Quercetin

Also known as: Quercetin dihydrate · Quercetin phytosome · Quercefit

●●○Moderate Evidence

A flavonoid in onions, apples, and capers. Acts as a zinc ionophore (shuttles zinc into cells), has antiviral properties, and modestly improves endurance and allergy symptoms.

Effective Dose

500–1000mg / day

per clinical evidence

Evidence Level

Moderate

Anti-Inflammation & Antioxidants

Mechanism

Zinc ionophore, antiviral, anti-inflammatory (NF-κB, MAPK inhibition)

primary action

Best For

Immune health

Endurance, Allergy relief, Antiviral

This profile is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before starting any supplementation, especially if you have pre-existing conditions or take medications.

What Is Quercetin?

Quercetin is among the most abundant dietary flavonoids. It has multiple mechanisms of action: zinc ionophore activity (shuttling zinc across cell membranes to inhibit viral RNA polymerases), NF-κB inhibition, histamine stabilisation in mast cells, and eNOS activation. Bioavailability is low with standard quercetin — phytosome forms improve absorption significantly.

How It Works: The Science

As a zinc ionophore, quercetin binds Zn²⁺ and facilitates its transport into cells, where zinc inhibits viral RNA-dependent RNA polymerase — a broad antiviral mechanism. Quercetin directly inhibits COMT (catecholamine metabolism), NF-κB (inflammation), and H1 histamine release from mast cells (antiallergic). It also inhibits HIF-1α, supporting oxygen metabolism during exercise.

Primary Mechanism

Zinc ionophore, antiviral, anti-inflammatory (NF-κB, MAPK inhibition)

Evidence-Based Benefits

Reduces upper respiratory illness in athletes during intensified training

moderate

Nieman et al. (2010) — 1g/day significantly reduced illness incidence post-ultra-marathon

Improves VO₂max and endurance performance

moderate

Nieman et al. (2010) — 1g/day for 2 weeks improved VO₂max by 3.9% vs placebo

Reduces allergy and hay fever symptoms

moderate

Mast cell stabilisation — comparable to some antihistamines in small trials

Dosage Guide

Effective Dose

500–1000mg / day

500–1000mg/day. Quercefit (phytosome) or EMIQ are enhanced bioavailability forms. Take with zinc for synergistic antiviral effect. Vitamin C helps recycle oxidised quercetin back to its active form.

Safety Profile & Side Effects

Generally very safe. Possible theoretical interactions with blood thinners (quercetin inhibits platelet aggregation) and thyroid medication at very high doses. Safe at 1g/day in published trials.

Who Should (and Shouldn't) Take It

Best for

Immune healthEnduranceAllergy reliefAntiviral

Who it's for

Endurance athletes with high infection risk (post-competition immunosuppression), allergy sufferers, and those wanting broad antioxidant and antiviral immune support.

Frequently Asked Questions

What is the recommended dose of Quercetin?

Is Quercetin safe?

Generally very safe. Possible theoretical interactions with blood thinners (quercetin inhibits platelet aggregation) and thyroid medication at very high doses. Safe at 1g/day in published trials.

How does Quercetin work?

Who should take Quercetin?

Endurance athletes with high infection risk (post-competition immunosuppression), allergy sufferers, and those wanting broad antioxidant and antiviral immune support.

Related Ingredients

Zinc (Bisglycinate / Picolinate)Vitamin C (Ascorbic Acid)Curcumin (with Bioperine / Phytosome)Omega-3 (EPA + DHA)

Medical Disclaimer

Ingredient profiles are for informational purposes only and do not constitute medical advice. Consult a qualified healthcare professional before starting any supplementation, especially if you have pre-existing conditions or take medications. Full disclaimer →