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Quercetin

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

1. What Is Quercetin and Why Is It the Most Abundant Dietary Flavonoid?

Quercetin (3,3',4',5,7-pentahydroxyflavone) is a flavonol — a subclass of flavonoid polyphenols — found abundantly in fruits, vegetables, grains, and beverages. First isolated in 1857, quercetin is the most prevalent flavonoid in the human diet, with average daily intake estimated at 10–100mg in Western populations.

In 2026, the global quercetin market is valued at over $200 million and growing rapidly, driven by demand for immune support supplements, anti-inflammatory formulations, sports recovery products, and natural antihistamine alternatives. For B2B buyers and product formulators, understanding quercetin's science, bioavailability challenges, and quality sourcing is essential for developing effective products.

2. Natural Sources and Commercial Extraction

Quercetin is widely distributed in the plant kingdom. The most significant commercial sources include:

Commercial quercetin is typically produced by enzymatic or acid hydrolysis of rutin (quercetin-3-rutinoside) extracted from Sophora japonica buds. The resulting quercetin dihydrate offers high purity (≥95%) and excellent stability for supplement manufacturing.

3. Key Biological Mechanisms

3.1 Antioxidant Activity

Quercetin is one of the most potent dietary antioxidants, with an ORAC value significantly higher than vitamin C. Its mechanisms include:

• Free radical scavenging: Direct neutralization of ROS (reactive oxygen species) via phenolic hydroxyl groups

• Metal chelation: Binding of iron and copper ions to prevent Fenton reaction-driven oxidative damage

• Antioxidant enzyme upregulation: Enhancement of superoxide dismutase (SOD), catalase, and glutathione peroxidase activity

3.2 Anti-Inflammatory Effects

Quercetin inhibits multiple inflammatory pathways:

• NF-κB pathway suppression: Reduces production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β)

• COX-2 and LOX inhibition: Modulates prostaglandin and leukotriene synthesis

• Mast cell stabilization: Reduces histamine release, supporting natural allergy relief

3.3 Immune Modulation

Research demonstrates quercetin's ability to:

• Enhance natural killer (NK) cell activity

• Modulate T-cell differentiation toward regulatory phenotypes

• Support barrier function in respiratory and gastrointestinal epithelium

• Exhibit antiviral properties against multiple viral strains through zinc ionophore activity

4. Clinical Evidence and Health Applications

4.1 Immune and Respiratory Health

• A 2020 study in Nutrients found that quercetin supplementation (500–1000mg/day) significantly reduced upper respiratory tract infection (URTI) incidence and severity in trained athletes

• Research in the Journal of Allergy and Clinical Immunology supports quercetin's role in managing seasonal allergic rhinitis through mast cell stabilization

4.2 Cardiovascular Health

• Meta-analyses indicate quercetin supplementation modestly reduces blood pressure (3–5 mmHg) in hypertensive individuals

• Improves endothelial function and reduces oxidized LDL cholesterol

• May support healthy arterial stiffness markers

4.3 Exercise Performance and Recovery

• Studies show quercetin may improve endurance capacity and reduce exercise-induced inflammation

• Combined with resveratrol and creatine, quercetin enhanced mitochondrial biogenesis in training studies

• Post-exercise supplementation reduces DOMS (delayed onset muscle soreness) markers

5. Bioavailability and Formulation Strategies

Quercetin aglycone has limited oral bioavailability (~2%–20%) due to poor water solubility and extensive first-pass metabolism. Advanced delivery technologies include:

6. Recommended Dosage by Application

7. Quality Sourcing Checklist for B2B Buyers

1. Purity: ≥95% quercetin dihydrate (HPLC verified)

2. Rutin Content: Residual rutin < 3% (if producing from rutin hydrolysis)

3. Heavy Metals: Pb < 1ppm, As < 1ppm, Cd < 0.5ppm, Hg < 0.1ppm

4. Solvent Residue: Ethanol/methanol within ICH Q3C limits

5. Microbial Limits: Total plate count < 10,000 CFU/g

6. Particle Size: D90 < 150μm for optimal dissolution

7. Certifications: ISO22000, GMP, HALAL, Kosher for global market compliance

8. Market Trends and Opportunities (2026)

• Zinc ionophore formulations combining quercetin with zinc for immune support

• Gummy and chewable formats using nanoemulsified quercetin for consumer-friendly delivery

• Pet health supplements targeting inflammation and immune support

• Functional beverages with stabilized quercetin formulations

9. Why Choose Greensky for Quercetin Extract

Hangzhou Greensky Biological Tech. Co., Ltd. brings over two decades of plant extract manufacturing excellence to quercetin production:

• High-purity quercetin dihydrate (≥95% by HPLC) from sustainable Sophora japonica sources

• Custom specifications available: 85%, 95%, 98% purity grades

• Comprehensive analytical documentation: COA, HPLC reports, heavy metal screening, microbial testing

• GMP-compliant production with ISO22000, BRCGS, and Ecocert certifications

• Advanced in-house laboratory with HPLC, GC, and UV for quality verification

With established export markets across Europe, the United States, South Korea, and Russia, Greensky is your reliable B2B quercetin extract supplier.

Contact Greensky for competitive pricing, samples, and technical specifications for your quercetin sourcing needs.