Can zinc shorten the length of a common cold?

Taking zinc for a runny nose may reduce cold symptoms by a couple of days, but it's not guaranteed, a new systematic review of existing research finds.

The review included more than 30 studies that looked at people taking zinc as a cold preventative or as a treatment for symptoms colds.

In breaking down these studies, the review authors said they found no evidence that zinc is beneficial for cold prevention, but a review of eight studies involving nearly 1,000 participants on zinc use as a treatment for cold symptoms showed "low confidence evidence" that this element could shorten the duration of a cold by a couple of days.

Zinc and colds

The theory behind using zinc to treat colds is that it can interrupt the replication of the cold virus, similar to the action of an antiviral drug.

However, although zinc is widely promoted in a variety of forms with claims to help treat or prevent colds—from tablets to sprays, syrups and lozenges—there is no consensus regarding its effectiveness or which form is better than another.

“The timing of zinc supplementation in relation to the onset of cold symptoms may influence its effectiveness, adding complexity to study design,” said Dr. Monica Amin, PharmD, a pharmacist with Marley Drug and Medicure pharmaceutical companies who was not involved in the study.

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“Differences in immune responses and genetic factors among individuals may influence their response to treatment, contributing to variability in study results,” Amin told Medical News Today. "These factors combine to contribute to the difficulty of determining whether zinc is an effective treatment for the common cold."

However, experts say this review should help point the way to better future research on zinc to definitively determine its effectiveness.

“The evidence on zinc is far from conclusive: we need more research before we can be confident about its effects,” said Dr. Susan Wieland of the University of Maryland School of Medicine and senior author of the review, in a press release. “Future studies should adopt standardized methods for administering and reporting treatment, as well as defining and reporting outcomes. Additional research focusing on the most promising types and dosages of zinc products and using appropriate statistical methods to evaluate outcomes important to patients will allow us to understand whether zinc has a place in the treatment of colds."

Then there is the question of even how to define a “cold” in the context of a clinical trial.

“There is no uniformity in determining who has a cold. And even people who have classic cold symptoms with fever, runny nose and sore throat can be infected with one of many viruses: adenovirus, rhinovirus, metapneumovirus, influenza, RSV or even COVID,” said Dr. David Cutler, a family medicine physician. At Providence Saint John's Medical Center in California, who was not involved in the study.

“So without knowing what we are treating and including patients with different diseases, it is difficult to conclude that a particular treatment improves a particular disease,” Cutler said.

Should I take zinc for a cold?

So, the decision about whether to take a supplement with a nutrient that may (or may not) help fight a cold ultimately depends on the individual, but experts say there are some factors that should be considered. Take into account, including side effects.

"It's possible that zinc can sometimes improve a viral cold, but its potential benefits must be weighed against its potential risks," Cutler said. “Zinc can irritate the stomach, causing nausea, abdominal pain and sometimes vomiting. The chemical similarities between zinc and copper can cause zinc to block the absorption of copper, leading to copper deficiency. Copper deficiency may manifest as neuropathy, anemia, or impaired immune function."

Additionally, the Federal Food and Drug Administration has also warned against the use of zinc nasal sprays due to the risk of decreased or loss of sense of smell.

“If a patient can start taking zinc at the onset of cold symptoms without developing stomach upset, it will probably be safe for them,” Amin said. “To ensure safety, patients should consult with their healthcare provider before starting any new supplement program as supplements may potentially cause side effects and interact with medications.”