Meta-analysis: Zinc really works for colds and flu

Taken together, published study data support the role of zinc supplements in the prevention and treatment of upper respiratory tract infections caused by viruses other than SARS-CoV-2 in adults.

Dr. Jennifer Hunter of Western Sydney University in Penrith, Australia, MScPH found pool data from eight randomized controlled trials of a total of approximately 3,500 people, 5 for every 100 man-months of oral or intranasal zinc treatment. It showed that two infections were prevented. And colleagues.

In addition, in approximately 1,000 people with respiratory viral 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. .. BMJ Open..

However, these obvious benefits have come with a lot of caution. The strength of the evidence, especially in the case of zinc as a treatment for ongoing infections, was low. The researchers acknowledged that the analysis was impaired by substantial bias in the studies involved, low attendance, and significant heterogeneity.

Zinc did not appear to reduce the severity of symptoms or prevent infection after a deliberate viral attack, so the benefits were not significant, they said.

In particular, whether zinc can prevent or treat COVID-19 was not included in the analysis as it contained only studies published by May 2020. SARS-CoV-2. (At least seven COVID trials of zinc were still underway when hunters and colleagues were completing the manuscript, they said.)

The researchers identified 28 randomized controlled trials with available results of zinc in the prevention or treatment of adult respiratory viral infections. The formulations used in these studies were most commonly lozenges. Others included nasal drops and gel.

Oral doses for prophylaxis ranged from 15 to 45 mg / day and were given for up to 12 months. Sublingual lozenge doses of 45-300 mg / day were used to treat active infections. Nasal doses ranged from 0.9 to 2.6 mg / day. All but three of the 28 trials were placebo-controlled. Two used quinine lozenges as controls (the author called it placebo, but hunters and colleagues considered it active), and one actively showed controls with naphazoline.

Four studies examined zinc lozenges to prevent rhinovirus infection in volunteers who agreed to receive live virus. Two of these started treatment prior to the viral challenge and two considered post-exposure prophylaxis, all using placebo controls. None of these studies showed a protective effect on zinc treatment (relative risk 0.96, 95% CI 0.77-1.21), and the strength of the evidence was considered moderate.

However, for infections acquired in the normal community, daily zinc supplements (at least for oral and intranasal preparations) seemed to help prevent. In addition to the number needed to treat (NNT) of 20 for all infectious diseases, a meta-analysis reduces the risk of developing “moderately severe symptoms” of illnesses such as influenza by 87%. We have found that the risk of mild symptoms similar to a cold is reduced by 28%. cold. The NNT for preventing moderately serious illness per 100 man-months was 100.

In the treatment of ongoing infections, a meta-analysis helped zinc reduce the severity of symptoms on the third day of clinical illness, but not on average over the entire duration of the illness. showed that. However, hunters and colleagues have shown that the quality of the underlying research is poor.

In general, the adverse effects of zinc treatment were minor and rare. They were numerically more common compared to placebo (incidence ratio 1.63) when used prophylactically, but did not reach statistical significance (95% CI 0.81-3.31). However, the high doses used to treat active infections caused gastrointestinal discomfort in some participants, and sublingual lozenges were associated with mouth inflammation. Nasal sprays and gels seemed to be more tolerable.

Meta-analysis was vulnerable to publication bias, and this was no exception. “Publication bias was not strongly suspected, but visual inspection of the Funnel plot was necessarily subjective and no statistical test of hazard ratios was performed,” the group wrote.

In addition, they acknowledged that “the number of studies and sample size were small,” and researchers were more likely to clarify the efficacy and safety of certain formulations, as well as the mechanism by which zinc fights. Has issued a standard call for research in. Virus infection.

But overall, hunters and colleagues felt that zinc was worth a try for many. “The slight benefits of other over-the-counter and prescription drugs, strain specificity, drug resistance, and potential risk make zinc a viable” natural “alternative to non-specific self-management. [respiratory tract infections], “They wrote.

They suggested that doctors could also benefit. “It also provides clinicians with management options for patients who are anxious for faster recovery times and may be seeking unnecessary antibiotic prescriptions.”