Quercetin, a flavonoid (plant pigment) found in many plants and foods such as onions, green tea, apples, red leaf lettuce, and berries, has antioxidant and anti-inflammatory effects that, according to WebMD, help reduce swelling, kill cancer cells, control blood sugar, and help prevent heart disease. Now, quercetin is being studied regarding its benefits in fighting SARS-CoV-2 and is showing similar effects as hydroxychloroquine.

Modern Discontent, an independent publisher of scientific papers on COVID-19, has posted an anthology series on quercetin and its benefits in relation to COVID. In this series, Modern Discontent reviews how quercetin helps shuttle zinc, which has antiviral activity, into the cell. It has also been shown (via a computer-modeled study) to inhibit SARS-CoV-2 spike protein to ACE2 receptor docking, which helps prevent viral attachment and thus viral entry into the cell.

The Epoch Times summarizes additional findings, including the following:


  • Inhibits lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNF-α) production in macrophages. (TNF-α is a cytokine involved in systemic inflammation, secreted by activated macrophages, a type of immune cell that digests foreign substances, microbes, and other harmful or damaged components.)
  • Inhibits the release of proinflammatory cytokines and histamine by modulating calcium influx into the cell.
  • Stabilizes mast cells and regulates the basic functional properties of immune cells, thereby allowing it to inhibit “a huge panoply of molecular targets in the micromolar concentration range, either by down-regulating or suppressing many inflammatory pathways and functions.”
  • Acts as a zinc ionophore, i.e., a compound that shuttles zinc into your cells. This is one of the mechanisms that can account for the effectiveness seen with hydroxychloroquine, which is also a zinc ionophore.
  • Boosts interferon response to viruses, including SARS-CoV-2, by inhibiting the expression of casein kinase II (CK2) — CK2 is an enzyme that is fundamental to controlling homeostasis at the cellular level. There is evidence that it down-regulates the ability a cell has to generate Type 1 interferon when attacked by a virus. However, the interferon does not function by attacking the virus. Instead, it tells the infected cell and the cells that surround the infected cell to make proteins that stop viral replication. In a nutshell, quercetin stops CK2 from interfering with the action of Type 1 interferon so cells receive the signal to stop viral replication.
  • Modulates NLRP3 inflammasome, an immune system component involved in the uncontrolled release of proinflammatory cytokines that occurs during a cytokine storm.
  • Exerts a direct antiviral activity against SARS-CoV — Quercetin’s general antiviral capacity has been attributed to three primary mechanisms of action:
    • (1) Binding to the spike protein, thereby inhibiting its ability to infect host cells
    • (2) Inhibiting replication of already infected cells
    • (3) Reducing infected cells’ resistance to treatment with antiviral medication
  • Inhibit the SARS-CoV-2 main protease.

Also included in this anthology are reports of clinical trials related to this drug in the context of COVID-19. In the first study, while it did not test quercetin in isolation, it showed that people who took quinine drops and quercetin had a lower incidence of COVID-19 than the control group. In another trial, 76 participants with COVID were treated with quercetin, and another 76 were only given standard of care. In the quercetin group, only 9.2% of participants needed hospitalization, while in the control group, 28.9% were hospitalized.

According to the authors’ conclusion,


“The results revealed a reduction in frequency and length of hospitalization, in need of non-invasive oxygen therapy, in progression to intensive care units and in number of deaths. The results also confirmed the very high safety profile of quercetin and suggested possible anti-fatigue and pro-appetite properties. QP [Quercetin Phytosome®] is a safe agent and in combination with standard care, when used in early stage of viral infection, could aid in improving the early symptoms and help in preventing the severity of COVID-19 disease.”

The evidence presented by Modern Discontent suggests that quercetin may work similarly to hydroxychloroquine when treating COVID. The drug itself is easier to obtain than hydroxychloroquine and may provide similar early-treatment benefits when used against the virus.

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