Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Many of us experience the nuisance of having a common cold, and a variety of interventions have been suggested to prevent or treat it. One of these is zinc and a new Cochrane Review, published in May 2024, looks at the evidence. Here's the first author, Daryl Nault from Maryland University of Integrative Health in the USA to tell us what the review found.

Daryl: The common cold is a contagious viral infection of the upper respiratory tract, with symptoms such as runny or stuffy nose, sneezing, sore throat, cough, body aches, and fatigue. Although the immune system can usually clear the infection within a week or two, many people turn to over-the-counter zinc supplements hoping to prevent or treat cold symptoms. Our review aimed to assess whether zinc can prevent the common cold or affect its duration, severity, and other potential impacts. We also wanted to look at safety.
We identified 34 studies with a total of just over 8,500 participants that compared zinc with a placebo in both adults and children. The studies covered a broad geographic range, with representation from Asia, Europe, Africa, South America, and Australia, but most studies took place in the USA. Nineteen studies related to treatment, with eight others looking at prevention of the common cold and seven targeting the prevention of upper respiratory tract infections more generally.
Lozenges were the most commonly tested form of zinc, with zinc gluconate being the most frequently used type of zinc, in contrast to zinc orotate or acetate.  Dosage and treatment duration also varied considerably across the studies. For example, the doses for zinc gluconate lozenges ranged from 45 to 276 mg/day, over 4.5 to 21 days. Other delivery methods included capsules, dissolved powders, tablets, syrups, and intranasal administration.
Due to the wide variation in methodologies and the fact that so many studies had unclear or high risk of bias, it's difficult to draw any conclusions with certainty. However, with that in mind, the current evidence suggests that taking zinc preventatively may have little to no effect on the duration, severity, or risk of catching a cold. Results were only slightly more promising for zinc as a treatment for the cold, where findings suggest that zinc might shorten the duration of symptoms by about two days compared to a placebo.
In both prevention and treatment studies, side effects such as altered taste and stomach upset were more common with zinc lozenges than with placebo. This makes it important to note that side effects might outweigh any potential benefits for some people. And, given our review's findings, further research with more consistent methodologies is needed before suggesting any changes be made to current clinical practice.
As my take home message, if you're considering using zinc or any over-the-counter supplement for the common cold, it's important to talk to your clinician. They can help you to weigh the potential benefits and harms based on your individual health needs.

Mike: If you would like to learn more about the findings of Daryl's review and the types of zinc supplement that have been tested, it's available online. If you go to Cochrane Library dot com and search 'zinc and the common cold' you'll see a link to it.