Quercetin is a bioflavonoid with a number of health benefits including antioxidant, anti-inflammatory, and immune-supporting properties . It is also used to improve energy levels and to reduce stress and goes well with other health-promoting supplements.  
At a Quick Glance
Also Known As
3, 3′, 4′, 5, 7-pentahydroxyflvanone
3, 3′, 4′, 5, 7-pentahydroxy-2-phenylchromen-4-one
How it Works
Is Used For
Supporting a healthy circulatory system
Promoting health and vitality
Boosting energy levels
Benefits and Effects on Humans
Based on Available Scientific Research and Anecdotal Evidence
|Supporting a Healthy Circulatory System||★★★★★|
How to Use
Recommended Serving Size
The recommended Quercetin serving size is set between 150 – 500mg daily. Do not exceed the recommended serving instructions. Quercetin can be taken in a capsule form, dissolved in water or juice, or taken sublingually (under the tongue).
- Measure the correct serving size of Icariin with a measuring scoop or scale.
- Pour this onto a credit card, spoon, or piece of paper.
- Toss the powder into the back of your mouth.
- Wash it down with a glass of water.
Quercetin breakfast smoothie:
- Measure the correct serving size of Quercetin with a measuring scoop or scale.
- Cut up 3-4 servings of your favourite fruits – bananas, apples, berries, dates, or oranges.
- Add Quercetin and fruit into a blender.
- Add 1 glass of water or fruit juice.
- Blend until smooth and drinkable.
- Enjoy as a healthy breakfast smoothie.
Quercetin is a naturally occurring plant pigment or flavonoid that is found in many foods including citrus fruits and vegetables, olive oil, and red wine. In addition, it is probably the most studied flavanol. It is found alongside Rutin in most fruits and vegetables and is especially high in concentration in onions, grapes, red wine, and chocolate. Overall, Quercetin is one of the best-studied bioflavonoids known to man. It helps reduce histamine-mediated inflammation while supporting a healthy circulatory system, boosting energy levels, and reducing stress. .
The primary benefit of Quercetin is its antioxidant effects, which help destroy harmful free radicals in the body, but it is also well-known for its anti-inflammatory and immunomodulating properties. 
Other benefits include support of respiratory health (by acting as an antihistamine), enhanced cardiovascular health, the stabilization of normal blood pressure, the reduction of cortisol levels, energy-boosting properties, and the promotion of overall good health.Quercetin is often sold online as a stack containing a Quercetin bromelain complex. Bromelain is a protease found in pineapple that has anti-inflammatory properties. 
A recent review looked into Quercetin’s benefits for the body and found it to be a highly effective supplement for promoting good health. More specifically, researchers indicated that its most important health-promoting properties related to its antioxidant effects in terms of free-radical scavenging and protecting the body against oxidative stress.  However, the same review also pointed to Quercetin’s ability to promote a healthy cardiovascular system and to improve mental focus. It may also have a role to play in regulating allergic response in some people.  
The recommended serving size for Quercetin is between 75 – 250 mg, taken once or twice per day. It can be dissolved in water, taken in capsule form, or washed down as a powder with a glass of water. Side effects are mild and rarely reported, but may include: headaches, nausea, and tingling sensations.
Do not exceed the recommended serving size. Quercetin may interact with a number of prescription medications and has not been studied sufficiently in pregnant and breastfeeding women. Please consult your physician if you are using medication or have any underlying medical conditions.
Bioflavonoids are a type of plant compound with numerous health benefits in the human body. They have been used for thousands of years in traditional medicine, although they may not have been called ‘bioflavonoids’ at the time. Of all the bioflavonoid compounds known to man, Quercetin has arguably been studied the most. Today, bioflavonoids are used for a number of reasons including supporting the immune-enhancing benefits of Vitamin C, strengthening the circulatory system by improving blood circulation, and acting as natural antioxidants and anti-inflammatory compounds.
In a 2015 study, researchers explored the associations between flavonoid intake and mortality in a group of over 1000 women over the age of 75 for a 5-year period. The research showed that the participants with a higher flavonoid intake had a lower risk of all-cause mortality and experienced significant benefits for cardiovascular health. It is important to note that this study used food intake and diet as a measure of flavonoid consumption. We do not suggest that Quercetin supplements reduce the risk of mortality, but we point out the clear positive effects on health that flavonoids confer.
