Zinc and colds; A new study published in BMJ Open adds to the evidence that zinc is effective against viral respiratory infections, such as colds.
Researchers separately looked at whether zinc prevented or treated respiratory tract infections
Jennifer Hunter, PhD, BMed, of the NICM Health Research Institute, Western Sydney University, New South Wales, Australia, and her colleagues conducted a meta-analysis of 28 randomized controlled trials (RCTs). They searched 17 databases in English and Chinese to identify trials and then used the Cochrane rapid review technique for analysis.
The trials included 5446 adults who had received zinc in a variety of formulations and routes: oral, sublingual, and nasal spray. The researchers separately analyzed whether zinc prevented or treated respiratory tract infections (RTIs)
Zinc and colds RESULTS:
Zinc use was also associated with an 87% lower risk of developing moderately severe symptoms (incidence rate, 0.13; 95% CI, 0.04 – 0.38) and a 28% lower risk of developing. milder symptoms. The largest reductions in RR were for moderately severe symptoms consistent with influenza-like illness.
Symptoms resolved two days earlier with sublingual or intranasal zinc compared to placebo (95% CI 0.61 to 3.50, very low-certainty quality of evidence).
There were clinically significant reductions in symptom severity scores on day 3 (mean difference, -1.20 points, 95% CI, -0.66 to -1.74, low-certainty quality evidence) but no in the general severity of symptoms. Participants who used topical or sublingual nasal zinc early in their illness were 1.8 times more likely to recover than those who used a placebo.
They found no benefit from zinc when patients were inoculated with rhinovirus
However, the researchers found no benefit from zinc when the patients were inoculated with rhinovirus; there was no reduction in the risk of developing a cold. When asked about this disparity, Hunter said:
“It could well be that by inoculating people to make sure they get infected, it gives them a really high dose of the virus. [Esto] it doesn’t really mimic what happens in the real world. ” “
On the downside of supplemental zinc, there were more side effects among those using zinc, including nausea or gastrointestinal upset, mouth irritation, or pain from sublingual lozenges (RR, 1.41; 95% CI, 1.17 – 1.69; number needed to harm 7; moderate-certainty quality evidence).
The risk of a serious adverse event, such as loss of smell or copper deficiency, was low. Although not found in these studies, post-marketing studies have found that there is a risk of severe and in some cases permanent loss of smell associated with the use of nasal gels or sprays containing zinc. Three of these products were recalled.
The trial was unable to provide answers on the comparative efficacy of different types of zinc formulations, nor were the researchers able to recommend specific dosages. The trial was not designed to evaluate zinc for the prevention or treatment of COVID-19.
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