Quercetin and COVID-19: Studies Found that Quercetin Might Be Helpful as Prevention
What is Quercetin?
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:
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 ActionAs 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.
“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 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 VirusesBefore 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)
•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.27As reported by the authors of this study:
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
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 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
- 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
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).
- 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.
- 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.
- 1 Drmurray.com
- 2, 4 International Journal of General Medicine June 2021; 14: 2807-2816
- 3 International Journal of General Medicine June 8, 2021; 14: 2359-2366
- 5 International Journal of General Medicine June 8, 2021; 14: 2359-2366 (Full)
- 6 Journal of Natural Health Product Research July-December 2021; 3(2) Rationale for Quercetin as a Potential Supplement to Increase Resistance to COVID
- 7 American Journal of Physiology August 1, 2008
- 8 Journal of the American Dietetic Association 2011 Apr;111(4):542-9
- 9, 10, 19, 20 Journal of Infectious Diseases and Preventive Medicine May 24, 2014; 2: 111
- 11 Antiviral Research June 2012; 94(3): 258-271
- 12 Journal of Ancient Diseases & Preventive Remedies 2014
- 13 Viruses 2016 8(1), 6
- 14 European Journal of Pharmaceutical Sciences June 28, 2009; 37(3-4): 329-333
- 15 Antiviral Research 2010 Nov;88(2):227-35
- 16 Experimental Lung Research 2005; 31(5)
- 17 Journal of Agricultural and Food Chemistry 2016; 64(21): 4416-4425
- 18 Viruses 2016 Jan; 8(1): 6
- 21 Journal of Medical Virology January 1985 DOI: 10.1002/jmv.1890150110
- 22 Asian Pacific Journal of Tropical Medicine January 2016; 9(1): 1-7
- 23 Virologica Sinica August 2015; 30(4): 261-268
- 24 Hepatology 2009 Dec;50(6):1756-64
- 25, 28 Microbial Pathogenesis March 2020; 140: 103934
- 26 Clinical & Experimental Immunology November 2004; 138(2): 195-201
- 27 CDC Pneumococcal Disease
- 29 Nutrients 2016 Mar; 8(3): 167, 5.2.1 Animal Models
- 30, 32 Nutrients 2016 Mar; 8(3): 167, 5.1.2 Mechanism of Action
- 31 Nutrients 2016 Mar; 8(3): 167, Table 1: Mast cell
- 33 Journal of Natural Health Product Research July-December 2021; 3(2)
- 34 Genetic Lifehacks December 17, 2019
- 35 J Am Heart Assoc. 2016 Jul 12;5(7). pii: e002713
- 36 Nutrition Reviews January 6, 2020 DOI: 10.1093/nutrit/nuz071
- 37 Int J Mol Sci. 2019 Dec 3;20(23). pii: E6093
- 38 Obesity (Silver Spring). 2008 Sep;16(9):2081-7
- 39 Phytotherapy Research March 8, 2019; 33(5)
- 40 Scientific Reports April 12, 2016; 6 Article Number: 24049
- 41 Phytotherapy Research August 26, 2019 DOI: 10.1002/ptr.6486
- 42 Br J Nutr. 2016 Mar 14;115(5):800-6
- 43 J Am Coll Nutr. 2017 Jan;36(1):9-15
- 44 Fitoterapia 2015 Oct;106:256-71
- 45 Neuroscience 2016 Jun 2;324:163-76
- 46 EBioMedicine. 2019 Sep;47:446-456
- 47 BMB Rep. 2019;52(1):47–55
- 48 Molecules 2019 Dec 23;25(1). pii: E63