Quercetin 101 : Here's What You Need to Know (2022)
Table of Content:
1. What is Quercetin?
Quercetin is a pigment that belongs to a group of plant compounds called flavonoids (also known as bioflavonoids). Flavonoids are naturally present in fruits, grains, teas, and wine. Researchers have linked flavonoids to a variety of benefits, including a reduced risk of heart disease, cancer, and degenerative brain disorders.
Specifically, research also says that quercetin supplementation is best achieved when consumed with a fat-enriched diet.
Quercetin goes by a number of different names. You might see quercetin supplements labeled as bioflavonoid concentrate, bioflavonoid extract, or citrus bioflavonoid, for example.
Most supplement companies use various plant or vegetable-based sources of quercetin. Check the label.
Some quercetin supplements are specifically marketed as citrus-free, making them ideal for those with citrus sensitivities. Read the label or official product website for your supplement to be sure that it is actually citrus-free.
Quercetin supplements are generally labeled non-GMO. Check the label to verify your quercetin supplement is not made from genetically modified ingredients.
2. Benefits of Quercetin Supplements
Quercetin has been linked to the following health benefits:
- Possessing anti-inflammatory, antioxidant properties that can help combat certain diseases. One study found that 500 mg of quercetin a day could improve symptoms of rheumatoid arthritis.
- Helping prevent cancer cell growth from breast, colon, prostate, endometrial and lung.
- Counteracting allergic reactions and helping with immune responses.
- Helping to prevent osteoporosis
- Addressing cognitive decline, including Alzheimer’s and dementia.
- Assisting in control of blood pressure. A study in 2002 found that quercetin can have vasodilator effects.
- Potentially helping to lower blood sugar levels. One study found that dosages of 500 mg per day “significantly reduced” fasting glucose levels.
Quercetin is a natural antihistamine and anti-inflammatory plant pigment that boosts your immune system and may work to control viral replication, according to some research. It helps to couteract allergic reactions and helping with immune responses. It allows zinc to exert its proven antiviral properties.
i. How Does Quercetin Manage Allergy Symptoms?
Studies have shown that quercetin stabilizes mast cells that release histamine. Histamine is the principal mediator of reactions to pollen and other allergies. This makes quercetin a natural antihistamine. Many people use quercetin to treat symptoms of hay fever, including runny nose, watering eyes, and itching.
McCullough et al. Reviews in Cardiovascular Medicine, 2020
ii. Quercetin Benefits for Inflammation
Flavonoids (aka bioflavonoids) including quercetin, are key anti-inflammatories that act as antioxidants, which means they fight the natural process of oxidation that takes place over time as we age. Quercetin can help stop damaging particles in the body known as free radicals, which negatively impact how cells work. It can also reduce expression of inflammatory genes such as interleukin.
Research now shows that inflammation is the root of most diseases, including heart disease, cancer, cognitive decline, some mental disorders, and autoimmune disorders. At this time, practitioners and patients report using quercetin to effectively fight a variety of conditions related to inflammation, including:
“Hardening of the arteries” (atherosclerosis)
Heart disease and circulation problems
Insulin resistance and diabetes
Eye-related disorders, including cataracts
Allergies, asthma, and hay fever
Chronic fatigue syndrome
Inflammation of the prostate, bladder, and ovaries
Chronic infections of the prostate
Skin disorders, including dermatitis and hives
iii. Quercetin Benefits for Hives
Dr Deborah Gordon recommends trying a food elimination diet to pinpoint the source of the problem. Thus, if you get rid of the source, you won’t have to worry about treating the hives.
Antihistamine drugs also stop the release of the histamines that cause the hives in an allergic reaction. However, people who suffer from chronic hives don’t usually want to take medication for months or years if they don’t have to.
For this reason, some allergy sufferers turn to natural alternatives such as quercetin; that works by stabilizing the membranes of cells that release histamine. This often helps brings inflammatory and allergic reactions under control. You can buy quercetin products in natural foods stores or Amazon. The best form is a coated 400 mg tablet, taken twice a day between meals; as recommended by Dr Andrew Weil. It can take six to eight weeks of continuous use for quercetin to build up to therapeutic levels in the body.
iv. Does Quercetin Help Allergies? : Research Studies
Quercetin has been shown to reduce inflammation in multiple studies. In this 8 week study involving 50 women with rheumatoid arthritis, participants took 500mg of quercetin per day or a placebo. The quercetin group reported less early morning stiffness, morning pain, and after-activity pain.
