Quercetin and COVID-19: Studies Found that Quercetin Might Be Helpful as Prevention

By Dr Frank Yap, M.D. - July 14, 2022

As of July 2022, there have been 9 published studies of quercetin and COVID-19 (c19quercetin.com).

Quercetin is also no. 1 in this prevention studies league table:

What is Quercetin?

Quercetin is a pigment that is found in plants, vegetables, and fruits, and serves as an immune nutrient offering many health benefits. Elderberry, red onions, white onions and cranberries are the richest sources of quercetin. It is a flavonoid and antioxidant that may help to reduce inflammatory cytokines, infections, allergies and anti-blood clot property. Research has found that quercetin may be particularly beneficial for viral respiratory infections. This is definitely one nutrient you can consider seriously to add to the growing number of strategies you can use to treat or prevent COVID-19.

Can Quercetin Reduce Hospitalizations and Deaths?

In one early treatment study — a prospective, randomized, controlled and open-label trial — gave 152 COVID-19 outpatients a daily dose of 1,000 mg of quercetin for 30 days to evaluate its adjuvant effects in the treatment of early symptoms and the prevention of severe infection. According to the authors:

“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. It is suggested that a double-blind, placebo-controlled study should be urgently carried out to confirm the results of our study.”

Each tablet (Quevir®, a dietary supplement notified by Pharmextracta S.p.A., Italy, contained 500 mg of Quercetin Phytosome® (QP) developed by Indena S.p.A., Milan, Italy. Quercetin Phytosome corresponded to 200 mg of quercetin; therefore, each daily treatment corresponded to 400 mg of quercetin.

Mechanisms of Action

As noted in this study, quercetin was chosen based on the fact that it has antiviral, anti-blood clotting, anti-inflammatory and antioxidant properties, all of which are important in the treatment of SARS-CoV-2 infection.

In this publication, more detailed mechanisms of action are reviewed. According to the authors:

“SARS-CoV-2 proteases, like 3-chymotrypsin-like protease (3CLpro), papain-like pro-tease (PLpro), RNA-dependent RNA polymerase, spike (S)protein and human angiotensin-converting enzyme 2 (hACE2) are considered possible targets for developing effective anti-COVID-19 drugs.

Recently, molecular docking studies have suggested the possible binding interaction of quercetin with the 3CLpro, PLpro, and S-hACE2 complex. Some recent results, obtained by biophysical techniques, appear to support the results of the molecular docking studies.

Quercetin, a flavonol not naturally present in the human body, is the most abundant polyphenol in fruits and vegetable and is widely used as a dietary supplement to boost the immune system and promote a healthy lifestyle.

Quercetin is characterized by three crucial properties: antioxidant, anti-inflammatory and immunomodulatory. The combination of these actions allows quercetin to be a potential candidate to support all unhealthy conditions where oxidative stress, inflammation and immunity are involved.”

Initially, quercetin gained attention because it’s a zinc ionophore, meaning it shuttles zinc — which has well-known antiviral effects — into your cells just like the drug hydroxychloroquine.

Some proposed the primary reason hydroxychloroquine and quercetin worked was because of this feature. Of course, you also had to take zinc along with either of them. To effectively act as a zinc ionophore, quercetin also needs vitamin C.

Since then, other studies, including the two reviewed here, have shown quercetin has other actions that makes it useful against SARS-CoV-2 as well. As reported by Murray in his newsletter:

“In particular, quercetin exerts significant inhibition on the binding of specific spike proteins to ACE-2 receptors, thereby blocking the ability of the virus to infect human cells. Quercetin has also been shown to directly neutralize viral proteins the are critical in the replication of SARS-CoV-2.”

In some studies, quercetin has also been shown to inhibit the release of inflammatory cytokines, which could help alleviate infection-related symptoms and suppress excessive inflammatory responses from occurring.

Its antioxidant effects may also help prevent tissue damage caused by scavenging free radicals, thereby aiding in the recovery process of viral infections.6

Quercetin’s Antiviral Properties

Quercetin’s antiviral properties have been attributed to three main mechanisms of action:

Inhibiting the virus’ ability to infect cells
Inhibiting replication of already infected cells
Reducing infected cells’ resistance to treatment with antiviral medication

For example, research7 funded by the U.S. Defense Advanced Research Projects Agency (DARPA), published in 2008, found it lowers your risk of viral illness such as influenza and boosts mental performance following extreme physical stress, which might otherwise undermine your immune function and render you more susceptible to infections.

Here, cyclists who received a daily dose of 1,000 mg of quercetin in combination with vitamin C (which enhances plasma quercetin levels8,9) and niacin (to improve absorption) for five weeks were significantly less likely to contract a viral illness after bicycling three hours a day for three consecutive days, compared to untreated controls. While 45% of the placebo group got sick, only 5% of the treatment group did.

Quercetin Works Against Many Common Viruses

Before the COVID-19 pandemic struck, several studies had highlighted quercetin’s ability to prevent and treat the common cold and seasonal influenza. (10,11,12,13,14,15,16,17,18)

By attenuating oxidative damage, it also lowers your risk of secondary bacterial infections,19 which is actually the primary cause of influenza-related deaths.

Importantly, quercetin increases mitochondrial biogenesis in skeletal muscle, which suggests part of its antiviral effects are due to enhanced mitochondrial antiviral signaling.20 Quercetin also works against other viruses, as demonstrated in the following studies:

•A 1985 study found quercetin inhibits infectivity and replication of herpes simplex virus type 1, polio-virus type 1, parainfluenza virus type 3 and respiratory syncytial virus (RSV).21

•A 2016 animal study22 found quercetin inhibited mouse dengue virus and hepatitis virus.

