Sophora japonica: Quercetin, Flavonoids & Research

This page is part of the AMLApure Ingredient Science Library. It is intended for holistic, integrative, and nutrition-focused healthcare professionals and scientifically interested consumers. Content is educational and does not constitute medical advice.

Sophora japonica: Quercetin, Flavonoids & Botanical Research

What Is Sophora japonica?

Sophora japonica is the historically established common name for a deciduous tree native to China and East Asia, now widely cultivated across temperate regions worldwide. In current botanical taxonomy, the tree has been reclassified and is now formally named Styphnolobium japonicum (L.) Schott — a member of the Fabaceae (legume) family. The reclassification reflects updated phylogenetic analysis but has no bearing on the traditional or commercial use of the plant.

The name Sophora japonica remains in widespread commercial, regulatory, and scientific use — it appears consistently in supplement labeling, trade documentation, and much of the published flavonoid literature. This page uses both names and acknowledges the current accepted scientific nomenclature.

Despite its species epithet japonicum, the tree is of Chinese origin, not Japanese. It has been cultivated in Japan and widely across East Asia for centuries and is recognized as the official city tree of Beijing.

Botanical Source

The part of the plant most commonly used as a source of flavonoids — particularly rutin and quercetin — is the flower bud (Flos Sophorae Immaturus in traditional Chinese botanical terminology). The immature (unopened) flower buds are harvested before bloom and are recognized as containing high concentrations of rutin, which serves as the primary flavonoid source in commercial Sophora japonica extract production.

The mature flower, the pod, and other parts of the plant have also been used in traditional practice, but the flower bud is the primary commercial source for flavonoid standardization.

AMLApure formulation note: The current AMLApure product descriptions list quercetin as an ingredient across the Enterinex™ product range. The product pages do not specify the botanical source of quercetin used (e.g., Sophora japonica, buckwheat, or another source). This page describes Sophora japonica as a major commercial source of quercetin ingredients, which is accurate in a general botanical context. AMLApure’s actual quercetin ingredient source should be verified on the current product label or Certificate of Analysis.

Quercetin, Rutin & Flavonoids

Sophora japonica flower bud extracts are characterized primarily by their rutin content. Rutin (quercetin-3-O-rutinoside) is a flavonoid glycoside — essentially quercetin bound to the disaccharide rutinose. Rutin is itself a naturally occurring flavonoid with its own studied properties, but it is also the primary industrial precursor from which quercetin is commercially produced.

In supplement manufacturing, rutin extracted from Sophora japonica buds is typically hydrolyzed — enzymatically or chemically — to cleave the sugar moiety and release the aglycone (free form) quercetin. The resulting quercetin ingredient is sometimes referred to as “quercetin from Sophora japonica” or “quercetin (as Sophora japonica extract)” on product labels.

Key distinctions:

  • Rutin and quercetin are related but distinct compounds with different chemical structures, different bioavailability profiles, and separate bodies of research
  • Sophora japonica extract standardized for rutin is not interchangeable with a quercetin aglycone preparation derived from it
  • Not all Sophora japonica extracts contain identical flavonoid concentrations — content varies with plant material quality, harvest timing, extraction method, and standardization specification

What Is Quercetin?

Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is a naturally occurring flavonol — a subclass of flavonoids — found across a wide range of plant foods. It is one of the most studied dietary polyphenols in nutritional science.

Common food sources of quercetin include:

  • Capers (one of the most concentrated food sources)
  • Red and yellow onions
  • Apples (particularly in the skin)
  • Broccoli and leafy greens
  • Berries (elderberries, blueberries, cranberries)
  • Green tea
  • Red wine (as part of grape skin polyphenols)
  • Buckwheat

Quercetin is classified as an antioxidant flavonoid — it has the structural features (hydroxyl groups on a flavone backbone) that allow it to donate electrons or hydrogen atoms to reactive oxygen species under laboratory conditions. This in vitro antioxidant activity is well-documented and is a basis for its use in nutritional formulations.

Quercetin also occurs naturally in amla (Phyllanthus emblica) alongside other polyphenolic compounds. For the full phytochemistry of amla, see amla polyphenol and Vitamin C science — Amla Ingredient Science Library.

Quercetin Bioavailability

Quercetin’s absorption and metabolism in the human body is a nuanced topic that is important for understanding its nutritional utility.

