IngredientesQuercetin is a plant flavonol from the flavonoid group of polyphenols. Its name derives from the Latin word quercetum, meaning "oak forest," and it belongs to the flavonol category. The IUPAC name is 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one, and its molecular formula is C15H10O7. An alternative systematic name is 3,3′,4′,5,7-pentahydroxyflavone, which reflects the five hydroxyl substituents on the core chromenone scaffold. The name has been applied since 1857. Quercetin is a flavonoid compound widely present in plants and exhibits a variety of biological activities.
Despite having five hydroxyl groups, quercetin is lipophilic by nature, which results in limited bioavailability. Quercetin has a relatively large resonance structure in chemical terms and exhibits a yellow color-imparting ability, antioxidation activity, vitamin-P activity, and ultraviolet-absorbing activity. Quercetin is soluble in readily water-soluble organic solvents but insoluble or scarcely soluble in water, which renders handling difficult.
Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin (also known as quercetin-3-O-rutinoside) and quercitrin, found in citrus fruit, buckwheat, and onions. In 1930, rutin (quercetin-3-O-rutinoside), one of quercetin's most common forms, was isolated from oranges, and it was initially believed to be a vitamin; for a while, rutin was called vitamin P. Isoquercetin shares the same aglycone as rutin and quercitrin: quercetin. It has been shown that quercetin-containing glycosides liberate quercetin in the intestinal tract; therefore, it is justified to assume that all the pharmacological properties of quercetin are also shared by isoquercetin and rutin when administered orally.
Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it. A broad list of food sources includes capers, lovage, sorrel, radish leaves, carob fiber, dill, cilantro, Hungarian wax pepper, fennel leaves, red onion, radicchio, watercress, buckwheat, kale, chokeberry, cranberry, lingonberry, black plums, cowpeas, sweet potato, blueberry, sea buckthorn berry, rowanberry, crowberry, prickly pear cactus fruits, red apples, broccoli, bilberry, tomatoes, black tea, and green tea.
Quercetin is one of the most abundant dietary flavonoids, with an average daily consumption of 25–50 mg. In red onions, higher concentrations of quercetin occur in the outermost rings and in the part closest to the root, the latter being the part of the plant with the highest concentration. One study found that organically grown tomatoes had 79% more quercetin than non-organically grown fruit. Quercetin is also present in various kinds of honey from different plant sources. Flavonoids in propolis—the resinous material produced by bees—are mainly composed of flavonol aglycones such as quercetin, which are considered a major effective component of propolis.
In plants, phenylalanine is converted to 4-coumaroyl-CoA in a series of steps known as the general phenylpropanoid pathway using phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumaroyl-CoA-ligase. One molecule of 4-coumaroyl-CoA is added to three molecules of malonyl-CoA to form tetrahydroxychalcone. Tetrahydroxychalcone is then converted into naringenin using chalcone isomerase. Naringenin is converted into eriodictyol using flavonoid 3′-hydroxylase. Eriodictyol is then converted into dihydroquercetin with flavanone 3-hydroxylase, which is then converted into quercetin using flavonol synthase.
Quercetin has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods. In supplemental form, it is most commonly available as the aglycone (the "free" compound without attached sugars), but multiple enhanced-bioavailability formulations have been developed for commercial use. One delivery system based on food-grade lecithin — known as Quercetin Phytosome — was developed to improve solubility. This formulation leads to a significant improvement in quercetin bioavailability when administered to human volunteers. Other approaches include quercetin-loaded nanoparticles and self-emulsifying hydrogel systems. Quercetin, a dietary flavonoid typically consumed as a glycoside in food, is available in supplements in its aglycone form. This aglycone form is the most studied in preclinical and clinical research because of its antioxidant, anti-inflammatory, and metabolic properties.
Many medicinal herbs used in traditional medicines such as Ayurveda, Kampo, Unani, Traditional Chinese Medicine (TCM), and Native American traditions contain quercetin. In each of these systems, the compound was not isolated but consumed as part of complex plant preparations, and its effects were understood through the lens of traditional frameworks rather than biochemical analysis.
Quercetin has a long history of use in traditional Chinese medicine, showing a capacity to induce anti-inflammatory and antioxidant effects. In TCM, quercetin is known to give Sophora japonica (槐花, Huaihua), Ginkgo biloba (银杏, Yinxing), Scutellaria baicalensis (黄芩, Huangqin), and Morus alba (桑白皮, Sangbaipi) many of their healing properties. Over the years, classical formulas such as Huangqin Tang (黄芩汤) and Yinxingye Pian (银杏叶片) have included these herbs to help with problems like inflammation, heart diseases, and mental disorders. The ability of these TCM preparations to ease symptoms is attributed to their quercetin content, which reflects the longstanding use of quercetin-rich herbs in the treatment of chronic illnesses.
The traditional uses of quercetin-rich herbs in TCM are well matched by experimental results showing that these plant extracts reduce toxicity, dampen inflammation, and support organs such as the liver and lungs. Quercetin is widely used in botanical medicine and traditional Chinese medicine due to its potent antioxidant activity.
Quercetin is the major polyphenolic flavonoid found in food products, including berries, apples, cauliflower, tea, cabbage, nuts, and onions, that have traditionally been treated as anticancer and antiviral remedies, and used for the treatment of allergic, metabolic, and inflammatory disorders, eye and cardiovascular diseases, and arthritis. Many of these applications in folk medicine corresponded to the functional roles that quercetin is now understood to play biochemically, though the specific compound was not identified until the mid-19th century. Quercetin has been classified as a cognitive enhancer in traditional and oriental medicine.
Investigation of the chemical structure of quercetin has found that there are four hydroxyl groups on the benzo-dihydropyran ring of the polyphenol, so quercetin has a strong antioxidant capacity, can eliminate free radicals produced in the body, and can help the body maintain a stable state. The C-3 hydroxyl group on the flavonol ring is particularly significant because it permits chelation of pro-oxidant metal ions including iron and copper. Quercetin is renowned for its potent antioxidant properties. It scavenges free radicals and chelates metal ions, thus protecting cells from oxidative stress.
In vivo, quercetin undergoes extensive first-pass metabolism. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. These conjugates include quercetin-3′-sulfate, quercetin-3-glucuronide, and isorhamnetin (a methylated metabolite). Quercetin and its metabolites (quercetin-3′-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and CYP3A4, while they did not affect CYP2D6 activity. Rutin, the O-glycoside of quercetin, further contributes by generating aglycone metabolites through gut microbiota activity, replicating quercetin's metabolic enzyme inhibition and antioxidant actions.
Quercetin is a bioactive compound widely used in botanical medicine and traditional Chinese medicine due to its potent antioxidant activity. In recent years, antioxidant activities of quercetin have been studied extensively, including its effects on glutathione (GSH), enzymatic activity, signal transduction pathways, and reactive oxygen species (ROS) caused by environmental and toxicological factors.
Quercetin interacts with NADPH oxidase, which can result in changes in reactive oxygen species levels. Elevated ROS levels can activate the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, which subsequently promotes the expression of antioxidant genes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx). As a result, the antioxidant response is potentiated, reducing oxidative stress and protecting cells from damage. Quercetin has been found to be the most effective free radical scavenger in the flavonoid family.
Quercetin has been extensively studied for its anti-inflammatory properties, where it alleviates the inflammatory response by inhibiting the NF-κB and MAPK signaling pathways. One of the important mechanisms of quercetin's action at the molecular level is the reduction in pro-inflammatory cytokine activity, such as IL-6, IL-17, TNF-α, and IL-1β, by blocking NF-κB and AMPK signaling pathways.
