine, has received payment for providing expert advice about traditional, complementary and integrative medicine, including nutraceuticals, to industry, government bodies and non-government organisations, and spoken at workshops, seminars and conferences for which registration, travel and/or accommodation has been paid for by the organisers.
MedicalResearch.com: What is the background for this study?
Response: We decided to review the evidence for zinc in response to calls for rapid evidence reviews to inform self-care and clinical practice during the COVID-19 pandemic.
Laboratory studies have found that zinc can inhibit the replication of many respiratory viruses, including SARS-CoV-2 and other coronaviruses. Zinc plays a key role in immunity, inflammation, tissue injury, ACE-2 receptor activity, and also in tissue responses to a lack of oxygen. Low zinc status may be a risk factor for severe SARS-CoV-2 illness.
Additionally, there was some indirect evidence suggesting zinc might be effective for other respiratory tract infections such as the common cold and we wanted to verify this.
MedicalResearch.com: What are the main findings?
Response: When the review was submitted for publication, the results of several relevant COVID-19 clinical trials were not available, so our review updates the available evidence about zinc’s efficacy for preventing and treating non-specific, acute viral respiratory infections.
The review included 28 clinical trials involving 5446 adults, published in 17 English and Chinese research databases up to August 2020.
When oral zinc or low dose topical nasal zinc was used for prevention, there was a 28% lower risk of symptoms consistent with the common cold and a 68% lower risk of a flu-like illness.
During the first week of illness, participants who used sublingual or topical nasal zinc were nearly twice as likely to recover as those who used placebo and it shortened the duration of symptoms by around 2 days. Zinc also reduced day 3 symptomatic severity around the peak of illness, but the reduction in overall symptom severity was insignificant.
Side effects, including nausea and mouth/nose irritation, were around 40% more likely among those using zinc, but no serious side effects were reported in the 25 trials that monitored them.
MedicalResearch.com: What should readers take away from your report?
Response: It is commonly thought that zinc’s role in preventing and treating infections is only for people who are zinc deficient; our findings really challenge this notion.
However, clinicians and consumers need to be aware that considerable uncertainty remains regarding the clinical efficacy of different zinc formulations, doses and administration routes. At the moment there just isn’t enough research to say whether a zinc nasal spray, versus a nasal gel, versus a lozenge, versus oral zinc is any better or worse than the others. Most of the trials used zinc gluconate or zinc acetate formulations, but that doesn’t mean that other zinc compounds are less effective.
Also, the use of zinc is not 100% risk free. There are post market reports of permanent loss of smell from a zinc nasal gel and the long term use of higher doses of sublingual or oral zinc can cause copper deficiency.
Despite these uncertainties, zinc products are widely available, affordable, and generally safe, including the short-term use of high dose zinc lozenges and capsules that was used in many of the trials. This provides clinicians and patients with a viable alternative to the inappropriate use of antibiotics, that continues to be a major problem globally.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: The comparative effectiveness of various zinc doses, formulations and administration routes needs to be evaluated.
SARS-CoV-2 clinical trials should consider replicating the zinc interventions and study designs of clinical trials with positive results for other viral respiratory tract infections.
The effects of zinc in supporting recovery, for example, from anosmia (loss of smell) and long-covid should also be investigated.
MedicalResearch.com: Is there anything else you would like to add?
Response: This study was unfunded. Study investigators volunteered their services and have no direct conflicts of interest to declare.
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 2021;11:e047474. doi: 10.1136/bmjopen-2020-047474
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