What is Quercetin?
Quercetin is a plant compound that has been shown to help alleviate unpleasant seasonal side effects like allergy symptoms. Learn more about this powerful antioxidant here.
Properties of Quercetin
This antioxidant is a secondary plant compound that belongs to the group of flavonols, a group of bioflavonoids. The antioxidant may be helpful for minimizing symptoms of multiple diseases, such as high blood pressure and seasonal allergies. Quercetin may also help strengthen the immune system.
However, quercetin cannot be produced by our body itself.
In nature, the antioxidant properties of quercetin serve to protect against harmful environmental conditions such as predators, damage caused by UV radiation and other external influences.
The yellow colored antioxidant is widely distributed in the plant kingdom. Quercetin is found in many fruits and vegetables, and is responsible for the bright colors in plants.
Quercetin From Natural Sources
Among the most commonly used foods, onions asparagus, apples, blueberries, figs, kale, and cocoa have particularly high amounts of the antioxidant .
The amount of the substance in foods varies depending on when they are harvested, grown, and fresh.
The content in foods can also be lost depending on how they are prepared.
Foods High in Quercetin
- Apples with peel (3.6mg/kg)
- Beans (4mg/100g)
- Watercress (30mg/100g)
- Coriander leaves (over 40mg/100g)
- Sorrel (over 80mg/100g)
High quercetin content in apples
The most quercetin rich foods are those with an outer peel, such as the red peel of an apple.
When you remove the peel of an apple, it has practically no quercetin conent left. In addition, long storage of fruit or vegetables also has a negative effect on the content.
Due to poor bioavailability, our bodies absorb a very small amount of this plant substance from food (5.3%).
Quercetin levels in food are also affected by heating, added fat, and freshness of foods.
The amount in food varies even among similar foods because method of cultivation has a tremendous impact on the content of the substance.
Therefore, no one knows exactly how much of this antioxidant is really present in food or how much our body absorbed. Moreover, most people do not eat enough fruits and vegetables to guarantee sufficient levels of the antioxidant in their bodies.
Researchers estimate that 10 to 60 times the average fruits and vegetables intake is required to achieve effects seen in studies of supplementation. To obtain a quercetin dosage of just 250mg from food (without considering absorption rate) one would have to consume 7 kg of apples or 2kg of onions alone. Even after consumption of quercetin containing food items, researchers have been unable to identify how much of the substance is intact and efficiently absorbed in the body.
Quercetin health Benefits
1. Free radical scavenger
Quercetin is one of the most important antioxidants in our diet. Quercetin is used for the scavenging of free radicals in the body. These free radicals are particles that cause oxidative stress, inflammation, and cell death .
This antioxidant substance also has multiple effects on different signaling pathways in the body that can either activate or inhibit inflammatory markers. In addition, the substance can increase the synthesis of glutathione (the body's most potent antioxidant) and antioxidant enzymes . When the body can adequately utilize large amounts of the substance, the body may be additionally protected from inflammation and cell death.
2. Quercetin and Allergies
Quercetin may reduce the release of substances responsible for allergic reactions. Specifically, it may reduce histamine release. Histamine is the molecule that triggers the symptoms of allergies, such as stuffy nose or a cough. Thus, reducing the amount of this molecule can reduce the allergic reaction itself .
Quercetin as a natural antihistamine may help to reduce allergy symptoms.
A Japanese study showed that quercetin ingestion significantly inhibited histamine release. The effect of quercetin supplementation was almost twice as beneficial as other conventional drugs for hay fever at the same concentration .
This antioxidant may be helpful as a natural remedy for hay fever, and also for food allergies.
Animal studies show that a high dose of quercetin helped significantly lower histamine levels in rats allergic to peanuts. There were no adverse side effects related to the lungs, blood pressure, or blood vessels .
Want to learn more? Take a look at our blog article about allergies.
3. Quercetin and rheumatoid arthritis
Rheumatoid arthritis is a disease of the joints, and is frequently associated with inflammation and pain.
Quercetin has both anti-inflammatory and pain-relieving effects. There are several mechanisms responsible for this effect such as regulation and inhibition of different pathways that cause inflammation. One of these is the inhibition of inflammatory markers called cytokines.
The mechanisms responsible for the pain releaving effects of quercetin are not yet fully known. However, it is likely that this is also due to the antioxidant and anti-inflammatory effects of quercetin .
One study showed significant efficacy of the compound against inflammation and pain in rheumatoid arthritis.
