Zinc and the Common Cold: What Science Really Says

Does zinc really work for cold? For several years, zinc lozenges, zinc tablets, and zinc nasal sprays have been widely advertised as a cold remedy. Parents purchase them in large quantities in the season of cold and flu. Fitness buffs have extolled their virtues. However, doctors have been politely noncommittal.

It’s complicated. The medical community has had more arguments about this topic than most people can even begin to imagine. But two major reviews were published in 2024, and they’ve given us the best information that’s currently available, and the results are more complicated, and more interesting, than a simple yes or no answer.

What Is Zinc?

Zinc constitutes an essential mineral, which your body requires to conduct more than 300 different biological operations, including wound healing, infection defense, protein production and functioning of taste buds and smell. You can obtain zinc through your diet from meat, shellfish, beans, seeds and dairy products.

Scientists first discovered that zinc prevents colds through their research work during the early 1980s. A three-year-old girl with leukemia had a cold. She preferred to let the zinc medicine dissolve in her mouth instead of taking it orally. Her cold symptoms disappeared within a few hours. Her father who worked as a researcher, investigated this and conducted his own clinical trial, which showed that zinc gluconate lozenges could effectively reduce cold symptoms for an extended period.

This accidental discovery has led to decades of research, controversy, and mixed findings. The question that researchers have been attempting to answer ever since: Does zinc really work, and if so, how, when, and for whom?

Research on Zinc

In May 2024, the Cochrane Database published its first major review of zinc, the most comprehensive analysis of zinc research up to that time.

The studies investigated two different aspects of common cold. First was prevention methods and second was related to treatment methods, which used various zinc delivery systems including oral tablets, lozenges, syrups and nasal spray.

The researchers reached a tentative conclusion because their review showed that current evidence did not support any definite findings about zinc supplementation for cold prevention or treatment.

That looks like a definite no. But it’s a bit more complicated when you look at the specifics.

Only a short while later, in September 2024, two leading zinc researchers, Harri Hemila of the University of Helsinki and Elizabeth Chalker of the University of Sydney, published a critique of the Cochrane review in the peer-reviewed medical journal Frontiers in Medicine.

They claimed that the Cochrane review contained serious errors in methodology that resulted in an unduly negative conclusion.

In particular, they noted that the review included wildly disparate forms of zinc administration together in the same analysis, including trials using nasal sprays containing just 0.046 mg of Zinc per day, as well as lozenge trials containing 190 mg of zinc per day. This is a 4,300-fold difference in dosage. They argued that this rendered the outcome of the analysis meaningless.

In contrast, Hemilä and Chalker, restricted their analysis to Zinc lozenges in adults, where the evidence is strongest. They concluded that zinc lozenges reduced the duration of colds by 37%. This is a highly statistically significant outcome.

This would mean that, instead of taking a full seven days to recover from a cold, it might take just four and a half days.

However, there’s a caveat. This effect was evident in adults, but not in children. The only major trial conducted in children showed no significant effect, which could indicate that zinc lozenges have a different mechanism of action in younger immune systems or that more research is needed in children.

Does Zinc Really Work?

-Adults: Based on the best available evidence, zinc works for adults, but with some caveats. Zinc lozenges, especially those containing zinc acetate or zinc gluconate in doses above 75 mg per day of elemental zinc, do seem to have a significant effect on shortening the duration of the common cold in adults.

-Kids: For kids, the jury is still out. The evidence for kids is mixed and much weaker. Most pediatricians would not recommend zinc lozenges for kids based on the current evidence.

-Prevention: For prevention, probably not. The evidence for preventing colds in the first place is much weaker than the evidence for treatment. Taking zinc daily as a cold preventative is not supported by the evidence.

-Timing matters: One gets the most benefits from zinc intake when you start the zinc within the first 24 hours of symptoms. If you wait two or three days, it looks like the window of benefit has closed.

Zinc in lozenge form: It also matters that the zinc is in lozenge form, which you can dissolve slowly in your mouth. Taking a zinc supplement in the form of a tablet that you swallow has been shown to have no effect on the duration of a cold. The important thing is getting it to the area of the throat and upper airway.

Nasal sprays: These have been shown to be inconsistent and come with a serious side effect of loss of smell.

Side Effects of Zinc

Zinc is not without its side effects, and it is important to know these before you reach for the lozenge.

-Common side effects: The symptoms that have been most commonly reported include unpleasant taste, nausea, and metallic sensation in the mouth. These are normally mild and can be easily endured.

-Anosmia or loss of smell: The more serious problem is that of zinc-induced anosmia, or the permanent loss of the sense of smell. This has been directly linked to certain zinc nasal spray products and has resulted in massive product recalls and lawsuits in the United States. The FDA has issued a warning about nasal Zinc products in 2009.

-Hinders copper absorption: Long-term high-dose zinc consumption has negative effects on copper absorption. Zinc supplements are not recommended for regular use but only when suffering from an active cold.

Tips on How to Use Zinc

·       Adults should use zinc lozenges for cold treatment.

·       The best time to take a medication is within 24 hours of starting symptoms.

·       The proper way to use lozenges is through mouth sucking not tablet swallowing.

·       The recommended lozenges should contain zinc acetate or zinc gluconate with a minimum of 13-15 mg elemental zinc per lozenge.

·       Avoid nasal zinc sprays because these sprays can cause people to lose their ability to smell.

·       Don't use zinc supplements for more than two weeks without taking a rest period.

·       You must consult your doctor before taking any medication if you are pregnant or breastfeeding or using any drugs.

After nearly four decades and numerous clinical trials, here is where science stands on zinc and the common cold: it is not a magic bullet, but it is not a snake oil either, unless you are a kid, that is.

The scientific evidence supports your use of zinc lozenges if you experience early symptoms of a cold. You should understand that a lozenge will not provide complete healing. The most effective remedies, experts say, for colds require patients to take rest and consume fluids and wait for their full recovery.

Disclaimer: This content is for general informational purposes only and should not replace professional medical advice. Always consult a qualified healthcare provider with any questions about your health or treatment options.