•Other studies have confirmed quercetin’s power to inhibit both hepatitis B23 and C24 infection.

•A March 2020 study25 found quercetin provides “comprehensive protection” against Streptococcus pneumoniae infection, both in vitro and in vivo, primarily by neutralizing pneumolysin (PLY),26 one of the toxins released from pneumococci that encourages S. pneumoniae infection to blossom in the first place.

Streptococcus pneumoniae is responsible not only for pneumonia, but can also be involved in some ear and sinus infections, meningitis and certain blood infections.27

As reported by the authors of this study:

“The results indicated that quercetin significantly reduced PLY-induced hemolytic activity and cytotoxicity via repressing the formation of oligomers.

In addition, treatment with quercetin can reduce PLY-mediated cell injury, improve the survival rate of mice infected with a lethal dose of S. pneumoniae, alleviate the pathological damage of lung tissue and inhibit the release of cytokines (IL-1β and TNF-α) in bronchoalveolar lavage fluid. Considering the importance of these events in antimicrobial resistant S. pneumoniae pathogenesis, our results indicated that quercetin may be a novel potential drug candidate for the treatment of clinical pneumococcal infections.”

How Quercetin Combats Inflammation and Boosts Immunity

Aside from its antiviral activity, quercetin is also known for boosting immunity and combating inflammation. As noted in a 2016 study29 in the journal Nutrients, mechanisms of action include (but is not limited to) the inhibition of:30

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
LPS-induced mRNA levels of TNF-α and interleukin (IL)-1α in glial cells, which results in “diminished apoptotic neuronal cell death”
The production of inflammation-producing enzymes
Calcium influx into the cell, which in turn inhibits pro-inflammatory cytokine release, as well as histamine and serotonin release from intestinal mast cells31

According to this paper, quercetin also stabilizes mast cells, has cytoprotective activity in the gastrointestinal tract, and “a direct regulatory effect on basic functional properties of immune cells,” which allows 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.”32

Bioavailability

While quercetin does have potent antiviral effects, in order for it to work effectively you need sufficiently high dosages to raise the level of quercetin in your body’s tissues.

The relatively low absorption rate of quercetin is why a sunflower lecithin formulation was used.

Research33 published in the July-December 2021 issue of the Journal of Natural Health Products Research, found a quercertin matrix has the same total absorption rate as quercetin phytosome — and higher peak blood levels.

“Since both of these forms of quercetin produce similar blood levels, they should produce the same effects at equal dosages based upon quercetin content,” Murray wrote in his newsletter, adding:

“My dosage recommendation as part of a nutritional supplement program to support immune function is 250 mg twice daily.

And in patients with active Infection, my recommendation is … six capsules twice a day providing a total of 3,000 mg of quercetin. This high dosage should be taken for at least 10 days and then reduced to a maintenance dosage of 250 mg twice daily …

[This] high dosage may not be necessary. But my dosage calculations are based upon likely tissue concentrations needed to exert the strongest antiviral effects. And given the safety of quercetin, there is no harm at this level.”

Protocols Using Quercetin

One doctor who early brought quercetin into the limelight was Dr. Vladimir Zelenko. As hydroxychloroquine became difficult to obtain, Zelenko switched to recommending quercetin instead, as it’s readily available as an over-the-counter supplement. For more details of Zelenko’s protocol for COVID-19, visit Zelenko Protocol.

Other prominent protocols that recommend quercetin include the FLCCC's I-PREVENT and I-CARE protocols.

Other Health Benefits of Quercetin

There are also other lesser known benefits and uses for quercetin, including the prevention and/or treatment of:34

High blood pressure35,36
Cardiovascular disease37
Obesity38 and metabolic syndrome39 (a cluster of conditions including high blood pressure, high blood sugar, high triglyceride levels and fat accumulation around the waist that raise your risk for Type 2 diabetes, heart disease and stroke)
Certain kinds of cancer, in particular leukemia, and to a lesser degree breast cancer40
Nonalcoholic fatty liver disease (NAFLD)41
Gout42
Arthritis43
Mood disorders44
Aluminum-induced neurodegenerative changes, such as those seen in Alzheimer’s, Parkinson’s and amyotrophic lateral sclerosis (ALS).45
Longevity, thanks to its senolytic benefits (clearing out damaged and worn-out cells)46,47

Research has also highlighted quercetin’s epigenetic influence and ability to:48

Interact with cell-signaling pathways
Modulate gene expression
Influence the activity of transcription factors
Modulate microRNAs

MicroRNAs used to be considered "junk" DNA. But far from being useless, research has revealed so-called "junk" DNA is actually microRNA and plays a crucial role in regulating genes that make the proteins that build your body.

The microRNA function as "on/off" switches for the genes. Depending on the microRNA input, a single gene can code for any of more than 200 protein products. Quercetin’s ability to module microRNA may also help explain its cytotoxic effects, and why it appears to improve cancer survival (at least in mice).

Key Takeaways

Aside from supplements and preventive treatments, there are other ways that may help improve immune response and to prevent you from catching the coronavirus.

Abundant evidence suggests that eating whole in fruits, vegetables and whole grains—all rich in networks of naturally occurring antioxidants and their helper molecules—provides protection against free radicals.
Vaccination
Getting Enough Sleep
Avoid sugar, red meat and processed foods.
Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.
Try to minimize stress.
Drink enough water to keep your body hydrated.
Avoid drinking excess alcohol and stop smoking.
Avoid crowded areas especially in-door.
Regular outdoor physical activity. (Ref)
Wear protective face mask. This is to protect not only yourself but others.
Consult your nearest local healthcare provider if you have any doubt.

Sources and References

Original Article: https://articles.mercola.com/sites/articles/archive/2021/10/14/quercetin-improves-covid-outcomes.aspx

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