Quercetin
SupplementThe medical score (62) is only slightly below the community score (68), reflecting relatively good alignment between clinical evidence and user reports. Clinical evidence is heterogeneous with small effect sizes [s5, s6], while community perception is moderately positive but tempered by individual adverse event reports [c1, c3].
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TL;DR
Quercetin is one of the most studied flavonoids: meta-analyses show statistically significant but clinically modest effects on blood pressure (−1.96 mmHg) and fasting blood glucose (−1.03 mg/dL), and a COVID-19 meta-analysis suggests reduced hospitalization. Standard quercetin aglycone has poor bioavailability — phytosome formulations or glycosides deliver meaningfully better absorption at the same dose. EFSA has rejected health claims due to insufficient evidence, and senolytic use (e.g., combined with dasatinib) remains purely experimental. Idiosyncratic reactions such as anxiety or severe body pain are rare but documented.
Description
Plant-derived flavonoid with antioxidant and anti-inflammatory properties; commonly used for allergies, cardiovascular prevention, and as a senolytic [s1, s2].
Quercetin is a flavonol (subclass of flavonoids) that occurs naturally in many plants — particularly in onions, apples, capers, berries, and green tea [s1]. As a secondary plant metabolite, it is among the most extensively studied polyphenols. In food, it is primarily bound as a glycoside; the free aglycone form (standard quercetin) has relatively low oral bioavailability due to poor water solubility and rapid intestinal metabolism (glucuronidation) [s1, s2]. Various formulations have been developed to improve bioavailability: phytosomes (Quercefit®) demonstrated up to 20-fold higher absorption than standard quercetin in clinical studies [s4]; enzymatically modified isoquercitrin (EMIQ) and quercetin-3-glucoside are also more bioavailable than the aglycone [s3]. In the field of senolytics (clearance of senescent cells), quercetin is being investigated in combination with the oncology drug dasatinib, with initial clinical pilot data available [s7]. The anti-inflammatory effect, particularly the reduction of inflammatory markers, has been examined in several RCTs and meta-analyses, though the evidence is considered heterogeneous [s5, s6]. In COVID-19, a meta-analysis showed reduced hospitalization and mortality rates [s8]. For sport and physical performance, individual RCTs with moderate effects are available [s9, s10]. EFSA considers the evidence for specific health claims insufficient [s13].
Legal Status (DE)
In Germany, quercetin (from traditional food sources) is marketable as an over-the-counter food supplement (NEM), as it is classified as a foodstuff and requires no authorization [s11]. Quercetin derived from Dimorphandra mollis is considered an unauthorized novel food under EU Regulation (EU) 2015/2283 and may not be sold in this form [s12]. EFSA has not approved any specific health claims for quercetin to date [s13]. No binding maximum levels for quercetin in food supplements exist at either national or EU level [s11].
Mechanism of Action
Quercetin exerts its biological effects through multiple mechanisms [s1, s2]: 1. Antioxidant activity: Quercetin neutralizes reactive oxygen species (ROS) via electron donation from its hydroxyl groups on the aromatic ring. It inhibits lipid peroxidation and protects cell membranes [s1, s2]. 2. Anti-inflammatory action: Quercetin inhibits NF-κB signaling pathways, reduces expression of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), and inhibits cyclooxygenase (COX) and lipoxygenase (LOX) enzymes [s2, s5]. 3. Immunomodulation: Quercetin stabilizes mast cell membranes and inhibits histamine release, explaining its anti-allergic effects. It modulates T-cell and macrophage activity [s1]. 4. Cardiovascular effects: Quercetin inhibits platelet aggregation, reduces endothelial cell inflammation, exerts antihypertensive effects (moderate effects on systolic blood pressure, WMD: −1.96 mmHg in meta-analysis [s6]), and lowers fasting blood glucose (WMD: −1.03 mg/dL [s6]). 5. Senolytic activity (in combination with dasatinib): Quercetin inhibits anti-apoptotic signaling pathways (BCL-2 family, PI3K/AKT) in senescent cells and selectively promotes their apoptosis. Senescence markers (p16, p21) were reduced in obesity and aging models [s7]. 6. Antiviral activity: Quercetin interferes with ACE2 expression, thereby inhibiting SARS-CoV-2 cell entry; in vitro data demonstrate interaction with viral proteases [s8]. The bioavailability of the aglycone form is limited; phytosome formulations significantly increase absorption through binding to phospholipids [s4].