This flavonoid inhibits the activity of cyclooxygenase (COX-2) and lipoxygenase, which limits the synthesis of inflammatory mediators such as prostaglandins and leukotrienes. In addition, it reduces the activity of inducible nitric oxide synthase (iNOS), which leads to reduced levels of nitric oxide. Quercetin targets inflammation by modulating the expression of cytokines and pro-inflammatory molecules and by inhibiting pro-inflammatory enzymes.
Research has demonstrated that quercetin inhibits signaling pathways related to the inflammatory process, including phosphorylation of mitogen-activated protein kinases (MAPKs), inhibitor of nuclear factor κ-B kinase (IKK)α/β, c-Jun, cAMP response element-binding protein (CREB), activating transcription factor 2 (ATF2) and nuclear factor (NF)-κB p65, and blocks the translocation of NF-κB p65 into the nucleus.
Unlike pharmaceutical antihistamines, which work by blocking histamine receptors, quercetin prevents mast cells from releasing histamine in the first place. A study compared quercetin to cromolyn sodium — a pharmaceutical mast cell stabilizer — using cultured human mast cells. Quercetin inhibited histamine secretion by 82–87%, compared to 67% for cromolyn. It also showed greater suppression of IL-8 and TNF cytokine release. These results are primarily from in vitro work, and the clinical relevance in humans requires further large-scale confirmation.
Quercetin has been reported to stimulate glucose uptake in cultured skeletal muscle through an insulin-independent mechanism involving AMPK, a key regulator of whole body-energy homeostasis. Treatment with quercetin stimulated AMPK and increased GLUT4 translocation and protein content in cultured rat skeletal muscle cells, as well as hepatic AMPK activation in hepatocytes.
Senolytics, including the combination of dasatinib and quercetin (D+Q), selectively eliminate senescent cells by transiently disabling pro-survival networks that defend them against their own apoptotic environment. Quercetin, a dietary flavonoid, was first documented to exert senolytic activity against senescent human endothelial cells and mouse bone marrow-derived mesenchymal stem cells. One of the first senolytic drugs to be identified was quercetin, a natural flavonoid ubiquitously present in fruits, vegetables, nuts, tea, and red wine.
Quercetin can improve the antioxidant enzyme activity of inflammatory macrophages and inhibit their ROS production and overexpression of inflammatory factors. Additionally, quercetin upregulates mitochondrial membrane potential, ATP production, and ATP synthase content when these are reduced by inflammatory stimuli, and reverses mitochondrial morphology damage to a certain extent. Quercetin was also found to significantly upregulate the protein expressions of SIRT1 and PGC-1α. Quercetin has been found to modulate inflammatory processes through a variety of signaling pathways, including the phosphatidylinositol-3-phosphate kinase (PI3K)/Akt signaling pathway.
Evidence strength: Moderate — multiple RCTs and meta-analyses; clinically modest effect sizes.
Quercetin, the most abundant dietary flavonol, has antioxidant effects in cardiovascular disease, but the evidence regarding its effects on blood pressure (BP) has not been conclusive; its impact on BP has been assessed through a systematic review and meta-analysis of available randomized controlled trials. Overall, the impact of quercetin on BP was reported in 7 trials comprising 9 treatment arms (587 patients). The results of the meta-analysis showed significant reductions both in systolic BP (WMD: −3.04 mm Hg, 95% CI: −5.75, −0.33, P=0.028) and diastolic BP (WMD: −2.63 mm Hg).
A separate, more recent meta-analysis in Nutrition Reviews corroborated these findings. Pooled results showed that quercetin significantly lowered both systolic BP (WMD, −3.09 mmHg; 95% CI, −4.59 to −1.59; P = 0.0001) and diastolic BP (WMD, −2.86 mmHg; 95% CI, −5.09 to −0.63; P = 0.01).
A meta-analysis of 20 RCTs examining metabolic syndrome components found that altogether 20 studies with a total sample size of 1,164 subjects were included in the analysis. A pooled analysis showed that quercetin consumption led to a significant reduction in fasting blood glucose (WMD: −1.03 mg/dL; 95% CI: −1.87 to −0.19), and systolic blood pressure (WMD: −1.96 mmHg; 95% CI: −3.11 to −0.81). However, there were no significant effects on triglycerides, HDL-C, waist circumference, and diastolic blood pressure.
A specific RCT in patients with borderline hypertension found that 162 mg of quercetin daily for 6 weeks reduced 24-hour ambulatory systolic blood pressure by 3.6 mmHg compared to placebo. This study was notable for using ambulatory blood pressure monitoring — the gold standard for blood pressure assessment — rather than single office measurements.
The results indicate that quercetin supplementation notably lowers systolic blood pressure in hypertensive and normotensive individuals, but its impact on diastolic blood pressure is insignificant. These findings hint at quercetin's potential as an auxiliary treatment for systolic hypertension, with a need for more high-quality, randomized controlled trials to determine optimal dosage and duration.
Evidence strength: Mixed and inconsistent in human trials.
Experimental studies including both in vitro methods and in vivo animal models mainly outline the following effects of quercetin: antihypertensive, hypolipidemic, hypoglycemic, anti-atherosclerotic, and cardioprotective effects. From the clinical point of view, there are human studies and meta-analyses implicating its beneficial effects on glycemic and lipid parameters. In contrast, other human studies failed to demonstrate consistent favorable effects of quercetin on other cardiometabolic risk factors such as metabolic syndrome, obesity, and hypertension.
A double-blind, randomized clinical trial was carried out for 10 weeks on 72 women who were given 500 mg of quercetin daily. Quercetin significantly decreased tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), high-density lipoprotein cholesterol (HDL-C), and systolic blood pressure (SBP), while LDL-C, total cholesterol, and triglycerides (TG) were not significantly reduced. The results showed that quercetin supplementation did not affect cardiovascular risk factors overall.
In another study, healthy candidates with 4.0–7.2 mmol/L cholesterol levels were administered 1 g quercetin daily for 28 days. There was no alteration in the cardiovascular risk factors, including HDL, LDL, and triglyceride levels.
Significant drawbacks in the clinical trials' design were identified, while the absence of pharmacokinetic/pharmacodynamic tests prior to the studies attenuated the power of clinical results. Additional well-designed preclinical and clinical studies are required to examine the therapeutic mechanisms and clinical efficacy of quercetin in cardiovascular diseases.
Evidence strength: Preliminary in humans; well-characterized mechanism in vitro and in animal studies.
There is much evidence that quercetin exerts anti-allergic effects in both human and experimental animal models of allergic diseases. The primary mechanism, demonstrated in cell-based research, is mast cell stabilization. A small human pilot arm (10 volunteers) in one study found significant reduction in contact dermatitis. These are in vitro and small-sample results, not large clinical trials, but the mechanism is well-established.
A 2016 study in Inflammation Research found that quercetin inhibited the activation of mast cells and their release of inflammatory cytokines. A double-blind pilot study in humans with seasonal allergies demonstrated that quercetin supplementation reduced nasal and eye symptoms significantly. Large, adequately powered, placebo-controlled trials specifically in allergic rhinitis populations remain limited.
Evidence strength: Moderate — systematic review and meta-analysis of RCTs, but studies are small and heterogeneous.
