Why Quercetin Is a Foundational Supplement in Functional Medicine

Quercetin is frequently incorporated into Sanctuary protocols because of its wide-ranging therapeutic benefits. This naturally occurring flavonoid is best known for its role in allergy support, antioxidant protection, prevention of LDL cholesterol oxidation, and assistance with metal detoxification. Emerging research has also identified additional benefits, including support for prostatitis, modest effects on blood pressure and blood sugar regulation, and antiviral activity, an area that gained increased attention during the COVID-19 pandemic pasted.

Key Clinical Benefits of Quercetin

Allergy and Mast Cell Support

One of the most common uses of quercetin in functional medicine is for allergy management. It may benefit individuals with seasonal allergies, food sensitivities, sinus congestion, and mast cell activation by reducing histamine-driven responses.

Quercetin works through two primary mechanisms:

• Inhibiting histamine release from mast cells

• Reducing IgE-mediated immune reactions that trigger histamine release

Mast cell stabilization is especially important in patients with mold toxicity, where immune overactivation can significantly complicate treatment. By stabilizing mast cells, quercetin helps reduce histamine and other inflammatory mediators that contribute to symptoms.

Many long-term allergy sufferers find that consistent quercetin use allows them to reduce or discontinue antihistamines and nasal steroids under provider guidance.

Cardiovascular and Cholesterol Support

Oxidized LDL cholesterol plays a central role in the development of atherosclerosis by triggering immune-mediated inflammation within arterial walls. Quercetin helps reduce LDL oxidation, potentially slowing plaque formation.

Research has shown that quercetin intake may be associated with reduced cardiovascular mortality, likely due to its antioxidant activity and ability to chelate metals. There is also emerging interest in its possible effects on mast cells and histamine, which may contribute to certain non-cholesterol-related cardiovascular events.

Heavy Metal Detoxification

Quercetin has demonstrated protective effects against heavy metal toxicity, including lead and cadmium, in animal studies. These effects appear to involve modulation of inflammatory and detoxification pathways such as metallothionein, nitric oxide synthases (NOS), COX-2, MAPK, and NF-κB.

Antioxidant Protection

Quercetin possesses significant antioxidant capacity and is often compared to curcumin in its ability to neutralize free radicals and reduce oxidative stress throughout the body.

Prostate Health

In clinical research involving men with chronic prostatitis, quercetin supplementation (500 mg twice daily for one month) resulted in statistically significant improvements in prostate symptoms. Approximately 67% of participants reported improvement compared to 20% in the placebo group. Pain and quality of life improved, although some urinary symptoms persisted.

Blood Pressure and Blood Sugar Effects

Quercetin’s effects on blood pressure and blood sugar appear modest but clinically relevant. Studies have shown average reductions of 2–3 mmHg in blood pressure, while blood sugar changes have been minimal and inconsistent across studies. These effects should be considered as supportive rather than primary therapeutic benefits.

Antiviral Properties

Increased interest in antiviral support during 2020 brought attention to quercetin’s potential role in both prevention and adjunctive treatment of viral infections. Several studies suggest quercetin may interfere with viral replication and support immune defense mechanisms.

Areas of Ongoing Research

Additional areas under investigation—though currently lacking sufficient evidence for clinical recommendations—include:

• Sleep

• Exercise performance

• Cancer support

• Cognitive and memory function

• Arthritis

How to Take Quercetin

While quercetin is present in many foods, therapeutic doses for symptomatic patients are rarely achieved through diet alone. The highest dietary concentrations are found in capers and the outer layers of onions. Other sources include apples, berries, kale, broccoli, green beans, black tea, chili powder, and alfalfa sprouts.

For clinical treatment, supplementation is typically required. Food sources are more effective for long-term preventive support.

Dosing for Allergies

Quercetin works by preventing histamine release rather than stopping an active allergic reaction. Most patients require twice-daily dosing for 3–4 days before noticing improvement, with maximal benefit typically reached by day 7. Doses may be adjusted based on symptom persistence, and some individuals may require higher or more frequent dosing.

Potential Side Effects and Considerations

Allergic Reactions

Although rare, allergic reactions to quercetin can occur. These are typically mild, and blood testing may help identify sensitivities if symptoms arise.

Mold Toxicity Sensitivity

Patients with mold toxicity can be exceptionally sensitive to supplements. In some cases, quercetin—despite its mast cell-stabilizing properties—may trigger paradoxical reactions. These often resolve as detoxification progresses, but some patients may not tolerate standard doses.

Gastrointestinal Symptoms

Mild nausea can occur, particularly in individuals with sensitive stomachs. Taking quercetin with food often reduces this effect.

COMT Considerations

Concerns have been raised regarding quercetin’s potential to inhibit COMT (catechol-O-methyltransferase), an enzyme involved in neurotransmitter and estrogen metabolism. While quercetin can slow COMT activity in laboratory settings, human studies indicate that clinically relevant inhibition would require unrealistically high doses. As a result, quercetin is not routinely restricted in patients with COMT genetic variants.

Quercetin can be a powerful tool when used thoughtfully and in the right clinical context. If you’re dealing with allergies, histamine issues, cardiometabolic risk, or immune imbalance, our team can help determine whether it belongs in your personalized care plan.

Schedule a consultation with Sanctuary Functional Medicine.

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ACRONYM KEY: NF kappa B – Nuclear Factor kappa B.  This protein plays a central role in promoting inflammation.  A wide variety of triggers set off a cascade of downstream processes that all begin with NF kappa B.  Once NK kappa B is triggered, these downstream processes carry out the metabolic pathways which produce what we perceive as inflammation.   COX-2: Cyclo-oxygenase 2 enzyme.  This enzyme plays an important role in the inflammatory pathway.  By converting arachidonic acid, an omega 6 fatty acid associated with inflammation, into prostaglandins, COX-2 sets off a cascade of processes leading to prostaglandins which cause inflammation.  While a similar enzyme called COX-1 is always working at a relatively consistent low level, COX-2 is activated with inflammation.   NOS:  inducible Nitric Oxide Synthase.  This is one of the three enzymes responsible for producing nitric oxide in the body.  NOS2 is the gene which produces this enzyme.  This form is found in immune cells that are used to attack invaders like bacteria with oxidation.  NOS is inducible because it is turned on when a need for immune defense is identified but turned down when the perceived threat is over.        

Weng, Zuyi et al. “Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans”

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