Quercetin Extract – Effects, Uses and Dosage

What is Quercetin Extract?

Quercetin extract is a concentrated plant-based extract containing the secondary plant compound quercetin. Quercetin belongs to the flavonoid family – naturally occurring polyphenolic compounds found in many fruits and vegetables, well known for their potent antioxidant activity. The extract is derived from quercetin-rich plants such as onions, apples, capers, broccoli, and buckwheat, and is used in concentrated form as a dietary supplement or botanical remedy.

Active Compounds and Mechanism of Action

The primary active compound in quercetin extract is the flavonoid quercetin (3,3',4',5,7-pentahydroxyflavone). It exerts its effects through multiple mechanisms:

• Antioxidant activity: Quercetin neutralizes free radicals and protects cells from oxidative stress, which is associated with chronic disease and aging.
• Anti-inflammatory effects: It inhibits pro-inflammatory enzymes such as COX-1, COX-2, and lipoxygenase, and reduces the release of cytokines including TNF-alpha and interleukin-6.
• Antihistamine effects: Quercetin stabilizes mast cells and inhibits the release of histamine, making it relevant in the context of allergic reactions.
• Antiviral properties: Laboratory studies have demonstrated that quercetin can inhibit certain viruses by interfering with their entry into cells and subsequent replication.
• Cardioprotective effects: Quercetin can inhibit platelet aggregation, lower blood pressure, and improve vascular function.

Traditional Use

Quercetin has been part of traditional herbal medicine for centuries. Plants with a high quercetin content – such as onions, capers, and apples – were used in folk medicine to support respiratory health, reduce inflammation, and generally strengthen the immune system. In modern phytotherapy, quercetin extract is specifically used for allergic conditions, chronic inflammation, and antioxidant support.

Medical Applications

Quercetin extract is investigated and used in practice and research for the following areas:

• Allergies and hay fever: Due to its antihistamine activity, quercetin is used to relieve symptoms such as sneezing, runny nose, and watery eyes.
• Chronic inflammation: In conditions such as arthritis, inflammatory bowel disease, or atherosclerosis, quercetin may help modulate inflammatory processes.
• Cardiovascular health: Clinical studies suggest that quercetin can modestly reduce systolic blood pressure and improve endothelial function.
• Immune support: Quercetin supports immune defense and is frequently combined with vitamin C and zinc to enhance immune function.
• Athletic performance and recovery: Due to its antioxidant and anti-inflammatory properties, quercetin extract is also used in sports nutrition to support recovery.
• Anti-aging (senolytics): As a potential senolytic agent, quercetin may help clear senescent cells – cells that have stopped dividing but contribute to tissue inflammation and aging.

Recommended Dosage

There is no officially established daily dose for quercetin extract. Clinical studies have commonly used dosages between 500 mg and 1000 mg per day, divided into two doses. Higher dosages should only be taken following medical advice. The bioavailability of quercetin is naturally low, which is why many supplements use quercetin phytosome complexes or combine it with bromelain or vitamin C to enhance absorption.

Safety and Side Effects

Quercetin extract is generally considered well tolerated at recommended doses. Possible side effects at higher doses may include:

• Headaches
• Tingling sensations in the extremities
• Gastrointestinal discomfort or nausea

At very high doses (above 1 g/day over extended periods), potentially nephrotoxic (kidney-damaging) effects have been discussed, although human data remain limited. Pregnant and breastfeeding women, as well as individuals taking anticoagulant medications such as warfarin, should use quercetin extract only after consulting a physician.

Interactions

Quercetin may interact with certain medications:

• Anticoagulants (blood thinners): Quercetin may enhance the effect of blood-thinning medications.
• Antibiotics (fluoroquinolones): Quercetin may affect the absorption of certain antibiotics.
• Cyclosporin and other immunosuppressants: Possible interactions via hepatic metabolism (CYP3A4 inhibition) have been reported.

It is always recommended to consult a physician or pharmacist before combining quercetin extract with medications.

References

1. Lakhanpal P, Rai DK. Quercetin: A Versatile Flavonoid. Internet Journal of Medical Update, 2007; 2(2): 22-37.
2. Boots AW, Haenen GR, Bast A. Health effects of quercetin: from antioxidant to nutraceutical. European Journal of Pharmacology, 2008; 585(2-3): 325-337. DOI: 10.1016/j.ejphar.2008.03.008.
3. European Food Safety Authority (EFSA). Scientific Opinion on the safety of quercetin as a food supplement. EFSA Journal, 2011; 9(7): 2265. DOI: 10.2903/j.efsa.2011.2265.