There are also some interesting studies from around the world about the secondary benefits of bioflavonoids. As an example, researchers in Switzerland have explored the use of bioflavonoids in plants as a protective measure against radiation. Furthermore, researchers from France have found an inverse relationship between dietary flavonoid intake and the occurrence of dementia and Alzheimer’s disease in older adults (i.e., the more flavonoids consumed, the lower the risk of dementia). Finally, research has also indicated that there may be a potential for flavonoids to be used as antimicrobial agents against bacteria and fungi in the near future.
3. Quercetin Glycosides
Quercetin is sometimes found in glycoside form. This means that the compound is bound to one or more sugar molecules. Glycoside forms may alter the absorption and metabolism of a supplement. The most important Quercetin glycosides include:
- Quercetin-3-O-Rutinoside (Rutin): A naturally-occurring glycoside found in a variety of plant species, consisting of Quercetin bound to rutinose.
- Quercetin-3-O-Rhamnoside: Quercetin bound to rhamnose. Also found in some plant species.
- Quercetin-3-Glucoside (Isoquercetin): A Quercetin compound bound to a simple glucose molecule on the 3’ carbon. Often found in food products.
- Quercetin 3-O-β-D-glucoside: Similar to Isoquercetin, but with some chemical modifications.
- Quercetin-4′-O-Glucoside (Spiraeoside): Similar to Isoquercetin, but with the glucose sugar bound to the 4’ carbon. Found in some herb species as well as in onions.
- Quercetin 3-D-galactoside (Hyperin): Quercetin bound to a galactose sugar.
- Quercetin-3,6-Malonylglucoside (Q3MG): Quercetin bound to glucose with an additional malonyl group. Found in some plant and herb species.
- Quercetin-3-O-robinobioside: Quercetin bound to a robinose sugar group.
- Quercetin Rhamnohexoside: Quercetin bound to rhamnohexodise, found in several plant species.
4. Human Effects
4.1. Supports a Healthy Circulatory System
One major benefit of Quercetin is its ability to support a healthy circulatory system. A large body of research indicates that Quercetin may be able to support a healthy circulatory system by enhancing blood flow as well as protecting against low-density lipoprotein (LDL) oxidation. A recent meta-analysis called Quercetin’s effects on lipid levels into question, but found significant benefits on triglyceride levels at servings greater than 50 mg/day. LDL (bad cholesterol) and triglycerides (fats) are responsible for many major forms of cardiovascular disease, and the oxidation of LDLs in arteries can have negative health effects over long periods of time.
“The metabolites of Quercetin show partial protective effects on endothelial function and LDL oxidation. Quercetin produces undisputed antihypertensive and antiatherogenic effects, prevents endothelial dysfunction and protects the myocardium from ischemic damage.” (Perez-Vizcaino F, Duarte J., 2010) 
Furthermore, research has indicated that Quercetin may be able to help moderately increase high-density lipoprotein (HDL) cholesterol levels (good cholesterol). In the body, HDL-cholesterol is used to transport excess cholesterol back to the liver, where it is metabolized into bile. This is called the ‘reverse cholesterol transport system’. It for is this reason that HDL-cholesterol is considered the ‘good’ form of cholesterol, as it is actually involved in removing cholesterol from the blood. For most people, an increase in the ratio of HDL- to LDL-cholesterol is important for maintaining good health.
4.2. Powerful Anti-Inflammatory Benefits
Another one of Quercetin’s major benefits is that it works as a natural anti-inflammatory compound. Histamine is produced by the body’s immune system in response to allergic substances such as pollen, dust, animal hair, and air-borne bacteria. It results in the typical cold-like symptoms or hay fever (i.e., red, swollen eyes, puffy cheeks, and a runny nose). Quercetin supplementation has demonstrated the ability to reduce markers of inflammation as well as redness and skin photosensitivity:
“…flavonoids are potent anti-oxidant and anti-inflammatory compounds with mast cell inhibitory actions. Here, we first compared the flavonoid Quercetin (Que) and cromolyn on cultured human mast cells. Que and cromolyn (100 µM) can effectively inhibit secretion of histamine and PGD.” (Weng et al., 2012)
In 2016, researchers published a new study regarding the examination of Quercetin’s effects on inflammation. In their literary review, the researchers found several benefits relating to Quercetin’s use as a strong anti-inflammatory agent.  Anti-inflammatory supplements are highly useful in promoting good health. Ill-health often develops due to chronic inflammation and thusly, taking an anti-inflammatory supplement is a great way to reduce this symptom and avoid having to use chemical-based pharmaceuticals, which often cause unwanted side effects.