After application of inclusion and exclusion criteria, 13 studies with a total of 249 sedentary to well-trained participants were included in a systematic review and meta-analysis. For all studies there were some concerns about the risk of bias. All but one study used a supplementation dosage of 1,000 mg/day. Quercetin supplementation accelerated recovery of muscle function and significantly decreased muscle soreness 0/24 h after exercise (SMD: −1.33; p = 0.03), creatine kinase levels 24/48 h after exercise (SMD: −1.15; p = 0.02), and post-exercise oxidative stress (SMD: −0.92; p = 0.03). However, quercetin supplementation had no effect on IL-6 concentration.
Evidence strength: Preliminary — one small RCT with positive results; no large trials.
In a prospective, randomized, double-blind, placebo-controlled trial of quercetin in men with chronic prostatitis, 20% of patients taking a placebo and 67% of patients taking quercetin had an improvement of symptoms of at least 25% as measured by the NIH chronic prostatitis symptom score. In an unblinded open-label follow-up study, 82% of patients who received a formulation of quercetin, bromelain, papain, and zinc had at least a 25% improvement in symptom score. The open-label extension and combination formula used in the follow-up study limit the conclusions that can be drawn about quercetin alone.
Evidence strength: Early-phase clinical trials; mechanism established in preclinical work; human outcome data emerging but not yet definitive.
In the first clinical trial of senolytics, the dasatinib and quercetin combination improved physical function in patients with idiopathic pulmonary fibrosis (IPF), a fatal senescence-associated disease. The first human studies showed a reduced senescent cell burden in the adipose tissue of patients suffering from diabetic kidney disease and improved physical functions in patients with idiopathic pulmonary fibrosis.
A randomized controlled trial examined 60 healthy women past menopause who intermittently received a senolytic combination of dasatinib and quercetin. So far the only senolytic therapy demonstrated in clinical trials to clear senescent cells in humans as well as it does in mice is the dasatinib and quercetin combination. Clinical research groups presently running human studies are still in the process of figuring out dosing and optimal use cases for the various first-generation small molecule senolytics, such as dasatinib and quercetin. Initial results from a Mayo Clinic phase 2 study in older women with osteoporosis are described as quite positive, despite the failure to produce a significant difference when considering the whole treatment group.
It is important to note that in senolytic protocols, quercetin has been studied in combination with dasatinib (a prescription tyrosine kinase inhibitor), not as a stand-alone agent. Emerging research suggests that the senolytic regimen of dasatinib+quercetin reduces senescent cells, potentially mitigating age-related health and cognitive decline. Pilot studies aim to assess the feasibility and safety of D+Q in older adults with various conditions. The senolytic applications of quercetin as a standalone supplement in humans remain unproven by clinical trial standards.
Evidence strength: Preliminary to moderate; meta-analytic support for fasting glucose reduction but effect sizes are small.
A systematic review and meta-analysis of RCTs evaluated the effects of quercetin on metabolic syndrome components such as waist circumference, systolic blood pressure, diastolic blood pressure, fasting blood glucose, triglyceride, and HDL-C. A systematic literature search up to December 2023 was completed, identifying 20 studies with a total sample size of 1,164 subjects. A pooled analysis showed that quercetin consumption led to a significant reduction in fasting blood glucose (WMD: −1.03 mg/dL; 95% CI: −1.87 to −0.19), and systolic blood pressure.
Evidence strength: Preclinical only for most indications; no approved clinical use.
Quercetin is one of the most important plant molecules that has shown many pharmacological activities, including anticancer, antiviral, and treating allergic, metabolic, and inflammatory disorders. It has shown a wide range of anticancer properties, and several reports indicate its efficacy as a cancer-preventing agent. The antiproliferative and antimutagenic activities in vitro have made it a candidate for clinical trials in cancer therapy. However, at the time of writing, no clinical evidence from completed phase III trials supports quercetin as an approved cancer therapy. The evidence base remains primarily in vitro and in animal models.
Evidence strength: Predominantly preclinical; human data very limited.
Quercetin has already been shown to be able to improve learning and memory ability, and to be a potential novel therapeutic strategy against Alzheimer's disease. Using rat hippocampal cultures, researchers have been capable of delivering encapsulated quercetin, protecting neuronal cultures from oxidative stress and hypothesizing its use against Alzheimer's disease or other neurodegenerative disorders. Quercetin and other polyphenols were used in a study to protect brain mitochondria from amyloid fragment fibrillogenesis. Quercetin was able to destabilize amyloid aggregates, thereby inhibiting the fibrillation process and rescuing the mitochondrial function. These findings are from animal and cell models, and well-designed human clinical trials are needed before clinical conclusions can be drawn.
Quercetin is a lipophilic compound that is absorbed by simple diffusion and involves both oral and intestinal bacteria for its enzymatic hydrolysis. Quercetin is relatively lipophilic with low solubility in water. Quercetin glucoside is more water-soluble than the aglycone, and its absorption is limited to sodium-dependent glucose transporter-1 (SGLT-1); however, glucose transporter-2 (GLUT-2)-dependent absorption is also a significant contributor.
Unformulated standard quercetin provides a Cmax of only 14 ng/mL, and no quercetin or quercetin metabolites were detected after 5 h of consumption in some pharmacokinetic studies. Various formulation strategies have been developed to overcome this limitation. A delivery system based on food-grade lecithin — Quercetin Phytosome — was developed, and its solubility was shown to be considerably higher than that of unformulated quercetin, leading to a significant improvement in quercetin bioavailability when administered to human volunteers in a clinical study.
The intake of quercetin together with a meal could improve absorption notably — as a greater surface area promotes dissolution in the intestinal lumen and thus bioavailability. Dietary fat compounds can greatly contribute to quercetin's bioavailability and may even boost the effects of carrier systems by enhancing micellization.
The overall lack of in vivo toxicity of quercetin is consistent with its known metabolic fate; specifically, its extensive microbial degradation in the gastrointestinal tract of both animals and humans, followed by methylation, oxidation and conjugative metabolic processes that occur in the liver and kidneys and eventual elimination through the bile, feces, and urine. The role of intestinal microbiota in the bioavailability and physiological function of dietary polyphenols such as quercetin has been increasingly discussed.
The following dosages are reported as used in cited scientific studies and clinical trials; they are not prescriptive recommendations:
Several clinical trials have demonstrated the benefits of quercetin for enzymatic, metabolic and cardiovascular health; however, approximately 60% of these studies fail to verify the actual concentration administered, generating uncertainty about their findings. Additionally, when five commercial brands were tested, only one contained the amount labeled; three contained approximately 80%, and one contained merely 14.8% of the stated dose. This highlights a quality-control issue that affects the interpretation of real-world outcomes.
Published and unpublished information supports the safety of quercetin including ADME studies; acute, subchronic, and chronic toxicity studies; carcinogenicity, genotoxicity, and reproductive/developmental toxicity studies; pharmacokinetic studies; and human clinical and epidemiological studies. From all of the available toxicology studies in multiple species, there is an apparent lack of significant adverse systemic toxicity.
A two-year toxicity and carcinogenicity study in rats by the National Toxicology Program (NTP) was pivotal in establishing safety; the no-observed adverse effect level for this study was approximately 2,200 mg/kg body weight per day (the highest dose tested). The weight-of-the-evidence from toxicological safety studies and human clinical studies corroborating epidemiological studies, together with recent human pharmacokinetic studies, demonstrates that quercetin is safe for intended use as a supplement. Based on information provided to FDA, the agency accepted the conclusion that quercetin is generally recognized as safe (GRAS) under the intended conditions of use.
No significant differences were observed between quercetin formulation treatments and control in vital signs, physical examination results, or ECG results, demonstrating the new formulation is safe and well tolerated, and is as safe as unformulated quercetin.