Early studies on quercetin and inflammation are promising, although more large scale human studies need to be performed to verify these benefits.
There’s evidence that quercetin reduces allergy symptoms. Researchers believe quercetin’s anti-inflammatory effects may relieve allergy symptoms.
This study published in Molecules in 2016, for example, found that quercetin could be effective for treating the anaphylactic (allergic) reaction in someone with peanut allergies. A similar study from 2006 concluded that quercetin was a “safe, natural therapy that may be used as primary therapy or in conjunction with conventional methods” for blocking allergies.
It’s possible that quercetin has the same anti-allergy effect in humans, although more research needs to be done.
i. Does Quercetin Fight Cancer? : Research Studies
Animal studies suggest that quercetin effectively suppresses breast tumor growth, and further studies demonstrated that quercetin enhanced the therapeutic effects of Adriamycin® while suppressing its toxic effects on normal cells.
An animal study with rats conducted in 2009 demonstrated that quercetin’s antioxidant effects may act to prevent hepatocellular carcinoma (HCC).
This study published in 2017 in Oncology Reports took things a step further, finding that quercetin induced cancer cell death in nine types of cancer, including prostate cancer, colon cancer, and breast caner.
In another 2017 study, researchers gave quercetin to mice with tumors. Researchers found that mice in the quercetin-treated group showed delayed tumor growth, no significant changes in daily behavior, significantly better survival ratings, and increased rates of cell death.
Quercetin may also target bladder cancer. In 2016, researchers published a landmark study in the American Journal of Cancer Research. Researchers analyzed quercetin’s effect on cancer cells in a test tube. They concluded, “We are the first to show that quercetin displays potent inhibition on bladder cancer cells via activation of AMPK pathway.”
Early research on the cancer-fighting benefits of quercetin is promising, although more research needs to be performed to verify these effects in humans.
i. Does Quercetin Reduce the Risk of Alzheimer’s? : Research Studies
In this study published in Neuropharmacology in 2015, researchers gave quercetin to mice with Alzheimer’s, injecting them with quercetin every two days for three months. By the end of the study, the injections had reversed several markers of Alzheimer’s, and the mice performed much better on learning tests.
In a separate study published in 2018, researchers gave mice with Alzheimer’s a quercetin-rich diet. Researchers found the diet improved brain function in mice with early-middle stage Alzheimer’s, although it had no significant effect on middle-late stage Alzheimer’s.
You may have heard that coffee is linked to a reduced risk of Alzheimer’s. There’s certainly some research to back that claim up. However, recent research has suggested that quercetin (not caffeine) is the primary compound in coffee responsible for protective effects against Alzheimer’s.
Research suggests that quercetin reduces blood pressure levels. In this study published in 2002, researchers found that quercetin exhibited vasodilator effects, widening blood vessels and reducing blood pressure.
Multiple studies on humans have suggested similar benefits. Researchers reviewed nine human studies involving 580 people. After reviewing available evidence, researchers found that taking more than 500 mg of quercetin supplement per day reduced systolic and diastolic blood pressure by 5.8mm Hg and 2.6 mm Hg, respectively. In other words, quercetin was shown to significantly improve blood pressure readings.