4.3. Helps to Reduce Stress
Cortisol is commonly known as the ‘stress-hormone’ and it is secreted in response to stress, which triggers changes in the body including increased blood pressure and heart rate. High-stress levels can also cause headaches, tiredness and a general feeling of negativity. Quercetin supplementation at large servings has been found to inhibit the expression of a critical gene involved in the synthesis of cortisol.  This may be a part of the mechanism behind Quercetin’s anti-stress properties. Less stress generally means a better feeling of good health, improved sleep, and an enhanced quality of life.
To benefit fully from Quercetin’s anti-stress effects, we recommend using this supplement in addition to a healthy diet and regular exercise. The effects of exercise on stress cannot be overstated. Unfortunately, there is no magic product that can completely destroy stress. However, eating healthy foods, getting regular exercise, and using natural supplements with verified benefits on stress is about as good of a start as you can have!
4.4. Supports a Healthy Metabolism and Boosts Energy Levels
Studies have indicated that Quercetin may be able to promote a healthy metabolism and help support optimal energy production in the body. In 2009, a 6-week double-blind placebo study involving 93 overweight and obese adults found that supplementation with Quercetin resulted in lowered systolic blood pressure as well as total cholesterol serum levels for the entire group.
This study also correlated with previous findings that Quercetin is able to lower serum LDL levels by preventing LDL oxidation, which reflects antioxidant effects. This is especially relevant in countries where there is a large problem with obesity and high cholesterol levels. According to the Centre for Disease Control (CDC) in the US, up to 71 million adults in the Americans (33,5%) have high levels of LDL.
There has been a lot of debate in scientific circles regarding whether or not Quercetin is able to boost energy levels and increase performance on its own. In 2009, a study was conducted at the University of South Carolina involving 12 healthy subjects, where half were given Quercetin and the other half received a placebo. The results indicated that the Quercetin supplements helped boost both endurance and VO2 max levels significantly.  Participants were given daily servings of Quercetin (500 mg) over seven days and endurance and VO2 max levels were monitored.
“The results: After taking quercetin for only seven days, the participants had a 13.2 percent increase in endurance and a 3.9 percent increase in VO2max.” (M Davis et al., 2009) 
4.5. Helps to Support a Healthy Immune System
Quercetin is well-known for its benefits on the immune system. Researchers around the world have been engaged in this topic for decades, and there is a plethora of information supporting Quercetin’s immune benefit claims. For example, researchers in 2017 pointed out the immunostimulatory benefits of Quercetin in mice by measuring serum IG antibodies.
In a more recent study, dating to 2019, researchers indicated that Quercetin and other flavonoids may help to support the immune system by regulating the Th1/Th2 balance of T-helper cells and by reducing the activity of pro-inflammatory cytokines.
In a similar animal study, researchers indicated that Quercetin had the potential to reduce the hyperresponsiveness of the airway patients. This is quite an exciting possibility, but needs to be further researched before we can fully understand its significance.
Interestingly, research has indicated that Quercetin acts as an ionophore for zinc – helping to catalyze ion transport over cell membranes. Through its actions as an ionophore, Quercetin works with zinc to help quell the multiplication of a variety of types of viruses in the human body.
5. Safety and Toxicity
5.1. Side Effects
Quercetin is generally considered as safe at normal servings of around 150 – 500 mg per day. Side effects of large doses can include headaches, nausea, and a tingling sensation in the arms and legs.
In 2017, a review paper found that, in studies using servings of up to 1000 mg per day, participants rarely reported adverse effects and, if they did, they tended to be mild in nature. However, the researchers did point out that some damage to organs and drug-interactions was found in animal studies that involved the use of very large servings of Quercetin. Although the concentrations used in these studies would be practically very difficult to achieve through oral Quercetin supplementation, it is still not recommended to exceed the serving size.
In 2009, a clinical study found that after 6 weeks of daily Quercetin supplementation at a serving of 150 mg, liver and kidney function were completely unaffected and neither were haematology or serum electrolyte levels, indicating that regular medium level dosage is safe for long term use.
Currently, there is no sufficient research indicating Quercetin’s safety for pregnant or breastfeeding women. Quercetin may interact with a number of prescription medications. Please consult your physician if you are taking any medication, or have any underlying medical conditions.
Content Updated On: July 1st, 2020References
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