Quercetin is a flavonoid belonging to the flavonol subfamily, one of the most common and best-studied polyphenols in the plant diet. Its two distinctive properties— inhibition of mast cell degranulation (allergy relief) and activation of the Nrf2 pathway (antioxidant)—make it a unique active ingredient in its category. Explore our line of natural antioxidants.
What is quercetin?
Quercetin (C₁₅H₁₀O₇) is a flavonol found throughout the plant kingdom—in onions, apples, capers, and berries. Its polyphenolic structure gives it a powerful ability to chelate metals and neutralize free radicals. It is one of the few flavonoids to act simultaneously on mast cells (allergy relief), inflammatory kinases (response to stressors), and the Nrf2 pathway (endogenous antioxidant). Available as a supplement in its free form or combined with bromelain for improved bioavailability.
Quercetin and Allergies: How Does It Work?
Quercetin is one of the few natural active ingredients that acts directly on the mast cell mechanism involved in allergies.
- It inhibits mast cell degranulation—reducing the release of histamine and leukotrienes responsible for allergic symptoms
- Useful for supporting comfort during pollen peaks—see our anti-allergy selection and the allergic rhinitis page
- Not to be confused with prescription antihistamines—quercetin is a supportive supplement
- Can be combined with vitamin C (a cofactor in histamine regulation) and probiotics for comprehensive allergy support
- Category: Allergy dietary supplements available at drugstores
Quercetin and Antioxidants: What Are the Benefits?
Quercetin is one of the most potent flavonoid antioxidants.
- It neutralizes superoxide and hydroxyl radicals more effectively than most flavonoids
- It activates the Nrf2 pathway—stimulating the endogenous production of glutathione and antioxidant enzymes (HO-1, NQO1)
- It protects circulating LDL from oxidation—a key vasoprotective mechanism
- It strengthens and regenerates other antioxidants in the system (vitamin C, glutathione)
- Works synergistically with resveratrol and bioflavonoids to provide comprehensive polyphenolic protection
Quercetin and sports: recovery and endurance?
Quercetin is of particular interest to athletes due to its effects on oxidative stress and muscle comfort.
- It reduces oxidative stress generated by intense exercise—protecting muscle cells
- It supports athletic recovery by modulating the post-exercise oxidative response
- It improves oxygen utilization (VO₂max) according to certain studies on endurance
- It has a short half-life—daily intake is necessary to maintain effective levels
- Combine with sports supplements for antioxidant support during and around exercise
Where can you find quercetin in your diet?
Quercetin is the most common flavonoid in plant-based foods.
- Capers: the most concentrated source (180 mg/100 g)
- Red onions: 35 to 50 mg/100 g—the skin is rich in quercetin
- Apples with the skin on: the predominant flavonoid, better absorbed along with pectin fibers
- Berries: blueberries, black currants, cranberries
- Green tea: synergistic combination of quercetin and catechins
- Red grapes: quercetin + resveratrol — dual antioxidant protection
How should quercetin be used as a supplement?
Supplementation is appropriate for people with increased needs or insufficient dietary intake.
- Typical dosage: 500 to 1,000 mg per day, depending on the goal
- Vitamin C must be taken together: improves absorption by 20 to 30%—vitamin C reduces oxidized quercetin to its active form
- With bromelain: enhances bioavailability and the effect on joint comfort
- With piperine (black pepper extract): absorption improved by 20% in certain formulations
- Interactions to be aware of: anticoagulants (warfarin), immunosuppressants, antihypertensives—inform your doctor
- Mild digestive upset possible at high doses—take in divided doses
