Every cold and flu season, folks are flooded with ads for zinc lozenges, sprays and syrups that promise to shorten their sniffles.

Zinc might indeed reduce the duration of common cold symptoms by about two days, a new evidence review says.

However, the evidence is not conclusive, and taking zinc can come with some unpleasant side effects, researchers said.

“The evidence on zinc is far from settled,” senior researcher Susan Wieland, an assistant professor at the University of Maryland School of Medicine, said in a news release. “We need more research before we can be confident in its effects.”

The theory behind zinc is that the essential mineral, which is found in many foods, might interfere with the cold virus’ ability to replicate in the nose, mouth and throat, researchers said.

Lab studies have shown zinc can do this in petri dishes and mice, but human studies are needed to show if it will work in real people.

For this review, researchers evaluated 19 human trials examining zinc as a cold treatment and 15 as a means of preventing colds.

In particular, eight studies with nearly 1,000 participants combined investigated zinc as a treatment to reduce cold duration.

The pooled results of those studies showed that it might help reduce the length of a cold by about two days, down from an average week-long duration in people who received a placebo.

However, the overall evidence did not support zinc’s ability to ward off a cold or to reduce the severity of cold symptoms.

The research team also noted that taking zinc comes with side effects like bowel problems, nausea and unpleasant taste.

“People considering zinc to treat a cold should be aware of the limited evidence base and possible side-effects,” lead researcher Daryl Nault, an assistant professor at Maryland University of Integrative Health, said in a news release. “Ultimately, it’s up to the individual to decide whether the risk of potential unpleasant side-effects is worth the benefit of potentially shortening their illness by a few days.”

Nault said the best advice remains to call your doctor if you don’t feel well and let them know if you use any supplements.

“While there have been many trials investigating zinc, the approaches vary, so it is difficult to draw conclusions with certainty,” she added.

Part of the problem with this evidence review is that zinc doses and delivery methods varied widely between studies, as well as how people’s health was reported and measured, researchers said.

“Future studies should adopt standardized methods for administering and reporting treatments and defining and reporting outcomes,” Wieland said. “Additional studies focusing on the most promising types and doses of zinc products and using appropriate statistical methods to assess outcomes that are important to patients will enable us to understand whether zinc may have a place in treatment of the common cold.”

The new study appears in the Cochrane Database of Systematic Reviews.

More information

The University of Southern California has more on zinc for cold relief.

SOURCE: Cochrane, news release, May 8, 2024