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Quercetin

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What Is Quercetin? Antioxidant Science, Immune Support & B2B Sourcing Guide (2026)

Meta Title: What Is Quercetin? Flavonoid Antioxidant Science & B2B Sourcing Guide (2026)Meta Description: Comprehensive guide to Quercetin extract for B2B buyers. Covers antioxidant science, immune support, bioavailability enhancement, quality specifications, and sourcing from a certified plant extract manufacturer.URL Slug: quercetinKeywords: quercetin extract, quercetin supplement, quercetin powder, flavonoid antioxidant, immune support supplement, natural quercetin source, quercetin phytosome, quercetin bulk supplier, plant extract manufacturer, Greensky Bio

Quercetin is the most abundant dietary flavonoid and one of the most extensively researched plant polyphenols in nutritional science. Found in a wide variety of fruits, vegetables, and herbs, quercetin has demonstrated powerful antioxidant, anti-inflammatory, antihistamine, and immunomodulatory properties that make it one of the most versatile botanical ingredients for B2B formulation.

For supplement manufacturers and food producers sourcing quercetin extract, understanding its diverse mechanisms of action, bioavailability challenges, and quality sourcing requirements is essential for developing effective, marketable products.

What Is Quercetin?

Quercetin (C₁₅H₁₀O₇) is a flavonoid belonging to the flavonol subclass. It is one of the most widely distributed plant flavonoids, present in thousands of edible and medicinal plants. The name derives from the Latin quercetum, meaning "oak forest," reflecting its abundance in oak bark and leaves.

Chemical Profile:

• Chemical Name: 3,3',4',5,7-Pentahydroxyflavone

• CAS Number: 117-39-5

• Molecular Weight: 302.24 g/mol

• Classification: Flavonoid, Flavonol, Polyphenol

• Common Forms: Quercetin dihydrate, Quercetin anhydrous, Quercetin phytosome, Liposomal quercetin

Quercetin vs. Quercetin Derivatives

The Science: How Quercetin Works in the Body

1. Antioxidant Powerhouse

Quercetin is one of the most potent antioxidant flavonoids available, with an ORAC (Oxygen Radical Absorbance Capacity) value significantly higher than vitamin C and vitamin E. Its antioxidant mechanisms include:

• Free radical scavenging: Direct neutralization of reactive oxygen species (ROS) including superoxide, hydroxyl, and peroxyl radicals

• Metal chelation: Binding of transition metals (iron, copper) that catalyze free radical formation

• Antioxidant enzyme upregulation: Increasing endogenous antioxidant defenses including superoxide dismutase (SOD), catalase, and glutathione peroxidase

• Nitric oxide modulation: Supporting healthy endothelial function through balanced NO production

2. Anti-Inflammatory Action

Quercetin inhibits multiple inflammatory pathways:

• NF-κB inhibition: Suppresses the master regulator of inflammatory gene expression

• COX and LOX inhibition: Reduces production of inflammatory prostaglandins and leukotrienes

• Cytokine modulation: Decreases production of TNF-α, IL-6, and IL-1β

• NLRP3 inflammasome inhibition: Blocks a key driver of chronic inflammation

3. Immune System Modulation

Quercetin's immunomodulatory properties are multi-faceted:

• Mast cell stabilization: Inhibits histamine release from mast cells, supporting natural allergy relief

• Antiviral activity: Interferes with viral replication cycles and cellular entry mechanisms

• Zinc ionophore activity: Facilitates zinc uptake into cells, supporting antiviral immune responses

• NK cell activation: Enhances natural killer cell activity for immune surveillance

4. Cardiovascular Support

Quercetin supports cardiovascular health through:

• Blood pressure regulation: Clinical trials have shown modest but significant reductions in both systolic and diastolic blood pressure

• Endothelial protection: Protects vascular endothelial cells from oxidative damage

• LDL oxidation prevention: Reduces oxidized LDL, a key factor in atherosclerosis development

• Anti-platelet activity: May help prevent excessive platelet aggregation

5. Metabolic Health

Emerging research suggests quercetin may support metabolic health:

• AMPK activation: Similar to berberine, quercetin activates AMPK, supporting glucose metabolism

• Insulin sensitivity: May improve insulin signaling pathways

• Anti-obesity effects: Some studies suggest quercetin may help regulate adipocyte function

Clinical Evidence Summary

Allergy and Immune Support

Multiple studies support quercetin's role in managing allergic responses:

• A 2016 study found quercetin significantly reduced symptoms of allergic rhinitis

• Research demonstrates quercetin's ability to inhibit histamine release from basophils and mast cells

• The zinc ionophore property gained significant attention during 2020-2022 for immune support

Cardiovascular Health

• A 2016 meta-analysis of randomized controlled trials found quercetin supplementation significantly reduced systolic BP (by 3.04 mmHg) and diastolic BP (by 2.63 mmHg)

• Higher doses (≥ 500 mg/day) showed greater blood pressure-lowering effects

• Quercetin-rich diets are associated with reduced cardiovascular disease risk

Exercise Performance and Recovery

• Some studies show quercetin may improve exercise endurance and reduce exercise-induced inflammation