i. Quercetin Heart Benefits
ii. Quercetin for Cardiovascular Support
Another clinical study demonstrated that quercetin’s antioxidant properties may also reduce the cardiovascular risks of atherosclerosis that patients in end-stage kidney failure typically suffer from. Thirty-eight patients undergoing regular hemodialysis for renal failure were divided into two groups: 26 given 100 ml of concentrated red grape juice (RGJ) a day over two weeks, and the remaining 12 as a control group not taking the RGJ supplement. A group of 15 healthy volunteers were also included in the study. (Reference)
Quercetin is the main polyphenol constituent of RGJ (red grape juice), and results of the study were substantial increases in HDL (the “good” cholesterol) as well as clinically significant decreases in LDL (the “bad” cholesterol), both of which lower the risks of atherosclerosis. Interestingly, even though not show in most previous studies, this study demonstrated the same effects on cholesterol levels in the healthy test subjects as in the unhealthy patients. One explanation may be the substantially higher amount of RGJ supplement given in this study (644 mg/day vs. 432 mg/day). (Reference)
i. Does Quercetin Help with Diabetes? : Research Studies
i. Does Quercetin Work for Anti-aging? : Research Studies
These inconsistent findings from the studies maybe are due to the difference in the range of fitness of the subjects, differences in research design, different methods in the preparation of quercetin extract, etc. In order to assist you in doing your own research, let’s dive into some relevant studies and reviews.
Therefore, consuming it may help people increase their activity throughout the day and delay fatigue. Plus, this can lead to expending more energy during workouts, thus burning more calories.
Dr Josh Axe also adds that some athletic supplements contain quercetin because some people believe that is increases endurance and athletic performance.
It was also discovered that consumption of 500 mg of quercetin twice a day increased the VO2 max (the maximum amount of oxygen that is utilised by an individual) in untrained individuals as a result of an increase in mitochondrial biogenesis.
i. Can Quercetin Help You Recover After Exercise? : Research Studies
Quercetin is added to some athletic supplements because it’s believed to help increase athletic performance and endurance, likely because of its positive effects on blood flow. Researchers from the School of Applied Physiology at the Georgia Institute of Technology found that, on average, “quercetin provides a statistically significant benefit in human endurance exercise capacity (VO2 max) and endurance exercise performance.”
Other studies show that quercetin helps increase immune function and prevents susceptibility to illnesses that can occur when someone trains intensely and experiences exhaustion. One study found evidence that taking a dosage of 500 mg of quercetin twice daily helped protect cyclers from exercise-induced respiratory infections.
Because it can boost energy, quercetin could affect sleep patterns. One study found evidence that it may alter the sleep-wake cycle partly through activation of GABA receptors. However, insomnia is generally not believed to be a common side effect of taking quercetin.
Some studies show that quercetin boosts recovery after exercise. In some small studies, athletes taking quercetin after exercise had faster recovery than a control group. Researchers believe quercetin reduces oxidative stress and post-exercise inflammation, helping your body recover.
In treating COVID-19, quercetin may also lower inflammation, help clear mucus, prevent ventilator-induced damage and support immunity.
i. Can Quercetin Reduce Hospitalizations and Deaths?
ii. Research Studies
Quercetin may help asthma by relaxing smooth muscles lining the airway, improving airway flow.
i. Is Quercetin Good For Herpes?
ii. Quercetin for Canker Sores
In the forty male patients randomly assigned to apply quercetin topical cream 2-3 times a day to canker sores, 90% had completely healed ulcers in 4-7 days. By 10 days, all 20 test subjects had resolved sores. Compared to the control group treated with a medicated mouthwash, the quercetin cream group healed faster and found the cream easy to use.
iii. Quercetin Works Against Many Common Viruses
Capable of blocking “mast cells,” which are immune cells critical in triggering allergic reactions, inflammatory disease, and autoimmune disease, quercetin can help protect skin from the effects of disorders like dermatitis and photosensitivity. Flavonoids like quercetin block the release of many proinflammatory cytokines, such as IL-8 and TNF, which helps stop symptoms related to skin inflammation, even in people who don’t find relief from other conventional treatments or prescriptions.
Studies have found that quercetin has antioxidant and anti-inflammatory effects that help fight allergic and inflammatory diseases as well as some prescriptions when taken in oral supplement form. For example, some people take quercetin for eczema since it can inhibit the secretion of histamine and pro-inflammatory markers.
Recent research has shown that quercetin has protective effects when administered to rats with ethanol-induced acute liver injury. Researchers concluded that “quercetin, by multiple mechanisms interplay, demonstrates hepatoprotective effect on liver-injury induced by alcohol by increasing ethanol metabolizing enzyme activities, increasing antioxidant system activities against oxidative stress, and lowering the expressions of proinflammatory cytokines.”