In a clinical trial reporting adverse events out of 30 patients enrolled, adverse events in the quercetin arm included one patient who developed a headache after the first few doses (which resolved) and one patient who noted mild tingling of the extremities after each dose. Adverse effects that have been listed in monographs include emesis, dyspnea, and nephrotoxicity; however, the nephrotoxicity has not been substantiated in recent reports, and several studies involve use of quercetin for its anti-oxidative and anti-apoptotic effects in kidney disease models.
Quercetin interacts with cytochrome P450 enzymes and drug transporters at pharmacological doses, creating the potential for herb–drug interactions. In studies, the inhibitory effects of quercetin and its metabolites were tested on CYP2C19, CYP3A4, and CYP2D6 enzymes as well as on organic anion-transporting polypeptides (OATPs) and ABC transporters (BCRP and MRP2). Most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. These data demonstrate that not only quercetin but some of its conjugates can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.
Clinical trial protocols flag caution for pregnant and/or breastfeeding women and individuals with kidney problems. These cautions reflect the absence of controlled safety data in these populations rather than confirmed harm from human studies at standard doses.
Condiciones de salud que quercetina puede ayudar a apoyar.
Quercetin inhibits mast cell degranulation and suppresses histamine release, directly addressing IgE-mediated respiratory allergic responses. In vitro and murine allergic rhinitis models consistently show reduced sneezing, nasal congestion, and Th2 cytokine levels. Two small clinical trials using bioavailable formulations (including a nutraceutical with quercetin, Perilla, and vitamin D3) showed significantly superior symptom improvement over antihistamine monotherapy in grass-pollen allergic rhinitis patients. Typical clinical dosing is 500–1000 mg/day.
Quercetin is identified in multiple peer-reviewed experimental reviews as a phytochemical with anti-ALS activity. It has been explored computationally and experimentally as a potential ALS therapeutic. A 2024 in vivo study demonstrated that rutin (quercetin-3-rutinoside) reduced SOD1 aggregation and neuroinflammation, improved motor function in ALS mice, supporting the broader quercetin class. Evidence is primarily preclinical.
Quercetin, a dietary flavonoid, supports antioxidant defense through direct free-radical scavenging and by activating the Nrf2 signaling pathway, which upregulates endogenous antioxidant enzymes such as SOD, catalase, and glutathione. Human and clinical evidence—including randomized controlled trials—documents improvements in total antioxidant capacity and oxidative stress biomarkers, though effect sizes are variable and some trials report null findings, particularly in healthy populations. The evidence is strongest in populations under metabolic or oxidative stress (e.g., type 2 diabetes).
Quercetin is a flavonoid with documented anti-atherosclerotic, antihypertensive, and endothelial-protective effects. A 2021 PMC review showed quercetin mitigates endothelial dysfunction by addressing hypertension, atherosclerosis, and senescent endothelial cells. Clinical data indicate modest blood pressure reduction (3–7 mmHg) and improved FMD.
A randomized, double-blind, placebo-controlled trial in 50 women with rheumatoid arthritis found that 500 mg/day quercetin for 8 weeks significantly reduced morning stiffness, pain scores, disease activity (DAS-28), and plasma TNF-α compared to placebo. Mechanistic studies show quercetin inhibits NF-κB and suppresses pro-inflammatory cytokines including IL-1β, IL-6, and TNF-α in joint tissue. Evidence for osteoarthritis is less robust, relying mainly on preclinical and animal data.
Quercetin is a flavonoid that stabilizes mast cells, inhibits histamine release, and suppresses Th2-mediated inflammatory pathways relevant to asthma. Epidemiological studies link higher quercetin intake to lower asthma incidence. It inhibits 5-lipoxygenase and phosphodiesterase activities, reducing leukotriene synthesis and promoting bronchodilation-relevant cAMP elevation.
Quercetin is a flavonoid with antioxidant and anti-inflammatory properties studied for improving aerobic exercise performance and reducing exercise-induced oxidative stress. A meta-analysis found quercetin supplementation produces a small but significant improvement in maximal oxygen uptake (VO2 max) and endurance performance.
Quercetin, a dietary flavonoid, has been shown to attenuate rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and systemic lupus erythematosus in human and animal studies. It exerts anti-inflammatory, antioxidant, and neuroprotective actions. A 2021 review in Frontiers in Immunology summarized its pharmacological applications across multiple autoimmune diseases.
Quercetin is a bioflavonoid with potent anti-inflammatory and antihistamine properties directly relevant to alleviating insect bite and sting symptoms. EBSCO Research Starters on natural treatments for insect bites lists quercetin as a proposed natural treatment that may help reduce bite and sting symptoms by reducing histamine-mediated reactions.
Quercetin, a natural flavonoid, has clinical evidence supporting its use for interstitial cystitis/bladder pain syndrome (IC/BPS). An open-label trial found 500 mg twice daily for 4 weeks reduced IC symptom scores by approximately half. Quercetin acts via mast cell stabilization, anti-inflammatory, and antioxidant mechanisms relevant to bladder wall pathology.
Quercetin and its metabolites (isorhamnetin, tamarixetin) potently inhibit platelet aggregation, suppress granule secretion, and reduce integrin αIIbβ3 function. Isoquercetin inhibited thrombosis in a murine laser-injury model. Quercetin synergistically enhances aspirin's antiplatelet effects, reducing aspirin IC50 by an order of magnitude.
Quercetin, a ubiquitous dietary flavonoid, has been assessed in multiple RCTs and meta-analyses for blood pressure reduction, with significant effects in hypertensive individuals at doses of 500–1,000 mg/day. Mechanisms include inhibition of ACE, reduction of oxidative stress, and improvement of endothelial function.
Quercetin is a widely distributed flavonol with documented antidiabetic activity in preclinical studies and some clinical trials. It inhibits alpha-glucosidase, stimulates insulin secretion, and improves insulin resistance. Meta-analyses of RCTs show quercetin supplementation significantly reduces fasting blood glucose in T2DM patients.
Quercetin is specifically included in the 2025 Frontiers in Pharmacology PROSPERO-registered systematic review on chronic bronchitis. A preclinical study showed quercetin at 0.05–0.1 g/kg for 5 days reduced cough frequency comparably to pentoxyverine citrate in bronchitis models. It also suppresses mucin expression, a hallmark of chronic bronchitis.
Quercetin is cited by Liv Hospital for bursitis management due to its anti-inflammatory and antioxidant properties. It inhibits NF-κB and reduces inflammatory cytokine production. A network meta-analysis found quercetin more effective than placebo in reducing VAS pain scores in RA. It is included among the strongest-evidence anti-inflammatory supplements.
Quercetin has anti-inflammatory properties and has been studied as part of a multi-ingredient supplement for early CTS alongside bromelain, ALCAR, ALA, and B vitamins. The combination produced statistically significant improvement in nerve function and sleep quality vs. physical therapy alone. Bromelain enhances quercetin's bioavailability and they are often studied together.
Quercetin is a flavonol that inhibits NF-κB, COX-2, and multiple inflammatory mediators implicated in cartilage degradation. Multiple in vitro studies confirm quercetin reduces IL-1β–induced MMP expression and chondrocyte apoptosis. A 2021 pilot RCT (n=72 OA patients, 8 weeks) found 500 mg/day quercetin significantly reduced serum IL-6, hsCRP, and WOMAC pain scores vs. placebo. It is recognized in OA nutraceutical reviews for its chondroprotective potential.
