Quercetin
A bioflavonoid that calms allergic and immune responses, acts as a mild senolytic, and serves as a zinc ionophore — helping zinc get into cells where it does its work.
Moderate evidence for allergy / mast cell stabilisation (less drowsy than antihistamines but slower). Moderate for blood pressure reduction in hypertensives. Senolytic data is preclinical and early-clinical (Kirkland lab — animal trials and small humans). Allergy effects: 2–4 weeks of consistent use.
Quercetin is a flavonoid found in onions, apples, capers, and many berries. It has three distinct supplement uses. First, it stabilises mast cells (reducing histamine release) — useful for seasonal allergies and chronic inflammation. Second, it acts as a zinc ionophore, shuttling zinc across cell membranes — relevant to immune support and the antiviral mechanism that put it in the spotlight during COVID. Third, in combination with dasatinib (a leukemia drug), it has senolytic activity — selectively killing senescent 'zombie' cells. Standalone quercetin is on the milder end of supplements; its value mostly emerges in combinations.
- Form
- Quercetin phytosome (Quercefit) — significantly better absorbed than plain quercetin (~20x). Quercetin + bromelain — traditional pairing for absorption and additional anti-inflammatory action. Plain quercetin dihydrate works but absorbs poorly.
- Dose
- 500–1,000 mg/day for general use. 250–500 mg of Quercefit equivalent. Senolytic protocols use 1,000 mg × 2 days at a time, intermittent.
- Timing
- With food. AM or split AM/PM.
- Schedule
- Daily for allergy / immune support. Intermittent (e.g. 2 days every 2 weeks) for senolytic use.
- Side effects
- Generally well-tolerated. Headache, GI upset, tingling at high doses. Yellow discolouration of urine.
- Interactions
- Cyclosporine (raises levels significantly). CYP3A4 substrates generally — quercetin is a moderate CYP3A4 inhibitor. Anticoagulants (mild additive). Antibiotics (quinolones — opposing antimicrobial effect at gut level).
- Contraindications
- Pre-existing kidney impairment (high doses caused renal toxicity in some early studies). On cyclosporine or other narrow-therapeutic-window drugs.
- Lab markers
- Not typically tested.
- Food sources
- Capers (extremely high), red onions, apples (with skin), kale, broccoli, berries (especially elderberry, cranberry, lingonberry), red wine, green tea, buckwheat. Onions are the most practical source — one large red onion delivers ~50 mg.
Pairs with
Bromelain (absorption + complementary anti-inflammatory). Zinc (quercetin acts as zinc ionophore). Vitamin C (regenerates oxidised quercetin). Fisetin (similar senolytic class).
within Polyphenols & antioxidants