A 2017 study found evidence indicating that quercetin attenuates liver inflammation and fibrosis in mice through inhibiting macrophages infiltration. Researchers believe it “holds promise as a potential therapeutic agent for human fibrotic liver disease,” a condition triggered by liver injury and inflammation.
3. Quercetin Dosage
Most quercetin studies use a dosage of around 500mg per day, although some studies use a dosage of 500mg taken twice per day.
Most supplements have a similar dosage, offering 500mg to 1,200mg of quercetin per serving.
In some studies, researchers have given participants up to 5,000mg of quercetin per day with no reported side effects.
Quercetin has poor bioavailability. You might take a 1,200mg quercetin supplement, but your body only absorbs a small percentage of it. That’s why many quercetin supplements contain vitamin C or bromelain, as some evidence suggests they boost absorption.
Experts recommend taking 400mg of quercetin twice a day between meals for hay fever. Also consult your doctor to help provide a more comprehensive and effective treatment for hay fever.
The FLCCC I-MASK+ protocol recommends 250 mg/day for COVID-19 prevention and 250 mg twice a day for treatment.
4. Food Sources of Quercetin
You may already get a small amount of quercetin in your normal diet: quercetin is found in onions, kale, tomatoes, broccoli, asparagus, berries, red wine, citrus fruits, cherries, and tea. Many people also take quercetin in supplement form.
In fact, it’s estimated that the average person consumes about 10 to 100 mg of quercetin per day through a normal diet. Quercetin is one of the most abundant flavonoids in the human diet.
What are the best foods for quercetin?
- Organically grown apples, grapes and tomatoes
- Dark cherries and dark berries like blueberries, blackberries and bilberries (eaten in moderation)
- Cocoa, unsweetened
- Hot green chili peppers
The average person gets 10 to 100 mg of quercetin per day through normal dietary sources. This can vary greatly. Carefully track your diet over an extended period to figure out if you have a dietary deficiency of quercetin.
5. Quercetin Supplement Types
What’s better – quercetin tablets, capsules, powders, or liquid?
Quercetin liquid claims to be more bioavailable than other sources of quercetin. You take the liquid sublingually (underneath your tongue). However, limited research shows quercetin capsules or powders are more effective, and all forms of quercetin are absorbed poorly by the body.
6. Quercetin Comparison
Quercetin Dihydrate has the highest bioavailability when it comes to quercetin supplements.
According to Examine.com, this form is preferable to glycosides, aglycone and rutinoside versions.
Additionally, some research indicates that quercetin has a synergistic effect when combined with other flavonoid supplements, such as resveratrol, genistein, and catechins.
Quercetin is found in two forms, including in rutin or glycosidic form. Quercetin glucosides, such as isoquercitrin and isoquercetin, seem to be much more bioavailable and more quickly absorbed than quercetin aglycone or quercetin glycosides, such as rutin (quercetin rutinoside).
Quercetin supplements come in different forms. Most of the quercetin ingredients on the market are in the quercetin dihydrate form. Quercetin anhydrous and dihydrate differ in the amount of water they contain. Quercetin anhydrous contains only 1% to 4% moisture and the sugar molecules that are attached to quercetin in its natural form have been extracted. This translates into 13% more quercetin per gram for quercetin anhydrous vs quercetin dihydrate. For formula manufacturers, this means there is substantially less bulk per capsule or tablet.
i. What is Hydroxychloroquine?
Clinical evidence to date has reported promising results (see above) for Ivermectin in prevention, early treatment as well as late treatment for COVID-19.
While both Ivermectin and Hydroxychloroquine might be useful for early treatment, Ivermectin has a broader potential benefit i.e. prevention, early treatment as well as late treatment / hospital treatment. An important to note is that both ivermectin and hydroxychloroquine perform better when given early (within first 3 – 5 days of symptoms) as opposed to late treatment.
That said, if you simply cannot get hydroxychloroquine or ivermectin, quercetin is a viable stand-in. Quercetin works best when taken with vitamin C and Bromelain, as vitamin C helps activate it and bromelain helps with the absorption.