After administration of quercetin to a group of women suffering from rheumatoid arthritis, researchers found significant improvements. These improvements were in morning stiffness, pain, joint tenderness, and physical function. Also in this study, quercetin reduced levels of the important inflammatory mediator for rheumatoid arthritis, TNF-alpha .
4. Quercetin and Brain Health
Recent research suggests that quercetin and mood may be related, specifically with anxiety relieving and antidepressant effects.
In mice, quercetin supplementation was able to reduce a molecule in the brain commonly associated with anxiety and depression. This molecule is called CRF (corticotropin releasing factor).
Some researchers believe that the substance's anxiety relieving and antidepressant effects are due to the reduction of CRF .
In an experiment with rats, researchers found that the antioxidant can improve cognition and contribute to anxiety relieving effects .
Recent studies also suggest that the substance may reduce the risk of Alzheimer's disease and other neurodegenerative diseases. Thus, quercetin also has an effect on brain health.
Not all mechanisms of action are completely clear, but researchers believe that the effects are due to strong antioxidant and anti-inflammatory properties .
5. Quercetin and blood pressure
Quercetin may reduce hypertension through several mechanisms of action. One mechanism is a reduction in oxidative stress and inflammatory properties. In addition, this substance may have a positive effect on blood vessel elasticity. This is done through an improvement in vasodilation controlled by endothelial cells (innermost cell layer of blood vessels).
Not all mechanisms of the relationship between quercetin and blood pressure are fully understood yet. However, according to some research studies, supplementation can make a valuable contribution to blood pressure control .
In particular, supplementation of the antioxidant has been shown to significantly reduce systolic and diastolic blood pressure. The most beneficial results were obtained with a dose of quercetin of 500 mg per day .
The advantage is that the substance only significantly lowers blood pressure in people with high blood pressure. So people with healthy blood pressure do not have to worry about a sudden drop in levels.
In addition to the benefits on blood pressure, the substance may also have a positive effect on other health factors, such as decreasing cholesterol and triglyceride levels .
6. Quercetin and competitive sports
The antioxidant is also of interest to athletes.
A team of researchers at the University of South Carolina in Columbia (USA) conducted a study with twelve subjects. Each subject consumed 500 mg of the substance twice a day for one week. The subjects were able to improve maximum oxygen intake by 3.9 percent. In addition, the subjects extend the so-called "time to exhaustion" by 13.2 percent as a result of taking the antioxidant .
Quercetin and the thyroid gland
In experiments with mice, quercetin (as well as other important antioxidants) significantly inhibits the enzyme deiodinase. This enzyme converts the hormone T4 into the active thyroid hormone T3. Impairment of this enzymes can result in hypothyroidism. Because of these negative effects, quercetin should not be consumed in excess above the recommended daily dosage.
Anyone who wants to take this plant substance but has impaired thyroid function should talk to their doctor beforehand. Thyroid levels should be monitored consistently while taking the substance if there is a risk of hypothyroidism.
External supplementation is usually required for this antioxidant to exert significant effects .
An increase in blood quercetin levels can be seen at a daily dose of 150mg and above.
There are no adverse side effects at low doses of supplementation.  Quercetin side effects of thyroid function may be present at extremely high dosages. Please consult your doctor and follow the recommended daily dosage.
Low bioavailability in pills and powders
Studies have shown that pills or powders containing quercetin have very low rate of absorption at 5.3% .
So if you want to increase the amount of this antioxidant in your body, liposomal formulations with higher bioavailability are recommended.
The Solution: Liposomal Quercetin
The best supplemental form of quercetin. Liposomal encapsulation is the best way to get the antioxidant where it belongs: in our bloodstream. When liposomes are ingested, they do not enter the liver where they could be broken down. Instead, the enclosed active ingredients reach their site of action directly .
Thanks to liposomal technology, the active ingredient is protected from harmful enzymes and gastric acid of the digestive tract.
Liposomal technology ensures almost complete absorption of the active ingredient.
Interested in learning more? Take a look at our blog article about Antioxidants.
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24. Hyeongmin Kim, Yeongseok Kim, Jaehwi Lee, Liposomal formulations for enhanced lymphatic drug delivery,Asian Journal of Pharmaceutical Sciences, Volume 8, Issue 2, 2013, Pages 96-103, ISSN 1818-0876, https://doi.org/10.1016/j.ajps.2013.07.012.