Quercetin is a flavonoid with well-documented mast cell-stabilizing and anti-histamine properties. It inhibits IgE-mediated mast cell degranulation, reduces histamine, IL-4, IL-5, TNF-α, and eosinophil infiltration in preclinical models. A 2025 systematic review and meta-analysis of preclinical studies found it significantly reduces IgE, OVA-specific IgE, histamine, and inflammatory cytokines. A pediatric RCT (PMC, 2025) used quercetin as part of a nutraceutical add-on in seasonal allergic rhinitis in children, showing symptom reduction. Human clinical data remain limited but direction-consistent.
Multiple human RCTs and meta-analyses have examined quercetin's effect on lipid profiles, with results that are mixed but documented. One meta-analysis found significant reductions in HDL-C and triglycerides after 8 or more weeks of supplementation in parallel-design trials. An earlier meta-analysis found only a significant reduction in triglycerides at doses above 50 mg/day, with no clinically relevant effect on total cholesterol or LDL. Mechanistically, quercetin suppresses lipid aggregation and reduces LDL oxidation.
Quercetin is a flavonoid with documented effects on mitochondrial biogenesis and anti-fatigue activity. Multiple clinical trials show quercetin supplementation reduces exercise-induced fatigue and improves endurance performance. It activates SIRT1 and PGC-1α to stimulate mitochondrial biogenesis—a key anti-fatigue mechanism.
Quercetin, a dietary flavonoid, has demonstrated anti-inflammatory activity across cell, animal, and human studies, primarily by suppressing NF-κB signaling and reducing pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, CRP). A meta-analysis of randomized controlled trials found significant reductions in circulating CRP and IL-6 specifically in participants with diagnosed diseases, though no broad effect was seen across all populations. Evidence strength is moderate: preclinical data are robust, but human RCTs are limited in number, sample size, and duration, and bioavailability remains a key variable.
Quercetin is a polyphenolic flavonoid with anti-inflammatory and antioxidant properties that reduce chronic pain-related inflammation. It inhibits NF-κB, COX-2, and lipoxygenase pathways and reduces histamine-mediated pain sensitization. Evidence supports its role in reducing inflammation associated with arthritis and other chronic pain conditions.
Quercetin is a flavonol present in onions, apples, and many plants with documented circulatory benefits including blood pressure reduction, improved endothelial function via NO upregulation, anti-platelet effects, and reduction of vascular inflammation. A meta-analysis of RCTs found quercetin supplementation (>500 mg/day) significantly reduced systolic blood pressure. It is among the most studied flavonoids for vascular health.
Quercetin, a flavonoid found widely in fruits and vegetables, has demonstrated neuroprotective effects through multiple mechanisms including antioxidant activity, anti-neuroinflammation, and inhibition of amyloid-beta aggregation — primarily in preclinical (cell and animal) studies. A 40-week randomized, double-blind, placebo-controlled human trial found that 110 mg/day of quercetin glycosides improved reaction time and preserved cerebral blood flow in older adults with age-related memory decline. However, at least one separate human RCT (12 weeks, queried general community sample) found no significant cognitive benefit, and the overall human evidence base remains limited, with several ongoing early-phase clinical trials.
Quercetin is a flavonoid with documented anti-influenza and antiviral mechanisms and clinical evidence for reducing upper respiratory infection incidence in athletes. A double-blind RCT found quercetin (1000 mg/day) significantly reduced URTI incidence from 45% to 5% vs. placebo in endurance athletes. It inhibits influenza neuraminidase and blocks viral replication. A 2020 meta-analysis confirmed quercetin reduces URTI duration and severity.
Quercetin demonstrates significant anti-HSV-1 activity in vitro via suppression of TLR-3-dependent inflammatory signaling and inhibition of HSV proteins (gD, ICP0) and viral genes (ICP0, UL13, UL52). It is identified as an AMPK activator with anti-HSV activity similar to resveratrol in cell culture. Evidence is primarily in vitro; no large clinical trials specific to herpes labialis have been published.
Quercetin, a flavonoid with potent anti-inflammatory and antioxidant properties, has been investigated in preclinical and clinical contexts for ulcerative colitis. It modulates NF-κB, reshapes gut microbiota, and restores tryptophan metabolism to support intestinal barrier integrity. It is included in polyphenol meta-analyses showing benefit in UC.
Quercetin is a dietary flavonoid under clinical investigation for COPD. Preclinical studies show it prevents progression of COPD-like lung disease in mice by inhibiting MMP expression and rhinovirus replication. A safety RCT (BMJ Open Respiratory Research, 2020) established its tolerability in COPD patients. Phase II efficacy trials are ongoing. Definitive clinical efficacy has not yet been established.
Quercetin is a flavonoid with documented tyrosinase-inhibiting and antioxidant properties relevant to periorbital hyperpigmentation. It suppresses melanogenesis by inhibiting tyrosinase and MITF, and is listed among bioactive compounds studied in the context of skin hyperpigmentation management in authoritative scientific literature.
Quercetin has clinical and preclinical evidence for dermatitis. In 10 nickel-sensitive volunteers, oral quercetin (2 g/day for 3 days) reduced nickel-induced contact dermatitis reactions, with 8/10 subjects achieving ≥50% reduction. Animal studies confirm anti-AD activity, and proteomics research is actively investigating its mechanisms in atopic dermatitis.
Quercetin is a polyphenol with antioxidant and anti-inflammatory properties identified in recent evidence reviews as potentially beneficial in diverticular disease. A 2025 narrative review specifically addressing polyphenols in diverticular disease highlighted quercetin among key compounds that may protect intestinal integrity, modulate gut microbiota, and reduce oxidative stress characteristic of diverticular disease pathophysiology.
Quercetin has antihistamine-like and anti-inflammatory properties mechanistically relevant to eczema, inhibiting mast cell activation, IgE-mediated responses, and histamine release. Multiple eczema evidence databases rate quercetin as a complement to first-line eczema treatments based on its documented antiallergic mechanism, though large-scale clinical RCTs specifically for eczema are limited.
Quercetin is a polyphenol flavonoid with anti-inflammatory, antioxidant, and anti-estrogenic properties studied in endometriosis. A single RCT found that 200 mg quercetin daily significantly reduced dysmenorrhea, chronic pelvic pain, and dyspareunia compared to placebo. It also inhibits aromatase, potentially reducing local estrogen production in ectopic endometrial tissue.
Quercetin is a flavonoid antioxidant that activates the Nrf2/HO-1 antioxidant pathway in testicular tissue, chelates heavy metals, and protects sperm from oxidative stress-induced DNA damage. Animal studies consistently demonstrate protection of sperm parameters from multiple toxic insults. Clinical combination supplement evidence and inclusion in evidence-reviewed fertility protocols supports its relevance to male fertility.
Quercetin is a flavonoid with well-documented mast cell-stabilizing and anti-histamine properties. It inhibits IgE-mediated degranulation, reduces pro-inflammatory cytokines (IL-4, IL-5), and modulates Th1/Th2 immune balance. Two clinical trials using quercetin monotherapy reported symptom reduction and improved quality of life in allergic disease patients. Preclinical evidence also supports its benefit in food allergy models.
Quercetin is a flavonoid that stabilizes mast cells, reduces histamine release, inhibits tryptase, and supports gut barrier integrity. These properties make it directly relevant to food sensitivity involving histamine intolerance, IgG-mediated reactions, and increased intestinal permeability. It is widely used in integrative medicine for food sensitivity management.
