Quercetin, a flavonoid found in various plants, is often discussed in nutritional and herbal contexts for its potential health benefits. What is quercetin used for? This compound is noted for its antioxidant and anti-inflammatory properties, which may support overall well-being. Quercetin has been associated with various health benefits, including immune system support and heart health. Its potential to neutralize free radicals and modulate inflammatory responses has made it a popular choice in natural wellness approaches. As a component of plant-based nutrition and herbal practices, quercetin continues to interest those exploring holistic health and wellness.
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Origin and Dietary Sources of Quercetin
Quercetin is a yellow flavonoid that can be found in many plant-based foods. Examples of natural dietary sources of quercetin include apples, onions, berries, citrus fruits, grapes, tomatoes, broccoli, and cabbage. Small amounts have also been isolated from botanical herbs, including Ginkgo biloba, St. John's wort, milk thistle, and elderberry. Quercetin is recognized for its antioxidant and anti-inflammatory properties. Consuming a diverse range of fruits and vegetables may help ensure a steady intake of quercetin, which plays a role in supporting overall health. In standard Western diets, daily intakes of quercetin through diet have been estimated between 3-40 mg. In people with high fruit and vegetable consumption, daily quercetin intake can be as high as 250 mg. (24, 33)
How Does Quercetin Work in the Body?
Quercetin is a naturally occurring flavonol, one of the six subsets of flavonoids. Flavonoids are phytochemical compounds found naturally in fruits, vegetables, herbs, nuts, and seeds with various properties, including antioxidant and anti-inflammatory effects.
Quercetin's molecular structure (pictured below) consists of 15 carbon atoms arranged in a specific arrangement of rings. A phenolic hydroxyl group and double bonds in its chemical structure allow quercetin to have antioxidant activity. Quercetin is available in various forms, including quercetin aglycone (free quercetin), quercetin glycosides, and quercetin derivatives. These forms differ in their bioavailability and absorption rates due to their chemical structures. Quercetin aglycone is the pure, unbound form of quercetin. Quercetin glycosides, on the other hand, are quercetin molecules bound to sugar molecules. Overall, quercetin is considered to have low bioavailability. Supplemental quercetin is often modified into one of its derivatives or formulated with dietary fat to improve absorption. (16, 24, 33)
Potential Benefits of Quercetin
Research has explored the potential benefits of quercetin in various areas. This article will discuss how quercetin may support the management of inflammation, allergies, cardiovascular health, immune function, and oxidative stress.
1. Anti-Inflammatory Potential of Quercetin
It is suggested that quercetin may influence the activity of certain enzymes, which could help manage inflammatory responses (16, 33). Animal studies also indicate that quercetin may affect gene expression related to inflammation.
Some studies suggest that quercetin may help reduce inflammation. Subgroup analyses indicate that quercetin might influence inflammatory markers in certain conditions, such as rheumatoid arthritis, diabetes, and metabolic syndrome.
An 8-week trial that included 50 women with rheumatoid arthritis observed that participants taking 500 mg of quercetin daily reported changes in joint stiffness and pain. Inflammatory markers were also noted to change in the quercetin group compared to placebo.
The potential anti-inflammatory effects of quercetin may also contribute to observed improvements in men with chronic pelvic pain syndrome.
2. Quercetin and Allergy Management
Quercetin is often included in formulations aimed at managing allergy symptoms. Some evidence suggests that quercetin may influence the activity of cells involved in allergic responses. Studies indicate that quercetin might affect the release of certain immune proteins involved in allergic reactions. (19)
The immune system operates through a balance between two types of helper T cells, known as Th1 and Th2 cells. These cells play roles in regulating the immune response. In allergic conditions, the balance between Th1 and Th2 cells may shift. Quercetin may help support the balance of these cells. (13)
Studies suggest that quercetin may help manage symptoms of allergic conditions, including allergic asthma, allergic rhinitis, and atopic dermatitis (13). For example, in a study of Japanese adults with allergic rhinitis, participants taking 100 mg of quercetin twice daily for one month reported improvements in symptoms.
3. Quercetin and Cardiovascular Health
Research suggests quercetin may support heart health by influencing factors related to cardiovascular function, such as blood pressure and blood sugar levels (29).
Endothelial dysfunction describes a state that occurs when the cells lining blood vessels don't function properly, which can affect blood flow and pressure. Studies on quercetin's effects on endothelial function have shown promising results, including potential improvements in blood vessel function and oxidative stress markers (2, 7, 18).
Quercetin supplementation has been associated with modest effects on blood pressure. A 2016 meta-analysis suggested that quercetin supplementation might influence blood pressure levels. The most notable changes were observed in participants taking at least 500 mg of quercetin daily.
Studies have also explored quercetin's effects on other cardiovascular health parameters. Elevated levels of C-reactive protein (CRP) are associated with cardiovascular risk; quercetin, especially at higher doses, may influence CRP levels. In a study involving patients with polycystic ovary syndrome (PCOS), those taking 1 gram of quercetin daily reported changes in blood sugar and insulin levels compared to placebo at the end of the 12-week trial.
4. Quercetin and Immune Support
Studies have explored quercetin's potential effects on immune function, including its influence on certain bacteria and viruses. Quercetin has been studied for its potential to affect bacterial cell walls and protein synthesis. (33)
Additionally, research has investigated quercetin's potential role in managing viral infections by affecting viral replication. Quercetin has been studied for its activity against various viruses. (5)
Studies have also explored quercetin as a potential adjunctive approach in managing fungal infections (33).
5. Antioxidant Properties of Quercetin
Quercetin is recognized for its antioxidant properties, which may help manage oxidative stress. Oxidative stress occurs when there is an imbalance between free radicals and the body's ability to neutralize them. This imbalance can lead to cellular damage. Quercetin acts as an antioxidant by scavenging free radicals, potentially supporting cellular health and overall well-being. (29)
Clinical trials have explored the antioxidant potential of quercetin. These studies have investigated its ability to influence oxidative markers and support the activity of other antioxidants in the body. (8, 16, 21)
Potential Side Effects of Quercetin and Considerations
While quercetin is considered safe when consumed in moderate amounts through dietary sources like fruits and vegetables, there are some precautions to consider when using it as a dietary supplement. Higher doses of quercetin supplements may cause headaches and upset stomach. Additionally, individuals with kidney disorders should exercise caution, as high doses have been reported to affect kidney function. There is limited data regarding the safety of quercetin administered in doses higher than 1,000 mg for longer than 12 weeks. (1, 23)
Quercetin supplements may also interact with certain medications. Therefore, individuals should consult healthcare experts before starting quercetin supplementation, especially if they are taking any of the following medications (23) :
- Antibiotics
- Blood thinners
- Chemotherapy agents
- Corticosteroids
- Cyclosporine
- Digoxin
Healthcare professionals can provide personalized recommendations regarding the appropriate dosage and ensure the safe incorporation of quercetin supplements into one's routine. Adhering to recommended dosages and seeking professional guidance ensures the safe and effective utilization of quercetin for its potential health benefits.
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Summary
Exploring the potential benefits of quercetin reveals its role in supporting overall well-being. This natural flavonoid, found in fruits and vegetables, is noted for its antioxidant, immune-supporting, and anti-inflammatory properties. Its potential to manage oxidative stress, influence immune responses, and support cardiovascular function highlights its importance in maintaining health. Quercetin offers a natural approach to supporting the immune system and promoting cellular health.
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