Although ivermectin and hydroxychloroquine are relatively safe drugs, they are still synthetic chemicals that can have side effects. Quercetin and Vitamin D, C, Zinc are nutrients that your body require for optimal health. Nutrients are safer alternatives especially if your risk is low e.g. age below 50 and no other chronic illness.
Is quercetin Same as Quinine? No. Quercetin is a phytonutrient whereas quinine is a naturally occurring compound found in cinchona bark and was used as an antimalarial agent. However, both quercetin and quinine are known to have zinc ionophore properties i.e. they transport zinc into the cells.
As mentioned, quercetin does not principally occur in the form in which it is available as a dietary supplement (an aglycone). Instead, it occurs mostly as quercetin glycosides. Isoquercetin is one of the naturally occurring glucosides of quercetin. Isoquercetin is also sometimes called isoquercitrin, a nearly identical quercetin-3-monoglucoside. Technically the two are different (isoquercetin has a pyranose ring whereas isoquercitrin has a furanose ring), but functionally the two molecules are indistinguishable. The literature often considers them as one and uses the names interchangeably.
7. Quercetin and Other Supplements
i. Should Quercetin Be Taken With Zinc?
ii. How Zinc and Quercetin Work Together
Update: Recently, Ivermectin has come to the fore as a more effective (also long standing, cheap, generic drug), in all three stages of COVID-19. Dr Zelenko has also updated his protocols to incorporate ivermectin as an option for both the prophylactic and treatment protocols as shown below.
Best Quercetin and Zinc Supplement
b. Quercetin and Bromelain
i. Quercetin with Bromelain for Sinuses
About 35 million Americans develop sinusitis each year. This is inflammation and swelling of the tissue lining the sinuses in your nasal cavity or the areas surrounding your nose (figure below). It can be caused by infections but also nose related problems like a polyps (benign growth), blockages or allergies.
Acute sinusitis – an infection that is often triggered by the flu or cold. The flu or cold virus attacks your sinuses causing them to swell and become narrow. Your body responds by producing mucus. When the sinuses become blocked and are filled with mucus, viruses, fungi or bacteria can grow and cause infections that cause pressure and headache.
Chronic sinusitis – an infection that lasts for more than 3 weeks and can continue indefinitely if not treated. It is often caused by allergies, fungal infections or weakened immune system.
ii. Quercetin with Bromelain for Inflammation
Studies have shown that systemic enzymes for inflammation (like bromelain) combined with quercetin, produce greater anti-inflammatory benefits than either one used alone. Thus, the combination of bromelain and quercetin is ideal for effectively inhibiting the inflammatory response in both acute and chronic inflammatory conditions.
Since bromelain and quercetin are recommended to be taken together for maximum anti-inflammatory benefit, formulas that contain both ingredients are ideal. This also simplifies the dosing schedule and reduces the total number of capsules needed to be taken throughout the day.
iii. Quercetin with Bromelain for Allergies
iv. Can you take a quercetin supplement with a pineapple allergy?
If you’re allergic to pineapples, you should avoid quercetin supplements with bromelain. Bromelain, an enzyme in pineapples, is added to quercetin supplements to boost bioavailability. Overuse of bromelain can create problems for consumers.
c. Quercetin and Vitamin C
i. Covid 19 (FLCCC I-MASK+ Protocol)
d. Quercetin, Bromelain and Vitamin C
Quercetin with Bromelain and Vitamin C Supplements
e. Quercetin, Zinc, Bromelain and Vitamin C
The AAPS recommends the following outpatient treatment protocol for COVID-19:
- Quercetin oral 500 mg twice a day.
- Vitamin C 3000 mg
- Vitamin D3 5000 IU
- Zinc sulphate 220 mg
f. Quercetin and EGCG / Green Tea Extract
8. What Not To Take With Quercetin?
a. Quercetin Interactions with Antibiotics (Quinolone antibiotics)
Some of these antibiotics that might interact with quercetin include ciprofloxacin (Cipro), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).
b. Quercetin Interactions with Cyclosporin (Neoral, Sandimmune)
c. Quercetin Interactions with Drugs
i. Medications changed by the liver
Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with these medications that are changed by the liver might increase the effects and side effects of your medication. Before taking quercetin talk to your healthcare provider if you take any medications that are changed by the liver.