• Benefits appear most pronounced in untrained individuals and during periods of intense physical stress

Natural Sources of Quercetin

Dietary Sources

Commercial Extraction Sources

For industrial-scale production, quercetin is typically extracted from:

1. Sophora japonica (Japanese Pagoda Tree) buds — Highest natural concentration, most common commercial source

2. Onion peel extract — Sustainable source from food processing waste

3. Fagopyrum esculentum (Tartary Buckwheat) — Rich in rutin, which can be converted to quercetin

The Bioavailability Challenge

Quercetin's main limitation is its relatively low oral bioavailability, estimated at less than 2% in free form. Several factors contribute to this:

• Poor water solubility — Limited dissolution in gastrointestinal fluids

• Extensive first-pass metabolism — Rapid conjugation in the liver and intestinal wall

• Efflux by P-glycoprotein — Active transport back into the gut lumen

Bioavailability Enhancement Strategies

Quality Specifications for B2B Buyers

Standard Product Specifications

Certification Requirements

• ISO 22000 — Food Safety Management

• BRCGS — Global standard for food safety

• GMP — Good Manufacturing Practice

• HALAL & Kosher — Religious dietary compliance

• USDA Organic / Ecocert — For organic-certified products

Market Trends and Demand (2026)

Key Demand Drivers

1. Immune Health Awareness: Sustained consumer interest in immune-support ingredients post-2020

2. Natural Allergy Solutions: Growing preference for natural alternatives to synthetic antihistamines

3. Anti-Aging Market: Quercetin's antioxidant properties align with healthy aging trends

4. Sports Nutrition: Increasing use in recovery and performance formulations

5. Clean Label Movement: Quercetin's natural plant origin appeals to clean-label consumers

Popular Quercetin Combinations

• Quercetin + Vitamin C: Synergistic antioxidant and immune support

• Quercetin + Bromelain: Enhanced anti-inflammatory and anti-allergy effects

• Quercetin + Zinc: Enhanced antiviral immune support (zinc ionophore effect)

• Quercetin + Resveratrol: Combined anti-aging and cardiovascular support

• Quercetin + Curcumin: Potentiated anti-inflammatory effects

Sourcing Quercetin from Greensky Bio

Hangzhou Greensky Biological Tech. Co., Ltd. offers high-purity quercetin extract sourced from premium Sophora japonica and other natural botanical sources.

Why Choose Greensky Bio for Quercetin?

• Premium botanical sourcing: Highest-quality raw materials from verified sources

• Advanced purification technology: Ensures consistent ≥ 95% and ≥ 98% purity levels

• Full certification portfolio: ISO 22000, BRCGS, GMP, HALAL, Kosher

• Independent laboratory testing: HPLC, GC, UV for comprehensive quality control

• Custom specifications: Particle size, form (dihydrate, anhydrous, phytosome), and packaging

• Global export experience: Supply to Europe, USA, South Korea, Russia, and beyond

• Competitive pricing: Direct manufacturer pricing with reliable, scalable supply

• Technical support: Expert guidance on formulation, bioavailability enhancement, and regulatory compliance

Available Product Forms

• Quercetin Dihydrate (≥ 95%, ≥ 98%)

• Quercetin Anhydrous

• Quercetin Phytosome

• Custom specifications and formulations available

Frequently Asked Questions

Q: What is the recommended daily dose of quercetin?A: Typical doses range from 500 mg to 1000 mg per day for general health support. Higher doses (1000-2000 mg/day) may be used for specific therapeutic applications under professional guidance.

Q: Is quercetin safe for long-term use?A: Quercetin has an excellent safety profile. Long-term studies at doses up to 1000 mg/day have shown no significant adverse effects. The FDA includes quercetin in its list of GRAS (Generally Recognized As Safe) substances.

Q: What is the best time to take quercetin?A: Quercetin is fat-soluble and is best absorbed when taken with meals containing some fat. Splitting the dose between morning and evening may help maintain stable blood levels.

Q: Can quercetin be combined with other supplements?A: Yes, quercetin combines well with vitamin C, bromelain, zinc, Curcumin, resveratrol, and many other botanical extracts. It is one of the most versatile supplement ingredients.

Q: What is the difference between rutin and quercetin?A: Rutin is a glycoside of quercetin (quercetin + rutinose sugar). In the body, rutin is converted to quercetin. Rutin has lower bioavailability but greater stability. Both have similar health benefits.

Conclusion

Quercetin stands as one of the most versatile and scientifically validated botanical ingredients available today. Its broad spectrum of antioxidant, anti-inflammatory, immune-modulating, and cardiovascular benefits makes it an essential ingredient for a wide range of health formulations — from immune support and allergy relief to sports nutrition and healthy aging.

For B2B buyers, Greensky Bio provides high-purity quercetin extract with comprehensive quality certifications, advanced formulation options (including phytosome technology), and competitive manufacturer-direct pricing — making it an ideal partner for supplement and food product development.

Hangzhou Greensky Biological Tech. Co., Ltd. — Your trusted source for premium quercetin and natural plant extracts. Contact us for specifications, samples, and pricing.