BMJ study on Zinc for Colds and Flu

A new study, published in BMJ Open in November 2021, evaluated the use of zinc for the prevention or treatment of acute viral respiratory tract infections (RTIs) in adults. The analysis of randomized controlled trials involved 17 English and Chinese databases, reviewing more than 1,300 previous studies and analyzing 28 trials.  Over 5400 participants were identified.  

As a treatment for colds and flu, zinc reduced symptoms by two days, compared to placebo. The study estimated that of 100 people with upper respiratory infections, an additional 19 people recovered by day seven due to zinc treatment.  Symptom severity appeared to be lower for those treated with zinc—with improvements seen by day three—compared to placebo. Those taking zinc had a significantly lower risk—87%—of developing severe symptoms.  

In terms of prevention of colds and flu-like illness, oral zinc supplements and nasal spray were found to have a modest effect compared to placebo, with one out of 20 infections prevented. Preventive effects were most significant in reducing severe symptoms.  

Overall, researchers concluded that in adult populations unlikely to be zinc deficient, there was evidence suggesting zinc might prevent RTI symptoms and shorten its duration.  Some people, however, may not be able to tolerate zinc due to non-serious adverse effects such as nausea and nasal irritation. Researchers were unable to clearly ascertain the efficacy of different dosages and delivery (oral or nasal spray).

The quality of the evidence was deemed by the authors to be limited due to small sample sizes, heterogeneity, and risk of bias. Further research, including clinical trials for zinc efficacy for COVID-19 prevention and treatment, is warranted, they concluded.