Quercetin
Plant flavonoid with meta-analysis signal for modest blood pressure reduction and an emerging signal for allergic rhinitis.
Why
Quercetin is a flavonol found in onions, apples, capers and green tea. Meta-analyses of RCTs report modest systolic blood pressure reductions at ≥500 mg/day, with effect more consistent in metabolic syndrome and hypertensive populations. Smaller bodies of work support use in seasonal allergic rhinitis (via mast cell stabilisation) and as a marker-of-interest in early COVID research, though clinical conclusions there remain preliminary. Bioavailability is poor, phytosome and EMIQ (enzymatically modified isoquercitrin) forms have meaningfully better absorption.
How it works
Mast cell stabiliser (reduces histamine and tryptase release), basis of the allergic rhinitis signal. Inhibits xanthine oxidase, has mild ACE-inhibitory activity, and modulates vascular endothelial function via nitric oxide pathway.
Expected onset · BP effects over 4–8 weeks; allergic rhinitis effects within 1–2 weeks
How to take
Dosage
500–1,000 mg/day, often divided. EMIQ or phytosome forms: 250–500 mg/day with better bioavailability.
Timing
Divided 2–3 times daily with food
On the label
EMIQ (enzymatically modified isoquercitrin) or quercetin phytosome (Quercefit) for better absorption. Plain quercetin aglycone is poorly absorbed.
Ideal for
Adults with mild hypertension or seasonal allergic rhinitis exploring nutrient adjuncts.
Safety
Evidence
Serban 2016 J Am Heart Assoc meta-analysis (7 RCTs): quercetin ≥500 mg/day reduced systolic BP by 3.04 mmHg and diastolic by 2.63 mmHg vs control. Effect modest and most consistent in metabolic syndrome and hypertensive groups. Allergic rhinitis evidence is preclinical-strong but clinical-trial-thin. Practical limit is bioavailability, choose a phytosome or EMIQ form.
Where to get it
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