Some medications that are changed by the liver include paclitaxel (Taxol), rosiglitazone (Avandia), amiodarone (Cordarone), docetaxel (Taxotere), repaglinide (Prandin), verapamil (Calan, Isoptin, Verelan), celecoxib (Celebrex), diclofenac (Voltaren), fluvastatin (Lescol), glipizide (Glucotrol), ibuprofen (Advil, Motrin), irbesartan (Avapro), losartan (Cozaar), phenytoin (Dilantin), piroxicam (Feldene), tamoxifen (Nolvadex), tolbutamide (Tolinase), torsemide (Demadex), warfarin (Coumadin), amitriptyline (Elavil), codeine, flecainide (Tambocor), haloperidol (Haldol), imipramine (Tofranil), metoprolol (Lopressor, Toprol XL), ondansetron (Zofran), paroxetine (Paxil), risperidone (Risperdal), tramadol (Ultram), venlafaxine (Effexor), lovastatin (Mevacor), clarithromycin (Biaxin), cyclosporine (Neoral, Sandimmune), diltiazem (Cardizem), estrogens, indinavir (Crixivan), triazolam (Halcion), verapamil (Calan, Isoptin, Verelan), alfentanil (Alfenta), fentanyl (Sublimaze), losartan (Cozaar), fluoxetine (Prozac), midazolam (Versed), omeprazole (Prilosec), lansoprazole (Prevacid), propranolol (Inderal), fexofenadine (Allegra), amitriptyline (Elavil), amiodarone (Cordarone), citalopram (Celexa), sertraline (Zoloft), ketoconazole (Nizoral), itraconazole (Sporanox) and others.
ii. Medications moved by pumps in cells (P-glycoprotein Substrates)
Some medications are moved by pumps in cells. Quercetin might make these pumps less active and increase how much of some medications get absorbed by the body. This might cause more side effects from some medications.
Some medications that are moved by these pumps include diltiazem (Cardizem), verapamil (Calan, Isoptin, Verelan), digoxin (Lanoxin) cyclosporine (Neoral, Sandimmune), saquinavir (Invirase), amprenavir (Agenerase), nelfinavir (Viracept), loperamide (Imodium), quinidine, paclitaxel (Taxol), vincristine, etoposide (VP16, VePesid), cimetidine (Tagamet), ranitidine (Zantac), fexofenadine (Allegra), ketoconazole (Nizoral), itraconazole (Sporanox), and others.
9. Quercetin Side Effects
Any side effects tend to be mild. Quercetin side effects include tingling and numbness, headache, and nausea. Your chance of experiencing side effects increases at higher dosages (over 1,000mg).
- Blurred vision
- dull ache or feeling of pressure or heaviness in legs
- fluid accumulation in the knee
- itching skin near damaged veins
- pounding in the ears
- red or scaling skin
- slow or fast heartbeat
- swollen feet and ankles
- tingling of the arms and legs
- stomach upset
a. Who should not take a quercetin supplement?
Quercetin appears safe for anyone to take when used in normal dosages. However, there’s limited research on how quercetin supplements affect women who are pregnant or breastfeeding.
Therefore, you should talk to your doctor before taking Quercetin.
In one study, researchers gave participants 2,000mg to 5,000mg of quercetin per day with no adverse effects or signs of toxicity reported. Generally, quercetin is safe to take even in high doses, although you may experience mild side effects like nausea, digestive issues, and headaches at high doses. Excessively high doses of quercetin could lead to kidney problems.
10. Zelenko Covid-19 Prophylaxis Protocol
a. Low Risk Patients
- Zinc (Elemental Zinc) 25mg 1 time a day (PubMed) (Amazon)
- Vitamin D3 5000 iu 1 time a day (vdnmeta.com) (Amazon)
- Vitamin C 250 – 500 mg 1 time a day (PubMed) (Amazon)
- Quercetin 250 mg 1 time a day until a safe and efficacious vaccine becomes available (J. Agric. Food Chem. 2014) (Amazon)
- If Quercetin is unavailable, then use Epigallocatechin-gallate (EGCG) 200mg 1 time a day (J. Agric. Food Chem. 2014)