Key bioavailability considerations:

  • Chemical form matters: Quercetin aglycone (the free form) and quercetin glycosides (such as rutin, quercetin-3-glucoside) are absorbed via different mechanisms and at different rates. Quercetin-3-glucoside (found in onions) tends to be more rapidly absorbed than quercetin aglycone or rutin in human studies.
  • Food matrix effects: Quercetin consumed as part of a whole food is absorbed differently than quercetin in an isolated supplement preparation. Fat-soluble co-ingestion, fiber content, and gut microbiome composition all influence absorption.
  • Individual variability: Absorption varies substantially between individuals. Gut microbial activity plays a role in quercetin metabolism; some individuals are “high absorbers” and others “low absorbers” based on microbial phenotype.
  • Piperine: Some formulations include piperine (black pepper extract) with quercetin. A small body of research suggests piperine may influence the metabolism of certain polyphenols. AMLApure’s Enterinex™ formulations include piperine as part of the ingredient system; this page does not claim a specific bioavailability enhancement without direct evidence on those particular formulations.

This page does not claim a specific absorption percentage for any AMLApure quercetin formulation, and does not assert superior bioavailability without direct comparative evidence.

Antioxidant & Cellular Research

Quercetin has been extensively studied in laboratory (in vitro) and preclinical settings for its antioxidant and cellular properties.

In vitro (laboratory cell studies):
Quercetin has demonstrated free-radical scavenging activity in numerous assays, including DPPH, ORAC, and FRAP measurements. In cell culture models, quercetin has been studied for its interactions with signaling pathways related to oxidative stress, including Nrf2 activation — a transcription factor involved in the regulation of antioxidant defense genes. These are mechanistic findings in controlled laboratory conditions.

Important limitation: In vitro antioxidant assay results do not directly predict equivalent outcomes in human physiology. Absorption, tissue distribution, metabolism, and the complexity of the in vivo environment mean that laboratory antioxidant activity does not automatically translate to a clinical antioxidant benefit in humans.

Cellular and mechanistic research:
Quercetin has been studied in cell and animal models in the context of histamine metabolism, mast cell activity, and signaling pathways related to normal immune function. These mechanistic findings have informed human research hypotheses but should not be presented as established human clinical outcomes.

Mechanistic ≠ clinical: The presence of in vitro or animal data for a compound does not establish that the same effect occurs in humans at nutritional doses.

Human Research

The human research base for quercetin is more developed than for many individual flavonoids, though limitations in study quality, dose consistency, and preparation variability apply throughout.

Areas with published human research (RCTs and controlled trials):

  • Antioxidant status markers: Some human studies have measured changes in plasma antioxidant markers following quercetin supplementation. Results across trials are mixed, with some showing modest changes and others showing no significant effect. Findings depend heavily on dose, form, population, and baseline oxidative status.
  • Blood pressure: A small number of randomized controlled trials have examined quercetin supplementation in relation to blood pressure. One meta-analysis (Serban et al., 2016, Journal of the American Heart Association) pooled data from several RCTs and reported a statistically significant but modest effect of quercetin on systolic and diastolic blood pressure compared to placebo. Study populations, doses, and durations varied considerably. This does not establish that quercetin treats hypertension.
  • Lipid markers: Some human studies have examined quercetin in relation to lipid profiles. Evidence is mixed; findings in at-risk populations have not been consistently reproduced across studies.
  • Immune and respiratory function: Several human trials have examined quercetin in the context of upper respiratory tract infections and immune function measures. Results are preliminary and inconsistent. These findings should not be interpreted as establishing that quercetin prevents or treats infectious disease.
  • Exercise and recovery: A limited body of human research has examined quercetin in the context of exercise-induced oxidative stress and recovery markers. Evidence is insufficient to draw broad conclusions.

Critical distinction — quercetin vs. Sophora japonica extract:
Most of the human clinical research above was conducted using isolated quercetin aglycone preparations, not Sophora japonica whole extracts. Findings from isolated quercetin research should not automatically be attributed to a Sophora japonica extract or vice versa. Rutin (the primary compound in Sophora japonica flower bud extracts) has its own separate research base distinct from quercetin aglycone research.

Authoritative resources: NIH Office of Dietary Supplements | PubMed — quercetin human clinical trials

No statements on this page should be interpreted as claims that quercetin or Sophora japonica treats, prevents, or cures any disease.

Sophora japonica in AMLApure Formulations

Based on inspection of the current AMLApure catalog, quercetin is a core ingredient across the Enterinex™ product range. The following products currently list quercetin as an ingredient:

Enterinex™ 2k
A botanical enzyme formula combining nattokinase (2,000 FU), quercetin, bromelain, AMLA-derived Vitamin C, and piperine. Licorice-free formulation. Quercetin is included as a plant flavonoid studied for antioxidant and immune balance properties.