Quercetin is a widely distributed dietary flavonoid with evidence from in vitro and animal studies showing GLP-1-stimulating activity. Reviews of natural GLP-1 modulators consistently include quercetin among compounds with potent effects on GLP-1 secretion from intestinal L-cells.
Quercetin competitively inhibits xanthine oxidase (XO), the enzyme responsible for uric acid production, via the same pathway targeted by allopurinol. A randomized, double-blinded, placebo-controlled crossover trial (Br J Nutr 2016) found 500 mg/day for 4 weeks significantly lowered plasma uric acid in pre-hyperuricemic males. Real-world clinical studies using Quercetin Phytosome also demonstrated meaningful serum uric acid reductions in adults with elevated levels.
Quercetin has been identified as one of the natural products with the highest antioxidant, anti-inflammatory, and antimicrobial activity for periodontal disease in a comprehensive review. It improves oxidative stress of periodontal ligament cells, prevents alveolar bone resorption, and dampens production of IL-1β, IL-6, IL-8, and TNF-α. Preclinical evidence supports its role against crestal bone loss in periodontitis.
Quercetin is a flavonol polyphenol that modulates gut microbiota composition through probiotic-like promotion of beneficial bacterial species, inhibition of pathogenic bacteria, and enhancement of gut barrier tight junctions. Multiple preclinical and emerging clinical studies confirm bidirectional gut microbiota–quercetin interactions.
Quercetin is one of the most abundant dietary flavonoids and has demonstrated senolytic and anti-inflammatory properties relevant to healthy aging. It inhibits NF-κB, activates AMPK and Nrf2, and in combination with dasatinib has been shown in human pilot trials to reduce senescent cell burden and inflammaging markers in older adults.
Quercetin is a flavonoid antioxidant identified as relevant to aging eye health for its ability to inhibit glycation, reduce oxidative stress in lens epithelial cells, and protect retinal cells from oxidative damage. It is cited in ocular health literature as an anti-glycation and antioxidant agent for cataract prevention, and its anti-angiogenic and neuroprotective properties are relevant to AMD.
Quercetin is a flavonoid antioxidant with demonstrated protective effects against cisplatin-induced and noise-induced cochlear damage in animal models. It inhibits NF-κB inflammatory signaling in cochlear hair cells and is included in evidence-referenced hearing health formulations. Quercetin also has vasodilatory effects that may support cochlear blood flow.
Quercetin, a widely distributed dietary flavonoid, has clinical and meta-analytic evidence supporting modest cardiovascular benefits, particularly reductions in blood pressure and oxidized LDL. Multiple randomized controlled trials and meta-analyses confirm statistically significant, though modest, antihypertensive effects, especially at doses above 500 mg/day. Evidence for lipid lowering is more mixed, and most mechanistic data still derive from preclinical studies.
Quercetin is a flavonol included in evidence-based multi-flavonoid combinations for hemorrhoidal disease. A 2018 double-blind multicenter RCT (n=154) using a flavonoid mixture including quercetin showed safe and effective reduction in hemorrhoidal bleeding. A 2021 PMC retrospective study incorporating quercetin 140 mg/day achieved 89.8% hemorrhoid grade reduction in grade II–III disease.
Quercetin significantly reduced HSV-1 infectivity at 62–125 µM concentrations in Vero cells, comparably to acyclovir, in a 2024 in vitro study. A 2025 study confirmed quercetin inhibits HSV-1 replication in corneal epithelial cells and suppresses keratitis progression. Quercetin activates AMPK, suppresses NF-κB, and targets multiple viral replication stages.
Quercetin is a flavonoid that inhibits mast cell degranulation and histamine release, making it relevant for histamine intolerance management. In vitro studies show quercetin equals or exceeds cromolyn sodium in blocking histamine secretion from human mast cells. It also inhibits histamine-induced calcium influx via H4 receptors and reduces pro-inflammatory cytokines IL-6, IL-8, and TNF-α.
Quercetin is a flavonol with extensive preclinical evidence for IBD, inhibiting NF-κB, reducing pro-inflammatory cytokines, protecting intestinal epithelial barrier integrity, and modulating gut microbiota. Clinical evidence is emerging but primarily based on preclinical and in vitro data with some human study support.
Quercetin, a flavonoid found in onions, apples, and berries, improves insulin sensitivity in rodent models and shows AMPK activation. Human evidence includes a 17.5% improvement in HOMA-IR in women with PCOS (n=82) after 12 weeks at 1000 mg/day. It is a known AMPK activator alongside berberine, naringenin, and resveratrol.
Quercetin has the strongest direct clinical evidence among natural supplements for IC. An open-label trial (Katske et al., Tech Urol 2001) in 22 IC patients using 500 mg twice daily for 4 weeks showed 19/20 completers had significant improvement in IC symptom and problem indices and global pain scores. It is also the primary anti-inflammatory component of the multi-agent CystoProtek supplement tested in a 252-patient uncontrolled trial.
Quercetin is identified in the 2018 PubMed systematic review of dietary plants for kidney stone prevention as an 'antioxidant dietary phyto-phenol effective for the prevention of urolithiasis.' It is a principal active constituent of multiple kidney-supportive herbs including nettle, goldenrod, and green tea, and exerts direct renoprotective effects via antioxidant and anti-inflammatory mechanisms across multiple animal kidney injury models.
Quercetin is a ubiquitous flavonoid with well-documented antioxidant and anti-inflammatory properties that extend to nephroprotection. Multiple preclinical studies demonstrate its ability to reduce nephrotoxin-induced kidney damage, protect against diabetic nephropathy, and reduce renal fibrosis markers. Clinical studies in CKD and dialysis patients have shown reductions in inflammatory biomarkers and oxidative stress markers with quercetin supplementation.
Quercetin is a flavonoid identified as directly inhibiting glycolate oxidase—a key enzyme in endogenous oxalate synthesis—thereby reducing urinary oxalate. A PMC systematic review identified quercetin as one of the phytochemicals effective for prevention of urolithiasis. It is found in multiple antiurolithic plants including Tribulus terrestris and has been studied in preclinical models for calcium oxalate stone prevention.
Quercetin, a dietary flavonoid, has demonstrated ability to enhance intestinal barrier function by promoting assembly of tight junction proteins ZO-2, occludin, and claudin-1. In vitro studies in Caco-2 cell monolayers confirmed increased transepithelial electrical resistance and reduced paracellular permeability. It also stabilizes mast cells, reducing histamine-driven barrier disruption. A 2023 review in MDPI Molecules identified quercetin among the polyphenols most studied for leaky gut.
Quercetin modulates hepatic detoxification pathways by activating the Nrf2 transcription factor and upregulating phase I, II, and III xenobiotic-metabolizing enzymes. In animal studies, oral quercetin after CCl4 intoxication significantly reduced ALT/AST liver injury markers and restored antioxidant enzyme expression. Quercetin and its metabolite isorhamnetin have been shown in human cell line studies to reduce benzo[a]pyrene-induced cytotoxicity and BPDE-DNA adduct formation by modulating AhR and NRF2 pathways.
Quercetin is a plant flavonoid with potent antioxidant and anti-inflammatory properties investigated in COPD. A pilot Phase II RCT (14 COPD patients, 2000 mg/day, 6 months) found quercetin significantly reduced BAL IL-8, IL-1β, 8-isoprostane, and serum surfactant protein D compared to placebo. Epidemiological data links quercetin-rich diets to lower asthma incidence and reduced COPD severity.
