Unpacking the Nutritional Profile of Quercetin: What is the profile of quercetin?

October 5, 2025 •

3 min read

Quercetin is the most abundant flavonoid consumed in the human diet, with an estimated daily intake of 10–100 mg from various food sources. Understanding what is the profile of quercetin reveals its significant role as a powerful antioxidant and anti-inflammatory compound with extensive health potential.

Quick Summary

Quercetin is a powerful antioxidant flavonoid found in plant-based foods, known for its anti-inflammatory, anti-allergic, and antimicrobial properties. Its health effects and bioavailability depend on its food source, form, and metabolism within the body.

Key Points

Flavonoid Antioxidant: Quercetin is a potent plant pigment and flavonoid known for its powerful antioxidant properties that combat cell-damaging free radicals.
Rich Food Sources: It is abundant in foods like capers, red onions, berries, grapes, and apples, often found concentrated in the outer layers of plants.
Low Bioavailability: Quercetin has poor water solubility and low oral bioavailability, which is a major challenge for its use as a therapeutic agent.
Metabolism is Key: After absorption, quercetin is extensively metabolized in the body into various conjugated metabolites, which are believed to be the primary bioactive forms.
Health Benefits: The flavonoid is associated with numerous health benefits, including anti-inflammatory, anti-allergic, and cardioprotective effects.
Form Matters: Absorption and efficacy are heavily influenced by the form of quercetin (aglycone vs. glycoside) and co-factors like vitamin C or bromelain.

What is Quercetin? Exploring Its Chemical and Natural Identity

Quercetin is a plant pigment belonging to the flavonoid group, found in various fruits, vegetables, grains, and beverages. It is a flavonol with the chemical formula C15H10O7 and five hydroxyl groups, essential for its potent antioxidant activity. The name "quercetin" comes from the Latin word for “oak forest”.

In food, quercetin mainly exists as glycosides, meaning it's attached to sugar molecules, which affects its absorption and solubility. While naturally found in plant-based foods, it's also available as a dietary supplement.

Natural Sources of Quercetin

Quercetin is widespread in plants, with concentrations varying by food type and plant part. Higher levels are often in skins and leaves, and light can increase its production.

List of Quercetin-Rich Foods

Capers: Raw capers have the highest concentration.
Onions: Red and yellow onions are rich sources, particularly in their outer layers.
Apples: The skin of red apples contains quercetin.
Berries: Blueberries, cranberries, and raspberries are good sources.
Grapes: Red grapes and red wine also provide this flavonoid.
Tea: Both green and black tea contain quercetin.
Cruciferous vegetables: Broccoli and kale are also good sources.
Peppers: Yellow and green bell peppers contribute to dietary intake.

The Extensive Health Benefits of Quercetin

Quercetin has been widely studied for its potential health benefits.

Antioxidant and Anti-inflammatory Properties

Known for its powerful antioxidant and anti-inflammatory effects, quercetin combats free radicals that cause cellular damage and are linked to chronic diseases. It reduces oxidative stress and suppresses pro-inflammatory molecules, potentially helping manage inflammation-related conditions.

Anti-Allergic Effects

Quercetin acts as a natural antihistamine by stabilizing mast cells and preventing histamine release, which may help relieve allergy symptoms. Animal studies show promise in suppressing allergic reactions.

Cardiovascular Health

Research suggests quercetin may protect the heart, potentially lowering blood pressure and improving blood vessel function. It appears to relax blood vessels and may inhibit factors involved in heart disease. Human studies, especially with supplement doses over 500 mg daily, have shown reductions in blood pressure.

Potential Anti-Cancer Effects

Laboratory and animal studies indicate potential anticancer effects, including suppressing cancer cell growth and inducing cell death in various cancer types like prostate, liver, and breast cancer. It may also enhance the effectiveness of chemotherapy drugs.

Comparing Bioavailability of Quercetin from Food and Supplements

Quercetin has notoriously low oral bioavailability, meaning limited absorption into the bloodstream. This varies based on its form and if consumed with other compounds.


Feature	Quercetin from Food (e.g., Onions)	Quercetin from Supplements	Key Differences
Form	Primarily as glycosides (attached to sugar molecules).	Can be aglycone or mixed with enhancers like bromelain or vitamin C.	Glycoside forms can be more water-soluble and better absorbed via specific transporters (SGLT-1).
Absorption Rate	Glucosides (from onions) are absorbed more quickly and efficiently in the small intestine.	Absorption is generally lower for aglycone forms unless enhanced by other compounds.	Food matrix and form of quercetin play a significant role in absorption efficacy.
Metabolism	Metabolized in the intestine and liver into various conjugated metabolites.	Similarly metabolized, but with potentially different metabolite profiles based on the initial form.	The ultimate bioactive compounds in the body are the metabolites, not the quercetin itself.
Bioavailability Enhancements	Naturally co-occurs with other compounds that can influence its metabolism. Co-ingestion with fat can also help.	Formulations often include bromelain or vitamin C to improve absorption and efficacy.	Supplements offer targeted enhancement but may not fully replicate the benefits of a complex food matrix.
Drug Interactions	Potential for interaction is present but less concentrated than with high-dose supplements.	Higher doses increase the risk of interacting with medications, particularly blood thinners and certain antibiotics.	Medical supervision is recommended for high-dose supplements.

Factors Influencing Bioavailability

Food Form: The presentation of quercetin in food affects absorption; glucosides from onions are more bioavailable than rutinoside from apples.
Co-Administration: Consuming quercetin with fat, bromelain, or vitamin C can enhance its absorption.
Nanotechnology: New delivery systems like nanoformulations are being developed to improve quercetin's solubility and bioavailability for therapeutic use.

Conclusion

The profile of quercetin reveals its powerful antioxidant and anti-inflammatory properties, presence in plant-based foods, and unique metabolism. Despite potential benefits for cardiovascular health and allergies, its low bioavailability challenges supplementation. The form consumed, whether food glycosides or enhanced supplements, significantly impacts effectiveness. Eating quercetin-rich foods is the most natural way to benefit. For supplements, understanding bioavailability and drug interactions is crucial. Research continues to explore delivery methods to maximize its therapeutic potential.

Visit PubChem to view the chemical structure of quercetin.

Frequently Asked Questions

Quercetin is a plant pigment, specifically a type of flavonoid, with potent antioxidant and anti-inflammatory properties. It is found naturally in many fruits, vegetables, and grains.

While many plant-based foods contain quercetin, some of the richest sources include capers, red onions (especially the outer layers), apples, berries, and green tea.

Quercetin is known for its antioxidant effects, its potential to reduce inflammation, its anti-allergic properties by acting as a natural antihistamine, and its potential cardiovascular benefits like lowering blood pressure.

Absorption depends on its form. Quercetin glucosides from certain foods, like onions, are often better absorbed than the pure aglycone form found in many supplements. However, supplements can be formulated with enhancers like bromelain to improve bioavailability.

Yes, high-dose quercetin supplements can interact with certain medications, including blood thinners and antibiotics. It is important to consult a healthcare provider before taking quercetin supplements, especially if you have pre-existing health conditions or are on medication.

Quercetin's oral bioavailability is notoriously low due to poor water solubility and rapid metabolism in the body. After ingestion, it is quickly metabolized in the gut and liver into conjugated metabolites.

There is not enough reliable information to know if quercetin is safe for use during pregnancy or breastfeeding. It is best to avoid its use during these periods to stay on the safe side.