In 1771, the German physician Hieronymus David Gaubius introduced the Western scientific community to “a medicine with many promises” – zinc.
More than 200 years later, we can find it among the many supplements on pharmacy shelves. It is even known to be one of the rare things that can help fight a common cold. Or does it?
Evidence for the use of zinc supplements has been limited, study results have been mixed, and dosage, formulation, and prescription length have not been properly studied to date.
A new meta-analysis of 28 randomized controlled trials has now strengthened the notion that zinc supplementation can prevent symptoms and shorten the duration of viral respiratory infections, such as the common cold or flu.
“It is widely believed that the role of zinc in the prevention and treatment of infections is only for people who are deficient in zinc; our findings really challenge this view,” said Jennifer Hunter, MD of Western Sydney University in Australia.
The two large trials from China found that very low-dose zinc nasal sprays reduced the risk of clinical disease. The two smaller trials in the United States that evaluated the preventive effects of oral zinc excluded people with zinc deficiency.
“All the other trials that evaluated zinc to treat the common cold were in populations where zinc deficiency is highly unlikely.”
When zinc was taken as a preventative measure, the analysis found that there was a 28 percent lower risk of developing milder symptoms and an 87 percent lower risk of developing moderately severe symptoms.
As a treatment, taken after by getting sick, it also turned out that zinc slightly reduced the time the symptoms persisted. Usually, taking zinc reduced the worst symptoms by about two days.
This is a fairly minimal effect, especially considering that the symptoms remained just as severe in general. What’s more, if the patient is purposefully infected with a cold virus, zinc does not prevent them from contracting the disease.
This analysis is an exciting step forward, but the researchers also warn that some of the included studies were small, did not compare the same doses, and could include bias in the reporting of symptoms. This is something to always keep in mind when performing meta-analyzes – the resulting data will only be as reliable as the input.
While the results are interesting, they may not tell us much about how zinc actually slows down a viral infection like a cold.
Before the end of the 18th century, when Gaubius offered the ‘secret substance’ he had ‘found’, zinc was mostly sold by alchemists to treat severe seizures. When Gaubius got his fingers in the powder, however, he discovered that it was nothing but zinc oxide.
For a while in the 19th century, zinc was used to treat epilepsy, but by the 20th century, the medicine had faded out of popularity and out of our minds.
It was not until the 1960s that zinc re-emerged as a potential treatment for natural zinc deficiency and a rare inherited disorder called Wilson’s disease, which causes a buildup of copper in vital organs. As an anti-copper agent, zinc has since been shown to be quite an effective treatment for this neurological disease.
When it comes to fighting viral infections, its potential remains largely unrealized.
Nevertheless, some health guidelines recommend oral zinc for those fighting lower respiratory tract infections, and the recent COVID-19 pandemic has brought its potential forward again.
Despite pending results from a few randomized controlled trials, some healthcare professionals have already started using zinc as a treatment for COVID-19.
The risk is low if the patient is screened correctly and the dosage does not become too high. Unless a person has a disorder that allows bodily zinc to filter into the brain, there are almost no serious health effects of taking the supplement.
However, some doses of zinc can come with non-serious side effects, such as nausea or, as it is common to use too much zinc nasal spray, a loss of odor. And in general, we still do not even know what is the best way to take zinc.
“Clinicians and consumers need to be aware that there is still considerable uncertainty regarding the clinical effect of different zinc formulations, doses and routes of administration,” says Hunter.
“Currently, there is just not enough research to say whether a zinc nasal spray versus a nasal gel versus a lozenge versus oral zinc is better or worse than the others. Most of the trials used zinc gluconate or zinc acetate formulations, but that does not mean that others zinc compounds are less effective. “
We simply need more research. Gaubius would certainly agree.
The study was published in BMJ open.