Quercetin demonstrated bacteriostatic and bactericidal anti-spirochetal effects against B. burgdorferi in in vitro PMC studies. It inhibits NF-κB and pro-inflammatory cytokines relevant to Lyme disease-related inflammation and arthritis. Its biofilm-disrupting properties and ability to potentiate antibiotic effects have been documented. Present in many Lyme-relevant botanicals including Japanese knotweed and Baikal skullcap.
Quercetin is a gamma-benzopyrone flavonoid classified as a venoactive compound in pharmacological reviews of lymphedema treatment, reducing vascular leakage and capillary filtration rates relevant to lymphedema. It is also cited as a synergistic ingredient enhancing effects of serrapeptase and nattokinase in lymphedema enzyme protocols. Its mechanism involves inhibition of hyaluronidase, capillary hyperpermeability reduction, and anti-inflammatory NF-κB pathway modulation.
Quercetin is a flavonol with antioxidant, anti-inflammatory, and anti-angiogenic properties relevant to AMD. It was evaluated in a Phase 2 RCT (n=32, 24 months) as part of the RQC combination (resveratrol, quercetin, curcumin) in intermediate AMD, which showed significant reduction in drusen volume versus controls. Quercetin inhibits VEGF, NF-κB, and oxidative stress pathways in RPE cells in preclinical studies.
Quercetin is one of the most extensively studied natural mast cell stabilizers. In vitro studies in human mast cells show it inhibits histamine release, suppresses tryptase activity, and blocks IgE-dependent degranulation via Ca2+ influx inhibition and NF-κB suppression. It has outperformed the pharmaceutical mast cell stabilizer cromolyn in some cell-based human mast cell assays. Typical supplemental doses studied range from 500–1,000 mg/day.
Human clinical trial evidence for quercetin's direct effect on memory is mixed and largely negative. A large RCT (n=941, 500 or 1000 mg/day for 12 weeks) found no significant effects on memory, psychomotor speed, reaction time, attention, or cognitive flexibility despite large increases in plasma quercetin. A small RCT using a quercetin-enriched herbal combination (1500 mg/day for 8 weeks) showed improved working memory in menopausal women, but the multi-herb formula prevents attribution to quercetin alone.
Multiple randomized controlled trials and meta-analyses have examined quercetin's effects on the core components of metabolic syndrome (MetS) — elevated blood glucose, dyslipidemia, hypertension, and systemic inflammation. A 2024 dose-response meta-analysis of 20 RCTs found significant reductions in fasting blood glucose and systolic blood pressure. A separate meta-analysis of 16 RCTs showed significant decreases in total cholesterol, LDL-cholesterol, and CRP. Clinical evidence is real but still limited in scale and effect size, and some MetS components such as triglycerides, HDL, and waist circumference showed no significant change.
Quercetin, a polyphenolic flavonoid found widely in fruits and vegetables, has documented effects on multiple components of metabolism, including glucose regulation, lipid homeostasis, and insulin sensitivity. Clinical meta-analyses of randomized controlled trials show significant, if modest, reductions in fasting blood glucose, LDL-cholesterol, total cholesterol, and systolic blood pressure. The primary mechanistic driver appears to be activation of the AMPK signaling pathway, which simultaneously suppresses fatty acid synthesis and promotes fatty acid oxidation. Human clinical evidence exists but remains limited in scale and follow-up duration, so findings should be interpreted cautiously.
Quercetin activates the AMPK/PGC-1α pathway to stimulate mitochondrial biogenesis and has been studied together with resveratrol for synergistic effects on mitochondrial energy capacity. It also modulates EGCG-like pathways promoting Nrf2 antioxidant defenses that protect mitochondrial function.
Quercetin, a widely distributed plant flavonoid, has been studied for reducing mycotoxin-induced cytotoxicity in multiple cell systems. A 2020 PMC review of quercetin's pharmacology specifically stated it plays an important role in reducing mycotoxins and protecting cells from damage. It exerts antioxidant and anti-inflammatory activities against mycotoxin-mediated oxidative stress via ROS scavenging and NRF2 activation, though data from Caco-2 studies suggest caution at high doses with ochratoxin A.
Quercetin supplementation (1000 mg/day) has been shown in a systematic review and meta-analysis of 13 RCTs (249 participants) to significantly reduce muscle soreness at 0–24 h post-exercise (SMD: -1.33), creatine kinase at 24–48 h (SMD: -1.15), and post-exercise oxidative stress (SMD: -0.92).
Quercetin is one of the primary active flavonoids identified in Chinese herbal medicine formulae for MG in a 2022 Frontiers in Microbiology clinical study of a modified Buzhong Yiqi formula that significantly improved symptoms in 30 MG patients. The 2018 CHM systematic review also noted that flavonoids from Buzhong Yiqi Decoction exhibited anti-acetylcholinesterase effects.
Quercetin is a plant flavonoid that augments nitric oxide status in humans by raising plasma S-nitrosothiols, plasma nitrite, and urinary nitrate while reducing endothelin-1 in a randomized crossover RCT. It is well characterized as a dietary polyphenol that activates eNOS and enhances endothelial NO production.
Quercetin is a flavonoid with preclinical evidence demonstrating inhibition of osteoclast differentiation and promotion of osteoblast activity via multiple signaling pathways. The Frontiers in Nutrition (2024) osteoporosis nutraceuticals review identified quercetin among bone-protective phytochemicals. Animal studies consistently show quercetin prevents ovariectomy-induced bone loss.
Quercetin is a flavonoid with anti-inflammatory properties shown to benefit bladder pain and interstitial cystitis (IC), conditions that overlap with OAB. A clinical trial (Katske et al., Tech Urol 2001) found quercetin supplementation improved IC symptoms at 4 weeks. Naturopathic guidelines reference quercetin for bladder inflammation underlying OAB. However, no placebo-controlled RCT has tested quercetin as a standalone treatment specifically for OAB.
Quercetin, a natural flavonoid, demonstrates antioxidant, anti-inflammatory, and immunomodulatory properties relevant to acute pancreatitis (AP) in multiple preclinical studies. In cerulein-induced AP mouse models, quercetin pretreatment reduced pancreatic edema, inflammatory cell infiltration, acinar necrosis, TNF-α expression, and myeloperoxidase activity. A 2025 comprehensive review in Frontiers in Pharmacology highlights its multifaceted therapeutic potential for AP, though clinical validation is still needed.
Quercetin is a polyphenol flavonoid with anti-androgenic, anti-inflammatory, and insulin-sensitizing properties studied in PCOS. Preclinical studies show it reduces testosterone, restores ovarian function, and upregulates CYP19a1 (aromatase). Clinical evidence is emerging from RCTs showing improvements in androgen and metabolic parameters.
Quercetin has been directly studied in a carrageenan-induced pleural inflammation rat model, demonstrating significant antioxidant and anti-inflammatory effects in blood and lung tissue at both 4 and 24 hours post-carrageenan injection. It inhibits phospholipase A2 and enzymes of lipid peroxidation, reducing leukotriene synthesis relevant to pleural inflammation. A second study confirmed quercetin and resveratrol together reduce inflammatory markers in pleurisy exudates.
Quercetin is a flavonoid with antiviral, anti-inflammatory, and immunomodulatory properties investigated for COVID-19 pneumonia. It is a key bioactive antiviral component in propolis active against SARS-CoV-2 and respiratory pathogens. Preclinical studies show it reduces lung inflammation in bacterial and viral pneumonia models via NF-κB and NLRP3 inhibition.
