Zinc May Shorten the Common Cold, But Not Prevent It: Cochrane Review

Zinc is widely known to modulate the immune system, but some researchers say they have ‘little confidence’ that zinc can reduce the duration of a cold.

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Supplementing with zinc may not prevent the common cold, but evidence suggests it could reduce its duration by several days, according to a systematic review.

A paper recently published in the Cochrane Database of Systematic Reviews examined 34 existing studies involving 8,526 participants to evaluate whether zinc is effective and safe in preventing and treating the common cold. Nineteen of the human trials looked at zinc as a treatment, and 15 assessed its ability to prevent a cold.

When researchers broke down the studies, they found there may be little or no reduction in the risk of developing a cold when supplementing with zinc compared to placebos. However, a review of eight studies of 972 people found that taking zinc may reduce the length of cold symptoms by about two days.

At the same time, the researchers said they had little confidence in the evidence showing zinc could positively impact the severity of cold symptoms.

“The evidence on zinc is far from settled: we need more research before we can be confident in its effects,” said senior author Susan Wieland, an assistant professor at the University of Maryland School of Medicine in a Cochrane news release. “Future studies should adopt standardized methods for administering and reporting treatments and defining and reporting outcomes. 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 the treatment of the common cold.”

As for adverse events, common side effects potentially due to zinc supplementation reported during the trials included unpleasant taste, loss of smell, vomiting, stomach cramps, and diarrhea. No serious adverse events were reported. Still, researchers said the potential benefits of taking zinc should be balanced against side effects.

“People considering zinc to treat a cold should be aware of the limited evidence base and possible side-effects,” co-author Daryl Nault of Maryland University of Integrative Health said in the 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.”

What Is Zinc?

According to the National Institutes of Health, zinc is an essential mineral involved in many biological processes, including immune function, wound healing, DNA synthesis, and cell division. It also affects a person’s ability to taste and smell.

Numerous studies show that zinc deficiency can impair immune function and increase the risk of infections. Zinc can also impair antibody production and alter the expression of cytokines—which help coordinate the body’s immune response—and can weaken the immune system’s ability to mount an effective response against pathogens. 

“Zinc is known to act as an immune modulator, which plays an important role in the immune defense system,” Dr. Craig M. Wax, a physician and health care policy expert, told The Epoch Times. 

Zinc has been widely considered as an anti-inflammatory and an antioxidant agent, and, when used with other compounds, shortens the duration of illness and reduces its severity. For example, all of the agents we used against COVID-19 in the field, such as hydroxychloroquine and quercetin, brought zinc into the cell to perform the actions, Dr. Wax said. 

Moreover, zinc “lowers the severity of ssRNA [single-stranded RNA] infections and shortens the duration of infection when taken early.” Zinc also “plays an inhibitory role in almost the entire life cycle of HSV [herpex simplex virus],” he added. 

In a previous Cochrane review on zinc, researchers examined 15 randomized, double-blind, placebo-controlled trials using zinc lozenges for at least five consecutive days to treat, or for at least five months to prevent the common cold. They found that zinc supplementation was associated with a “significant reduction” in cold duration and severity and found a “significant difference” between people who took zinc and the control groups.

Notably, zinc taken within 24 hours of symptom onset reduced the duration and severity of cold symptoms in healthy people. When zinc was taken for at least five months for prevention, researchers found that the incidence of colds, school absences, and prescriptions for antibiotics decreased for children.

Trial Differences May Explain Review Findings

Although the recent Cochrane review included 34 trials, they varied in many ways. The trials used different types and dosages of zinc and various methods of administration. Seventeen of the 34 studies used zinc lozenges. Some studies used zinc acetate, while others used zinc gluconate and orotate. The dosages varied from 45 to 276 milligrams per day. One study administered zinc gluconate intranasally and in conjunction with oral zinc orotate. 

Of the 17 studies that did not use lozenges, zinc was administered in capsules, dissolved powders, tablets, syrups, and intranasally. The trials did not include the variations of zinc that are known to be most bioavailable, such as zinc picolinate and zinc bisglycinate, nor did they include zinc citrate, zinc glycinate, or zinc monomethionine.

Additionally, there was no consistency in how the outcomes were measured or reported. Some trials used a fixed time window and asked participants if they still had a cold at the end. Others measured the time between symptoms starting and resolving, and each study defined this slightly differently. Most of the studies did not monitor individual symptoms, such as sore throat, cough, or fever, so there was “insufficient evidence to draw any reliable conclusions about specific symptoms,” according to the Cochrane news release. The methods used to test whether zinc was effective also varied significantly.

Finally, some studies did not adequately report how people were randomly placed into treatment groups, which could account for the differences observed between study groups.