Quercetin
Also known as: quercetin dihydrate, quercetin phytosome, Quercefit, EMIQ
Recommended Dosage
500–1000 mg
Quercetin is a ubiquitous flavonoid found in onions, apples, and berries that exhibits anti-inflammatory, antioxidant, and senolytic (clearing senescent cells) properties. It functions as a zinc ionophore, enhancing zinc's antiviral activity, and has been studied for immune support during respiratory infections. The phytosome form (Quercefit) offers dramatically improved bioavailability — approximately 20 times higher than standard quercetin dihydrate.
TL;DR: Versatile flavonoid with senolytic, immune, and anti-inflammatory properties. Zinc ionophore. Phytosome form critical for absorption.
Quick Facts
Evidence
Grade B
Studies
3
Interactions
3
Forms
1
Evidence Rating: Grade B — Moderate Evidence
Some RCTs with positive results, or strong observational evidence. More research may refine our understanding.
Interaction Warnings
Inhibits P-glycoprotein; potential toxicity increase
CYP2C9 inhibitor; may increase warfarin levels — monitor INR
May reduce antibiotic absorption — separate by 2+ hours
Important Notes
- Phytosome form has 20x better bioavailability
- High doses (>3g/day): possible kidney damage
- Also a zinc ionophore — enhances zinc cellular uptake
Clinical Evidence (3 studies)
Quercetin reduced URTI in athletes
Somerville VS et al. (2016) — Nutrients
Meta-analysis of 5 RCTs: modest but significant URTI prevention
View on PubMedQuercetin phytosome reduced SARS-CoV-2 infection
Di Pierro F et al. (2021) — Int J Gen Med
Significantly reduced infection rates; RCT
View on PubMedQuercetin reduced cold/flu symptoms in stressed adults
Heinz SA et al. (2010) — Eur J Nutr
1,000mg/day for 12 weeks reduced URTI sick days
View on PubMedAlternatives to Consider
These supplements target similar goals and may be worth considering alongside or instead of Quercetin.
Spirulina
Grade BNutrient-dense cyanobacterium with strong evidence for immune support, lipid improvement, and antioxidant protection. Complete protein source. Quality sourcing is critical to avoid contamination.
Turkey Tail Mushroom
Grade BMost-studied medicinal mushroom for immune support. PSK/PSP polysaccharides are approved as anticancer adjunct therapy in Japan. Strong evidence for immune modulation and gut microbiome support.
Chlorella
Grade CGreen algae rich in chlorophyll, protein, iron, and B12. Evidence for immune support and metabolic markers. Broken-cell wall form required for bioavailability. Complementary to spirulina.
Related Supplements
Spirulina
Grade B — Moderate EvidenceNutrient-dense cyanobacterium with strong evidence for immune support, lipid improvement, and antioxidant protection. Complete protein source. Quality sourcing is critical to avoid contamination.
Chlorella
Grade C — PreliminaryGreen algae rich in chlorophyll, protein, iron, and B12. Evidence for immune support and metabolic markers. Broken-cell wall form required for bioavailability. Complementary to spirulina.
Turkey Tail Mushroom
Grade B — Moderate EvidenceMost-studied medicinal mushroom for immune support. PSK/PSP polysaccharides are approved as anticancer adjunct therapy in Japan. Strong evidence for immune modulation and gut microbiome support.
Astragalus
Grade C — PreliminaryFoundational Traditional Chinese Medicine herb with immune-modulating and potential anti-aging properties. Astragalus polysaccharides support immune function, and cycloastragenol may activate telomerase. Mostly preclinical evidence but long traditional use. Avoid with immunosuppressants.
🧪 Get Your Personalized Stack
See how Quercetin fits with your goals and current supplements — AI-powered, evidence-graded recommendations.
⚕️ Important Disclaimer
This information is for educational purposes only. It is not medical advice. Always consult a healthcare provider before starting any supplement regimen, especially if you take medications or have health conditions.
DoseGrade does not sell supplements and has no affiliate relationships with supplement manufacturers.