Dosing
Allgemeine antioxidative und entzündungshemmende Unterstützung
- Dose
- 500 mg quercetin (aglycone standard)
- Frequency
- 1–2× täglich
- Route
- oral
- Duration
- bis zu 12 Wochen
- Timing
- With meals (fatty snack improves absorption)
- With food
- empfohlen
Verbesserte Bioverfügbarkeit (Phytosom-Formulierung, z. B. Quercefit)
- Dose
- 250–500 mg phytosomal quercetin (equivalent to 100–200 mg pure quercetin)
- Frequency
- 1–2× täglich
- Route
- oral
- Duration
- bis zu 12 Wochen
- Timing
- With meals
- With food
- empfohlen
Kardiovaskuläre Prävention / Metabolisches Syndrom
- Dose
- 500 mg daily
- Frequency
- 1× täglich
- Route
- oral
- Duration
- 8–12 Wochen
- Timing
- Morning with meals
- With food
- empfohlen
Senolytisch (nur in Kombination mit Dasatinib, experimentell)
- Dose
- 1000 mg quercetin + 100 mg dasatinib (intermittent, e.g. 2 days/week)
- Frequency
- intermittierend (Puls-Protokoll)
- Route
- oral
- Duration
- experimentell, Dauer variiert
- Timing
- Under medical supervision only
- With food
- optional
In clinical studies, doses of up to 1000 mg/day over several weeks have been used without significant adverse effects [s14]. Doses exceeding 2000 mg/day have been associated with renal stress [s14]. No binding EU or national maximum levels for quercetin in food supplements have been established [s11].
The bioavailability of standard quercetin (aglycone) is low; phytosome formulations or quercetin glycosides are more effective at equivalent dose strengths [s3, s4]. Combination with bromelain or vitamin C is frequently reported in the community; clinical evidence for synergism is limited [c2].
Side Effects
| Side Effect | Frequency | Severity |
|---|---|---|
| Kopfschmerzen Occasionally reported in community reports and clinical studies; more frequent at higher doses [s14, c1]. | gelegentlich | leicht |
| Gastrointestinale Beschwerden (Übelkeit, Magenschmerzen) Sporadically reported in studies with up to 1000 mg/day; considered mild and reversible [s14]. | gelegentlich | leicht |
| Kribbeln in Extremitäten (Parästhesien) Reported with high-dose IV administration (not oral); rare with oral supplementation [s14]. | selten | leicht |
| Nierenbelastung bei sehr hohen Dosen Animal studies show nephrotoxic effects at very high doses; in humans, risk is discussed only above 2000 mg/day [s14, c3]. | selten | moderat |
| Körperschmerzen, Angst, Reizbarkeit (idiosynkratisch) Individual community reports; possibly individual intolerance or histamine reaction in MCAS patients [c1, c3]. | selten | moderat |
| DAO-Hemmung (theoretische Histaminakkumulation) Quercetin inhibits the enzyme diamine oxidase (DAO) in vitro, which may be relevant in histamine intolerance or MCAS [c3]. | theoretisch | moderat |
Contraindications
Interactions
Synergistic
Fisetin and quercetin act synergistically as senolytics, more effectively clearing senescent cells in combination. Together they address inflammation, oxidative stress, and cellular aging more broadly than either substance alone.
Quercetin and berberine are combined in longevity concepts and may both activate the AMPK signaling pathway. However, the combination may lead to additive glucose lowering and episodes of dizziness in individuals with prediabetes or those taking metformin.
The combination of quercetin and resveratrol may improve intestinal absorption of resveratrol. In vitro data show that quercetin increases the permeability of resveratrol.
