Quercetin (Flavonol · Antioxidant · Mast Cell Stabiliser)
| CAS No. | 117-39-5 |
| Class | Polyphenol · Flavonol · Flavonoid |
| Source | Allium cepa (Red onion) outer scales; also capers, elderberries, buckwheat. Commercial isolate primarily from Sophora japonica flower buds. |
| Claim strength | Moderate |
| Buy from Herbuno | Quercetin Powder 98% → · Liposomal Quercetin 30% Powder → |
Name & isolation: Quercetin derives from the Latin quercetum (oak forest) — first isolated from oak bark by August Husemann in 1857. Traditional context: Plants rich in quercetin (elderflower, chamomile, St John's wort) were central to European herbal anti-inflammatory and anti-allergic practice long before the compound was identified. Mechanism characterised: By the 20th century, quercetin was recognised as a multi-target inhibitor of COX enzymes, lipoxygenase, and phosphodiesterases — and later confirmed as a natural mast cell stabiliser, reducing IgE-mediated histamine release. Commercial source: Most isolate is extracted from Sophora japonica flower buds, hydrolysed from rutinoside to the free aglycone.
Evidence for Antioxidant Defence, Allergy Support & Anti-Inflammatory Activity
Antioxidant and anti-inflammatory: Quercetin scavenges reactive oxygen species, chelates transition metals, and inhibits NF-κB, COX-2, and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). Mechanistic breadth is well-characterised; most evidence is preclinical. Claim strength: Moderate.
Mast cell stabilisation: Inhibits calcium influx into mast cells, reducing IgE-mediated histamine release. A randomised trial documented reduced nasal symptom scores in seasonal allergic rhinitis at 200–400 mg/day. Mechanism is structurally analogous to pharmaceutical cromolyn sodium. Claim strength: Moderate.
Cardiovascular support: Prospective cohorts consistently link higher flavonol intake with lower CVD risk. RCTs at 150–500 mg/day document reductions in blood pressure and LDL oxidation. Evidence for isolated supplementation is weaker than for whole-diet flavonoid intake. Claim strength: Moderate.
Senolytic potential (emerging): The first human senolytic trial (dasatinib + quercetin) demonstrated selective clearance of senescent cells from adipose tissue in diabetic kidney disease patients. Quercetin's standalone senolytic contribution is unestablished. Claim strength: Emerging.
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Dosage, Bioavailability & Formulator Specification
Typical supplement dose: 250–1,000 mg/day aglycone; anti-allergy/anti-inflammatory trials typically use 500–1,000 mg in divided doses.
Bioavailability challenge: Standard quercetin aglycone powder absorbs poorly (<5%). Meaningful improvements: phytosome complex with phosphatidylcholine (2–5× increase), liposomal delivery, or co-formulation with bromelain and vitamin C.
Glycoside vs aglycone: Rutin (quercetin-3-rutinoside) absorbs more slowly via colonic microbiota hydrolysis — preferred for venous tone applications. Aglycone or phytosome achieves higher peak plasma concentrations for systemic antioxidant or anti-inflammatory use.
Synergistic pairs: Bromelain (absorption + anti-inflammatory synergy), pterostilbene (senolytic stack), piperine (modest bioavailability boost), NAC (comprehensive antioxidant formula).
Frequently Asked Questions — Quercetin
Why is quercetin considered a leading dietary antioxidant?
Its pentahydroxy flavonol structure allows simultaneous scavenging of multiple radical species, metal chelation, and inhibition of COX enzymes, lipoxygenases, phosphodiesterases, and NF-κB — making it one of the most mechanistically broad dietary polyphenols studied.
What is the difference between quercetin, rutin, and quercetin phytosome?
Quercetin is the free aglycone. Rutin is quercetin-3-rutinoside — absorbed slowly after gut microbiota hydrolysis. Quercetin phytosome is complexed with phospholipids for significantly improved membrane permeability and plasma bioavailability.
Does quercetin help with seasonal allergies?
Quercetin inhibits calcium influx into mast cells, reducing histamine release — a mechanism analogous to pharmaceutical cromolyn sodium. Limited human trial data supports reductions in nasal allergy symptom scores. Position supplements as supporting a healthy immune response to seasonal environmental factors.
What form of quercetin should I specify for supplement capsules?
98% HPLC-verified aglycone from Sophora japonica is the conventional grade. For premium formulations where bioavailability is critical, liposomal or phytosome quercetin is preferred. Always confirm source botanical and HPLC purity on the CoA.
Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.
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