Can zinc supplements protect against coughs, colds, flu, and COVID-19?

Zinc helps our immune systems to fight upper respiratory tract infections (URTIs) such as coughs, colds, and flus including COVID-19. In light of the COVID-19 pandemic, new research suggests that taking zinc supplements may help both to prevent and to reduce the length of these illnesses.

What are the benefits of taking zinc?

Zinc plays an important role in our bodies' biological functions, including our immune system, inflammation, tissue injury, blood pressure, and our tissue responses to a lack of oxygen (hypoxia). As such, zinc is essential for taste, smell, vision, growth, cell-building, the healing of wounds, and our immunity from infections.

As zinc is known to modulate immunity, the COVID-19 pandemic has generated considerable interest in zinc for the possible prevention and treatment of COVID-19, as well as other upper respiratory tract infections (URTIs). URTIs are usually caused by viruses and they include coughs, colds, flu, throat infections and sinus infection.

Most URTIs will clear up by themselves, but some - like COVID-19 - may require treatment and can lead to mortality. While there have been studies that suggest zinc may be effective in preventing and fighting URTIs, good-quality evidence had been limited.

Despite the lack of data, many healthcare experts consider zinc supplementations to be a promising treatment for COVID-19. According to one 2020 study, a good indication of this is that most of the high-risk groups for zinc deficiency and for severe COVID-19 are the same. These groups include:

  • The elderly.
  • People with immune deficiency.
  • People who are obese.
  • People with diabetes.
  • People with atherosclerosis (the thickening of the inner artery walls).

Zinc supplements may prevent URTI symptoms and shorten duration

New research published in November 2021 suggests that zinc supplements, such as zinc lozenges, may help stave off symptoms of URTIs, and also reduce the length of time that a person is ill. The research included 28 clinical trials involving 5,446 adults.

Significantly, these results were seen in adults who were unlikely to be zinc deficient. This suggests that zinc supplements may be used by anyone to reduce the risk from COVID-19, as well as from common colds, flu, and coughs.

Trial results

The most common form of zinc supplements tested in the trials were zinc lozenges, followed by nasal sprays and gels. While this did result in a variation of the doses of zinc used, many of the trials produced similar outcomes. Analysis of the trials found that:

  • Zinc lozenges or nasal sprays prevented URTIs in 5 out of 100 people a month.
  • Symptoms typically cleared up two days earlier when a zinc spray or liquid was taken under the tongue (known as a sublingual form).
  • Participants who used a sublingual or nasal spray were twice as likely to recover during the first week of illness, and almost 20% were more likely to recover during the second week.
  • Zinc supplements had a significant effect on symptom reduction on the third day of illness.

"The marginal benefits, strain specificity, drug resistance, and potential risks of other over-the-counter and prescription medications make zinc a viable 'natural' alternative for the self-management of non-specific respiratory tract infections," believe the researchers.

"Zinc also provides clinicians with a management option for patients who are desperate for faster recovery times and might be seeking an unnecessary antibiotic prescription," they add.

Side-effects and limitations of zinc supplements

No serious side-effects were reported, although researchers noted a 40% increase in the risk of temporary side-effects such as nausea and irritation of the nose or mouth.

There were also some notable limitations regarding the effectiveness of zinc supplements in protecting from respiratory tract infections.

  • While zinc supplements can help reduce symptoms on day 3 of the illness, there was no evidence that zinc helped to ease symptoms daily.
  • There was no evidence that zinc reduced the risk of developing an infection or cold symptoms when a participant had human rhinovirus (rhinovirus infections are a major causes of the common cold, and can also cause sore throats, ear infections, infections of the sinuses, pneumonia, and bronchiolitis).
  • Participants with human rhinovirus also didn't have a reduced length of illness when taking zinc.

It should also be noted that the researchers advise of two important limitations of the research itself: "The comparative effectiveness of different zinc formulations and doses was unclear” and "The GRADE-certainty/quality of the evidence was limited by a high risk of bias, small sample sizes and/or heterogeneity."

Clinical uncertainty remains around the efficacy of different forms of zinc supplements, how they are administered, and the appropriate size of the doses. Further research is needed before zinc supplements can be recommended as a treatment for upper respiratory tract infections.

Potentially preventing and treating COVID-19 with zinc

More research into the role of zinc in protecting against COVID-19 is also needed. None of the trials specifically examined the use of zinc for the prevention and treatment of COVID-19.

However, there are some promising indications for the use of zinc to treat COVID-19. The results of three trials did suggest that zinc was most effective when used to reduce the risk of more severe symptoms, such as a fever and flu-like illnesses.

Likewise, in other recent data, experts have been considering the indirect indications that zinc may be an effective therapy for COVID-19. It appears that higher levels of zinc may protect against severe COVID-19 by:

  • Reducing lung inflammation.
  • Improving the lung's defence against harmful substances through mucus.
  • Preventing ventilator-induced lung injury.
  • Modulating antibacterial and antiviral immunity.

However, it is important to note that extremely high levels of zinc intake can result in toxicity.

Also of note, zinc was earlier suggested as a possible way to prevent and fight against 'swine flu' (H1N1 influenza).

Although more substantial and direct research is required, zinc supplementation holds a lot of promise as a future treatment for COVID-19. This could be a significant development, as aside from vaccinations, prevention and treatment options are currently limited to hygiene and social distancing measures, reducing dangerous antibiotic use, and over-the-counter medications to treat symptoms.

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