In 1771, German physician Hieronymus David Gaubius introduced "a drug with many hopes" to the Western scientific community-zinc.

More than 200 years later, we can find it in many supplements on the shelves of pharmacies. It is even considered one of the rare things that may help fight the common cold. Or is it?

Evidence on the use of zinc supplements is limited, the results of the study are mixed, and so far there has been no proper investigation of the dosage, formulation and length of the prescription.

A new meta-analysis of 28 randomized controlled trials now reinforces the idea that zinc supplementation can prevent symptoms and shorten the duration of viral respiratory infections such as the common cold or flu.

"It is generally believed that the role of zinc in preventing and treating infections is only applicable to people who are zinc deficient; our findings really challenge this view," said Jennifer Hunter, PhD of General Medicine at the University of Western Sydney in Australia.

"Two large trials from China found that extremely low-dose zinc nasal sprays can reduce the risk of clinical disease. Two smaller trials evaluating the preventive effects of oral zinc in the United States excluded people with zinc deficiency.

"All other trials evaluating zinc in the treatment of the common cold are conducted in people who are extremely unlikely to be zinc-deficient." 

When zinc was used as a preventive measure, the analysis found that the risk of mild symptoms was reduced by 28%, and the risk of moderately severe symptoms was reduced by 87%.

As a treatment taken after illness, zinc has also been found to slightly reduce the duration of symptoms. Usually, taking zinc will reduce the most severe symptoms by about two days.

This is a fairly small effect, especially when you consider that the symptoms are still the same overall. More importantly, if a patient is deliberately infected with a cold virus, zinc cannot prevent them from contracting the disease.

This analysis is an interesting step forward, but the researchers also warn that some of the studies are small, did not compare the same doses, and may have bias in reporting symptoms. This is something that must always be kept in mind when doing meta-analysis-the resulting data is only as reliable as the input.

In addition, although these findings are interesting, they do not tell us how zinc actually suppresses viral infections such as colds.

In the late 18th century, when Gaubius provided the "secret medicine" he "discovered", the zinc sold by alchemists was mainly used to treat severe convulsions. However, when Gaubius got the powder, he found that it was nothing more than zinc oxide. 

For a period of time in the 19th century, zinc was used to treat epilepsy, but by the 20th century, this drug has gradually faded out of sight.

It was not until the 1960s that zinc reappeared as a potential treatment for natural zinc deficiency and a rare genetic disease called Wilson's disease, which causes the accumulation of copper in vital organs. As an anti-copper agent, zinc has been proven to be a very effective treatment for this neurological disease.

However, its potential in combating viral infections is still largely unrealized.

Despite this, some health guidelines recommend that people who fight lower respiratory tract infections take zinc by mouth, and the recent COVID-19 pandemic has made its potential once again manifest.

Although the results of several randomized controlled trials have not yet been announced, some health care workers have begun to use zinc to treat COVID-19. 

If the patient is screened correctly and the dose is not too high, the risk is low. Unless a person suffers from a certain disease that causes zinc in the body to penetrate into the brain, taking this supplement will hardly cause serious health effects.

However, certain doses of zinc may cause non-serious side effects, such as nausea, or using too much zinc nasal spray can cause loss of smell. In general, we still don't know the best way to take zinc.

"Clinicians and consumers need to be aware that there are still considerable uncertainties in the clinical efficacy of different zinc formulations, dosages and routes of administration," Hunter said.

"There is not enough research to say whether zinc nasal sprays, nasal gels, lozenges, and oral zinc are better or worse than other products. Most trials use zinc gluconate or zinc acetate formulations, but this does not mean Other zinc compounds are less effective."

We just need more research. Kobius would definitely agree.

The research was published on BMJ Open.