Enterinex™ Yellow — The Original
The original Enterinex™ formula combining nattokinase, quercetin, bromelain, AMLA-derived Vitamin C, piperine, licorice root, and green tea.

Enterinex™ Q
A nattokinase- and licorice-free botanical formulation centered on quercetin, bromelain, AMLA, apigenin (parsley extract), piperine, and guava (as a natural zinc source). Quercetin is a primary flavonoid component of this formula.

The inclusion of quercetin alongside bromelain and AMLA-derived Vitamin C in AMLApure formulations reflects a common botanical approach combining flavonoids, plant enzymes, and whole-food Vitamin C sources. AMLApure does not claim proven synergistic clinical outcomes from these combinations beyond what individual ingredients may support independently.

For AMLApure’s broader ingredient quality and sourcing standards, see The AMLApure Ingredient & Quality Pledge.

Related Ingredient Science

AMLA and quercetin as co-occurring polyphenols:
Quercetin occurs naturally in amla (Phyllanthus emblica) alongside emblicanins, gallic acid, ellagic acid, kaempferol, and rutin. In this sense, quercetin is part of amla’s naturally occurring polyphenol profile, distinct from the concentrated quercetin ingredient used in Enterinex™ formulations. For a full treatment of amla’s phytochemistry, see amla polyphenol and Vitamin C science — Amla Ingredient Science Library.

Nattokinase and quercetin as co-formulation ingredients:
Nattokinase and quercetin appear together in Enterinex™ 2k and Enterinex™ Yellow. Their co-inclusion reflects a multi-pathway formulation philosophy, not a claim of proven synergistic outcomes. For the science behind nattokinase, see nattokinase enzyme activity and FU research — Ingredient Science Library.

Inulin and prebiotic fiber:
AMLApure’s Glycanda™ metabolic formula takes a complementary botanical approach combining prebiotic fibers with metabolic botanicals. See inulin prebiotic fiber and gut microbiome science.

Note: Dedicated Ingredient Science pages for Bromelain, Piperine/Black Pepper, and Apigenin have not yet been published. Reciprocal links will be added when those pages are created.

Quality & Standardization

When evaluating a Sophora japonica or quercetin ingredient, the following quality and standardization parameters are relevant for professional buyers and practitioners:

  • Botanical identity: The ingredient should be sourced from authenticated Sophora japonica (Styphnolobium japonicum) plant material. Botanical identity verification is typically performed via HPTLC, HPLC, or other chromatographic methods.
  • Plant part specified: Commercial quercetin from Sophora japonica is typically derived from the flower bud. The specific plant part used should be documented in ingredient specifications and Certificates of Analysis.
  • Standardization marker: Rutin content is the primary standardization marker for Sophora japonica flower bud extracts. Quercetin ingredients derived from rutin hydrolysis should specify the quercetin aglycone content (typically expressed as a percentage, e.g., 95% quercetin) and the analytical method used.
  • Purity testing: Reputable quercetin ingredients are tested for identity, potency (flavonoid content), heavy metals, microbial contamination, and pesticide residues. Certificates of Analysis from third-party accredited laboratories provide lot-specific confirmation.

For AMLApure’s ingredient documentation approach, see The AMLApure Ingredient & Quality Pledge and the Research & Testing Library.

This page does not specify a quercetin concentration or extract ratio for AMLApure’s formulations beyond what is currently published on the respective product pages.

Safety & Considerations

Quercetin and Sophora japonica extracts are generally considered safe for most adults at typical supplemental doses. The following considerations are relevant for informed use:

  • Anticoagulants and antiplatelet medications: Quercetin has been studied in vitro for effects on platelet aggregation. Individuals taking warfarin, aspirin, or other blood-thinning agents should consult their prescribing physician before using quercetin-containing supplements.
  • Cytochrome P450 interactions: Quercetin has been shown in laboratory studies to interact with CYP3A4 and other cytochrome P450 enzymes, which may affect the metabolism of certain medications. Individuals taking prescription medications metabolized via CYP3A4 should consult a healthcare professional.
  • Thyroid medications: Some research has examined quercetin in relation to thyroid hormone metabolism. Individuals taking thyroid medications should consult their prescribing physician.
  • Immunosuppressants: Individuals on immunosuppressive therapy should consult their healthcare provider before use.
  • Pregnancy and nursing: Insufficient clinical safety data exists for high-dose quercetin supplementation during pregnancy or nursing. Consultation with a qualified healthcare professional is advised.
  • Kidney considerations: Individuals with pre-existing kidney conditions should consult a healthcare provider before using high-dose quercetin supplements.
  • Dose and duration: Most human trials have used doses in the range of 500–1,000 mg/day for several weeks. The safety profile at these doses in generally healthy adults appears acceptable based on available data. Long-term safety data at high doses in diverse populations is limited.

