Meta-analysis: zinc is really effective against colds and flu

Overall, published trial data support the role of zinc supplements in preventing and treating upper respiratory tract infections caused by viruses other than SARS-CoV-2 in adults, a meta revealed. -to analyse.

Pooled data from eight randomized controlled trials involving a total of some 3,500 people indicated that five infections were prevented per 100 person-months of oral or intranasal zinc treatment, reported Jennifer Hunter, PhD, MScPH, of the Western Sydney University in Penrith, Australia, and colleagues.

In addition, in about 1,000 people who contracted viral respiratory infections, treatment with sublingual or intranasal zinc preparations reduced the duration of symptoms by an average of 2 days compared to placebo, the group reported in BMJ Open.

But with these apparent benefits came many caveats: the strength of the evidence (especially for zinc as a treatment for an ongoing infection) was low. The analysis was marred by substantial bias in the included studies, a small number of participants and significant heterogeneity, the researchers conceded.

And the benefits were modest, they noted, as zinc did not appear to reduce the severity of symptoms or prevent infection after deliberate viral challenge.

Notably, the analysis did not address the question of whether zinc could prevent or treat COVID-19, as it only included studies published up to May 2020 – at this point it would have been too early. to design, conduct and publish a randomized trial for SARS-CoV-2. (At least seven COVID zinc trials were still ongoing when Hunter and his colleagues were finalizing their manuscript, they noted.)

Researchers identified 28 randomized controlled trials with results available for zinc in the prevention or treatment of respiratory viral infections in adults. The formulations used in these studies were most often lozenges; others included nasal sprays and gels.

Oral doses for prevention ranged from 15 to 45 mg / day, given for up to 12 months. In the treatment of active infections, doses of sublingual lozenges of 45 to 300 mg / day have been used; nasal doses ranged from 0.9 to 2.6 mg / day. All but three of the 28 trials were placebo-controlled; two used a quinine lozenge as a control (their authors called it placebo, but Hunter and colleagues found it to be active), and one was actively controlled with naphazoline.

Four studies looked at zinc lozenges to prevent rhinovirus infection in volunteers who agreed to be inoculated with a live virus. Two of them started treatment before viral challenge and two looked at post-exposure prophylaxis, and all used placebo control. None of these studies showed a preventive effect for zinc treatment (relative risk 0.96, 95% CI 0.77-1.21), and the strength of the evidence was considered moderate.

But for infections acquired in ordinary community settings, daily zinc supplements (at least for oral and intranasal formulations) appeared to help prevention. In addition to the number needed to treat (NNT) of 20 for all infections, the meta-analysis found an 87% reduced risk of developing ‘moderately severe symptoms’ of ILI, as well as a 28% lower risk of mild symptoms. resembling common symptoms. colds. The NST for the prevention of moderately severe disease per 100 person-months was 100.

In the treatment of the current infection, the meta-analysis showed that zinc helped reduce the severity of symptoms on day 3 of clinical disease, but not when averaged over the course of the disease. Hunter and his colleagues, however, indicated that the quality of the underlying studies was low.

In general, adverse reactions attributed to zinc treatment were minor and infrequent; they were numerically more frequent compared to placebo (incidence rate ratio 1.63) when used for prophylaxis, but not to the point of statistical significance (95% CI 0.81-3.31) . However, the higher doses used for the treatment of active infection resulted in gastrointestinal discomfort in some participants, and sublingual lozenges have been associated with mouth irritation. Nasal sprays and gels seemed to be better tolerated.

Any meta-analysis is vulnerable to publication bias, and this one is no exception. “Although publication bias was not strongly suspected, visual inspection of funnel charts is necessarily subjective and statistical testing of risk ratios has not been performed,” the group wrote.

Further, they recognized that “the number of studies and sample sizes were small,” and the researchers made the standard call for more research – not only for the efficacy and safety of particular formulations, but also to clarify the mechanisms by which zinc can fight viral infections.

But, overall, Hunter and his colleagues felt that zinc would be worth a try for many people. “The marginal benefits, strain specificity, drug resistance, and the potential risks of other over-the-counter and prescription drugs make zinc a viable ‘natural’ alternative for self-management of non-specific illnesses. [respiratory tract infections],” they wrote.

Doctors could also benefit, they suggested: “It also gives clinicians a management option for patients who are desperate for faster recovery times and might be looking for a prescription for unnecessary antibiotics.”