Concomitant use of quercetin and curcumin is feasible and may improve curcumin absorption. Both substances have complementary anti-inflammatory and antioxidant properties.
Quercetin acts as a zinc ionophore, actively transporting zinc into cells and thereby increasing intracellular zinc concentration. This combination is discussed for antiviral effects.
Bromelain enhances intestinal absorption of quercetin and acts synergistically with its antioxidant properties. This combination is frequently used in commercial quercetin preparations.
EGCG and quercetin both act as zinc ionophores and together increase intracellular zinc concentration. This combination may exert synergistic antiviral effects.
Caution
Quercetin metabolites may displace warfarin from human albumin (in vitro, high affinity). Direct CYP2C9 inhibition is weak; nevertheless, caution is advised with concomitant high-dose intake.
Quercetin inhibits the efflux transporter P-glycoprotein and the CYP3A4 enzyme, potentially increasing the bioavailability and plasma levels of cyclosporine, thereby raising the risk of cyclosporine toxicity (nephrotoxicity, immunosuppression).
Quercetin may reduce the absorption and bioavailability of quinolone antibiotics through chelation with divalent cations and inhibition of transport proteins, potentially leading to diminished therapeutic efficacy.
Concomitant use of quercetin and berberine may result in additive blood glucose lowering, particularly in combination with metformin. Dizziness and hypoglycemia-like symptoms have been reported.
As a flavonoid, quercetin may inhibit iron absorption by promoting a more alkaline intestinal environment and forming chelate complexes with iron. Iron supplements should be taken at a time interval from quercetin.
As a flavonoid, quercetin may promote a more alkaline intestinal environment, thereby impairing calcium absorption. Calcium supplements should be taken at a time interval from quercetin.
Studies
Tier A — High Evidence
Outcome: Effect on systemic inflammatory markers (CRP, IL-6, TNF-α)
Effect Size: Heterogeneous results; no consistent significant reduction across all markers
Outcome: COVID-19: hospitalization, ICU admission, LDH activity, mortality
Effect Size: Significant reduction in hospitalization, ICU admission, and mortality; evidence quality moderate
Outcome: Components of metabolic syndrome (fasting blood glucose, blood pressure)
Effect Size: FBG: WMD −1.03 mg/dL (95% CI −1.87 to −0.19); SBP: WMD −1.96 mmHg (95% CI −3.11 to −0.81)
Tier B — Moderate Evidence
Outcome: Post-exercise insulin sensitivity, antioxidant capacity, endurance performance
Effect Size: Improved insulin sensitivity and antioxidant capacity post-exercise; pilot data
Outcome: Athletic performance, oxidative stress, inflammation in athletes
Effect Size: Moderate benefit on oxidative stress; no consistent performance improvement
Outcome: Senescence markers (p16, p21) in adipose tissue following dasatinib+quercetin
Effect Size: Significant reduction of p16 and p21 (p<0.05); metabolic improvements
Tier C — Low Evidence
Outcome: Biological activities, bioavailability, pharmacokinetics
Effect Size: Review; no independent effect size
Outcome: Pharmacological capacity, mechanisms
Effect Size: Review; no independent effect size
Community Evidence
Top reported benefits
- Relief of allergy symptoms (histamine blockade)
- Improved general well-being and reduced signs of inflammation
- Support for exercise and recovery
- Popular combination with bromelain for colds
- Positive reports of MCAS symptom reduction (individual cases)
Top reported issues
- Headaches at higher doses (>500 mg)
- Body aches and irritability (idiosyncratic)
- No noticeable effect in a subset of users
- MCAS patients: partial worsening due to DAO inhibition
- Long-term users report a sense of dependency
Isolated reports of severe adverse effects (anxiety, extreme body pain) at 500 mg/day suggest individual intolerance [c1]. The MCAS community reports both benefit and symptom worsening — DAO inhibition may be relevant [c3]. Long-term data on daily use beyond >12 weeks are limited; users occasionally report unclear symptom changes after several months of use [c4].