Never modify or discontinue prescribed medical treatment in favor of a dietary supplement without medical supervision.

This educational content is not a substitute for professional medical advice, diagnosis, or treatment.

Frequently Asked Questions

What is Sophora japonica?

Sophora japonica (now formally classified as Styphnolobium japonicum) is a tree native to China, widely cultivated across East Asia and temperate regions. Its flower buds are a commercially important source of rutin and quercetin in the supplement industry.

Is Sophora japonica a source of quercetin?

Yes — the flower buds of Sophora japonica are among the most concentrated commercial sources of rutin, which is used as a precursor to produce quercetin aglycone through a hydrolysis process. The resulting ingredient is often labeled as “quercetin from Sophora japonica.”

What is rutin?

Rutin (quercetin-3-O-rutinoside) is a naturally occurring flavonoid glycoside — quercetin bound to the sugar rutinose. It occurs in many plants including buckwheat, capers, citrus, and Sophora japonica flower buds, and has its own research base separate from quercetin aglycone.

What is the relationship between rutin and quercetin?

Quercetin is the aglycone (sugar-free) form of rutin. Rutin can be hydrolyzed to release quercetin. In commercial supplement production, rutin from Sophora japonica is often the starting material for manufacturing concentrated quercetin ingredients. They are related but structurally distinct compounds with different absorption profiles.

What are flavonoids?

Flavonoids are a large class of naturally occurring plant polyphenolic compounds found across the plant kingdom. They include several subclasses: flavonols (quercetin, kaempferol), flavones (apigenin, luteolin), flavanols (catechins), flavanones (hesperidin), anthocyanins, and isoflavones. Flavonoids are studied for antioxidant activity and a wide range of cellular and nutritional properties.

What is quercetin?

Quercetin is a naturally occurring flavonol found in many plant foods including capers, onions, apples, broccoli, berries, and green tea. It is one of the most studied dietary polyphenols in nutritional science, examined for antioxidant, immune-related, and other cellular properties.

What foods contain quercetin?

Quercetin is found in many commonly consumed plant foods. The highest concentrations are typically found in capers, red and yellow onions, apples (particularly the skin), broccoli, elderberries, blueberries, and green tea. It also occurs naturally in amla (Phyllanthus emblica) as part of its polyphenol profile.

Why is Sophora japonica used in supplements?

Sophora japonica flower bud extract is used as a commercial source of rutin and quercetin because it provides a highly concentrated, consistent, and well-characterized source of these flavonoids at commercial scale with defined standardization potential.

Is Sophora japonica the same as quercetin?

No. Sophora japonica is the plant; quercetin is the flavonoid compound. Sophora japonica flower bud extract is one source from which quercetin can be derived, but quercetin is also found in many other plants and foods. A Sophora japonica extract may be standardized for rutin content, quercetin content, or total flavonoids depending on the manufacturing specification.

References & Further Reading

  • Serban MC, et al. Effects of quercetin on blood pressure: a systematic review and meta-analysis of randomized controlled trials. J Am Heart Assoc. 2016;5(7):e002713. PubMed
  • Boots AW, Haenen GR, Bast A. Health effects of quercetin: from antioxidant to nutraceutical. Eur J Pharmacol. 2008;585(2–3):325–337. PubMed
  • Harwood M, et al. A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity. Food Chem Toxicol. 2007;45(11):2179–2205. PubMed
  • Russo M, et al. The flavonoid quercetin in disease prevention and therapy: facts and fancies. Biochem Pharmacol. 2012;83(1):6–15. PubMed
  • European Food Safety Authority. Scientific opinion on the safety of quercetin as a novel food ingredient. EFSA Journal. 2010;8(7):1640. EFSA
  • NIH Office of Dietary Supplements — Dietary Supplements overview
  • PubMed: quercetin human clinical trials
  • PubMed: Sophora japonica flavonoid research

This page is part of the AMLApure Ingredient Science Library. Content is educational and does not constitute medical advice. These statements have not been evaluated by the FDA. AMLApure products are not intended to diagnose, treat, cure, or prevent any disease.