Quercetin
A potent plant flavonoid with anti-inflammatory, antihistamine, and immune-modulating properties.
Also known as: Quercetin Dihydrate • Quercetin Phytosome
Overview
Quercetin is one of the most abundant flavonoids in the human diet, found in onions, apples, berries, and tea. It has gained significant attention for its broad-spectrum health benefits, including powerful antioxidant and anti-inflammatory effects, natural antihistamine properties, immune modulation, and cardiovascular support. Quercetin also acts as a zinc ionophore — helping zinc enter cells — which has implications for immune defense.
Key Benefits
Natural Antihistamine
Quercetin stabilizes mast cells and inhibits histamine release, making it a natural alternative for seasonal allergy relief. Studies show it reduces allergy symptoms including sneezing, itching, and nasal congestion.
Anti-Inflammatory
Quercetin inhibits NF-κB, COX-2, and lipoxygenase pathways — key drivers of chronic inflammation. It reduces inflammatory markers including CRP, IL-6, and TNF-alpha.
Zinc Ionophore
Quercetin acts as a zinc ionophore, facilitating zinc transport across cell membranes. This enhances zinc's intracellular antiviral activity, which is why quercetin and zinc are often taken together for immune support.
Cardiovascular Support
Meta-analyses show quercetin supplementation reduces systolic blood pressure by 3–7 mmHg and improves endothelial function. It also reduces LDL oxidation, a key step in atherosclerosis.
Dosage & How to Take
Standard supplemental dose is 500–1,000mg daily, typically divided into two doses.
| Purpose | Dose | Notes |
|---|---|---|
| General health | 500 mg/day | With a fat-containing meal |
| Allergy relief | 500–1,000 mg/day | Start 4–6 weeks before allergy season |
| Immune support | 500–1,000 mg/day | Often combined with zinc and vitamin C |
| Cardiovascular | 500–750 mg/day | Consistent daily use for blood pressure benefits |
Best Time to Take
With meals for better absorption; divide into 2 daily doses
With or Without Food
Yes — fat-containing meals significantly improve absorption
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| Quercetin Phytosome (Quercefit) | Excellent (20x standard) | Maximum absorption | Complexed with sunflower lecithin; dramatically improved bioavailability |
| Isoquercetin | Good (5x standard quercetin) | Good balance of cost and absorption | Glycoside form with better water solubility |
| Quercetin Dihydrate | Poor | Budget option | Standard form; poorly absorbed without enhancement |
| EMIQ (Enzymatically Modified Isoquercitrin) | Very Good | Allergy relief | Water-soluble form with enhanced absorption |
Side Effects & Safety
Common
- Headache (rare)
- Mild GI discomfort
Rare
- Tingling in extremities at very high doses
- Kidney damage at extreme doses (>3g/day)
Contraindications
- Pregnancy (insufficient safety data at supplemental doses)
- Kidney disease (high doses)
Interactions
Quercetin may increase cyclosporine blood levels
May enhance anticoagulant effects
Quercetin enhances zinc's intracellular activity — beneficial combination
Scientific Research
Quercetin and Allergies
Quercetin significantly reduced allergy symptoms and improved quality of life in seasonal allergy sufferers
Quercetin and Blood Pressure
Meta-analysis: quercetin reduced systolic BP by 3.04 mmHg and diastolic BP by 2.63 mmHg
Quercetin Phytosome Bioavailability
Quercetin Phytosome achieved 20x higher plasma levels than standard quercetin
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.