Scientific Sources
- Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid
Anand David AV, Arulmoli R, Parasuraman S (2016). Pharmacognosy ReviewsBPMID:28082789DOI - Short-Term Oral Quercetin Supplementation Improves Post-exercise Insulin Sensitivity, Antioxidant Capacity and Enhances Subsequent Cycling Time to Exhaustion in Healthy Adults: A Pilot Study
Lagouge M, Argmann C, Gerhart-Hines Z, et al. (2022). Frontiers in NutritionADOI - Nahrungsergänzungsmittel: Was das Gesetz erlaubt
Verbraucherzentrale Deutschland (2023). Verbraucherzentrale.deBLink - Novel Food Consultation Status: Quercetin from Dimorphandra mollis
European Commission, DG SANTE (2022). European Commission Food SafetyALink - Scientific Opinion on the substantiation of health claims related to quercetin (ID 1647, 1844, 1845, 1846)
EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) (2011). EFSA JournalADOI - Safety of Quercetin Supplementation: A Review of Clinical Trials and Toxicological Studies
Andres S, Pevny S, Ziegenhagen R, et al. (2018). Molecular Nutrition & Food ResearchBPMID:29127724DOI - Quercetin Phytosome – Wirkung und Anwendung
artgerecht.com Redaktion (2023). artgerecht.comCLink - Quercetin: Health Benefits, Side Effects, Uses, Dose & Precautions
RxList Editorial Staff (2023). RxList.comCLink - Evidence for Quercetin as a Dietary Supplement for the Treatment of Cardio-Metabolic Diseases in Pregnancy: A Review in Rodent Models
Mele L, Bidault G, Mena P, et al. (2022). FoodsBDOI - Interaction of quercetin and its metabolites with warfarin: Displacement of warfarin from serum albumin and inhibition of CYP2C9 enzyme
Poór M, Boda G, Needs PW, Kroon PA, Lemli B, Bencsik T (2017). Biomedicine & PharmacotherapyAPMID:28135601DOI - Quercetin, a Flavonoid with Great Pharmacological Capacity
Ullah A, Munir S, Badshah SL, et al. (2020). MoleculesBPMID:33419008DOI - Bioavailability of Quercetin: Problems and Promises
Manach C, Morand C, Crespy V, et al. (1999). Journal of NutritionBPMID:10540999DOI - Improved Oral Bioavailability and Pharmacokinetics of Quercetin Phytosome (Quercefit) vs Standard Quercetin
Riva A, Ronchi M, Petrangolini G, et al. (2019). Journal of Natural ProductsAPMID:30741564DOI - Impact of quercetin on systemic levels of inflammation: a meta-analysis of randomised controlled human trials
Patel RV, Mistry BM, Shinde SK, et al. (2019). European Journal of NutritionAPMID:31213101DOI - The effect of quercetin supplementation on the components of metabolic syndrome in adults: A systematic review and dose-response meta-analysis of randomized controlled trials
Guo XF, Yang B, Tang J, et al. (2024). Phytotherapy ResearchADOI - Senolytic drugs, dasatinib and quercetin, attenuate adipose tissue inflammation, and ameliorate metabolic function in old age
Ogrodnik M, Evans SA, Fielder E, et al. (2021). eLifeCPMID:34309513DOI - The effect of quercetin supplementation on clinical outcomes in COVID-19 patients: A systematic review and meta-analysis
Ziaei S, Aghajani M, Beiraghdar F, et al. (2023). Food Science & NutritionAPMID:38107122DOI - Quercetin in Sports and Exercise: A review
Kaur G, Silber A, Goss AM, et al. (2024). NutrientsBDOI
Community Sources
Storage
Unopened
Store in a dry, cool place at room temperature (15–25 °C), protected from direct sunlight.
Opened
Keep container tightly closed; avoid moisture and heat sources; consume within the printed expiry date.
Notes
Quercetin is light-sensitive and may degrade upon prolonged UV exposure. Store phytosome formulations according to manufacturer instructions.