In a 2006 pilot study of 5 FAP patients, the combination of curcumin (480 mg) and quercetin (20 mg) three times daily for 6 months reduced polyp number by 60.4% and polyp size by 50.9% (both p<0.05). Animal studies show quercetin reduces adenoma load in ApcMin/+ mice via IL-6/STAT3 pathway suppression. Quercetin is characterized as a chemopreventive candidate for colorectal polyps in multiple peer-reviewed reviews.
A widely studied flavonoid with anti-inflammatory, antiviral, and immunomodulatory properties, Quercetin has been included in peer-reviewed post-COVID-19 recovery protocols. Clinical evidence documents its ability to reduce inflammatory cytokines and support immune reconstitution after viral illness.
Quercetin, a flavonoid found in many plants, inhibits mast cell degranulation and histamine release, directly reducing allergic rhinitis symptoms including rhinorrhea and post-nasal drip. A 2022 randomized, double-blind, placebo-controlled trial showed quercetin-containing supplements significantly improved nasal discharge scores and allergy quality-of-life measures versus placebo. A 2025 systematic review (PRISMA, 18 studies) confirmed preclinical and emerging clinical evidence for its role in allergic rhinitis.
Quercetin is a flavonoid with anti-inflammatory and antioxidant properties studied for reducing post-surgical inflammation and oxidative stress. It inhibits NF-κB and pro-inflammatory cytokine production, supporting tissue recovery. Reviews of nutritional strategies for injury and surgical recovery include quercetin as a relevant polyphenol.
Quercetin has been studied in several clinical trials for COVID-19 and early long COVID symptoms, with doses of 500–1500 mg/day associated with faster recovery, reduced inflammation, and improved viral clearance. It has demonstrated antiviral properties against multiple respiratory viruses by inhibiting viral proteases, polymerases, and reverse transcriptase. A 2020 PMC review proposed quercetin and vitamin C as a synergistic post-viral therapy.
Quercetin, a flavonol abundant in onions, apples, and capers, has demonstrated anti-prostate cancer activity in multiple in vitro and in vivo studies, including inhibition of prostate cancer cell growth and enhancement of green tea catechin bioavailability in prostate tissue. A prospective RCT (n=31) confirmed quercetin penetrates prostate tissue. Preclinical studies also show activity against BPH.
A randomized double-blind placebo-controlled trial found quercetin (500 mg twice daily) significantly reduced IPSS in men with CP/CPPS, with 67% achieving >25% improvement versus 20% placebo. Clinical studies have demonstrated efficacy of quercetin on BPH-associated LUTS. Quercetin is a recommended treatment in the UPOINT prostatitis classification system and inhibits androgen receptor signaling and NF-κB–mediated prostate inflammation.
Quercetin is a flavonol studied for psoriasis due to its inhibition of NF-κB, TNF-α, IL-6, and IL-17, and suppression of keratinocyte hyperproliferation. Preclinical studies demonstrate significant reduction in psoriasis-like symptoms in animal models; limited small clinical studies report benefits. It is identified in multiple PMC reviews as a promising anti-psoriatic compound.
Quercetin inhibits IgE-mediated mast cell degranulation and histamine release, making it relevant to urticaria. A 2025 Phytotherapy Research study showed it alleviates chronic urticaria via the CD300f/SHP-1 signaling pathway. A 2025 PRISMA meta-analysis (13 murine studies, Frontiers in Pharmacology) confirmed significant reductions in IgE, histamine, IL-4, and TNF-α. Small-scale human observational data are supportive but large RCTs are still needed.
Quercetin is a flavonoid that suppresses RA-relevant inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8), inhibits NF-κB and fibroblast-like synoviocyte invasion, and reduces osteoclastogenesis. A 2025 network meta-analysis of 18 RA RCTs ranked quercetin as the most effective plant substance for reducing VAS pain scores (SUCRA 67.3%).
A 2025 PubMed-indexed RCT (PMID 40177799, n=82) evaluated topical compound heparin sodium allantoin gel containing quercetin (as the primary active from onion extract) in papulopustular rosacea, showing improvements in erythema scores and skin barrier function (TEWL, hydration) at 12 weeks. Quercetin also inhibits mast cell degranulation and NF-κB relevant to rosacea flushing.
Quercetin is the primary bioactive flavonoid in onion extract and has been directly studied for anti-scarring effects. It suppresses TGF-β and IGF-1 signaling, inhibits keloid fibroblast proliferation, reduces ECM deposition, and induces MMP-1 to promote ECM remodeling in scar tissue.
Quercetin is a flavonoid that stabilizes mast cells and inhibits histamine, leukotriene, and pro-inflammatory cytokine release. A 2022 placebo-controlled RCT in adults with hay fever showed symptom improvements at 200 mg/day for 4 weeks. NCCIH acknowledges quercetin among studied approaches for allergic rhinitis.
Quercetin is a flavonoid that stabilizes mast cells and inhibits histamine release, with preclinical and early clinical evidence for seasonal allergic rhinitis. A 2022 randomized, double-blind trial found significant symptom reduction, and a 2025 PRISMA-compliant systematic review of 18 studies confirmed consistent anti-allergic effects. Human studies show superior symptom improvement when added to standard therapy.
Quercetin inhibits mast cell degranulation, reduces histamine and pro-inflammatory cytokine production, and has demonstrated efficacy in murine allergic rhinitis models for reducing nasal congestion, sneezing, and rhinorrhea. Two clinical trials reported symptom reduction in allergic disease; it is regarded as a supportive treatment for allergy-related nasal congestion. Mechanistic evidence is robust though large-scale human RCTs are still limited.
Quercetin inhibits mast cell degranulation and NF-κB signaling, reducing histamine release and pro-inflammatory cytokines relevant to sinusitis. A 2024 narrative review in SAGE Open Medicine identified quercetin among supplements with growing positive evidence for sinusitis. It is often combined with bromelain for sinus-related inflammation.
Quercetin has been investigated for anti-aging effects in human skin tissue (ex vivo) and in at least one clinical topical study. It suppresses UV-induced MMP-1 (a key enzyme in wrinkle formation) and COX-2 in human skin tissue, inhibiting AP-1 and NF-κB pathways. A clinical study using oak quercetin in an SPF 15 cream demonstrated measurable improvements in wrinkling, elasticity, smoothness, radiance, and moisture. A 2024 systematic review and meta-analysis confirmed significant antioxidant effects relevant to skin aging across 65 studies.
Quercetin is a flavonol with anti-inflammatory, antioxidant, and capillary-stabilizing properties increasingly studied for chronic venous disease including spider veins. It inhibits key pro-inflammatory cytokines (TNF-α, IL-6) and is found in citrus-based venoactive formulas. Authoritative reviews identify quercetin as relevant to venous pathology management.
Quercetin is a flavonol polyphenol with documented photoprotective effects against UV-induced skin inflammation, oxidative stress, and immunosuppression. It is included in multiple phytochemical photoprotection reviews as having chemopreventive effects against photocarcinogenesis through inhibition of UV-activated cellular signaling pathways.
Quercetin, a common dietary flavonoid, has demonstrated preventive and therapeutic effects on dental hard tissue erosion and demineralization in a systematic review and meta-analysis. It significantly reduced dentin erosion loss in both preventive and therapeutic protocols, potentially through pellicle layer modification and collagen crosslinking.
Quercetin, a widely distributed flavonol, has been shown in multiple meta-analyses to significantly reduce serum triglycerides and total cholesterol. It inhibits fatty acid synthesis, activates PPAR-alpha, and reduces oxidative stress. Meta-analyses confirm TG-lowering in cardiometabolic disease populations.
Quercetin has antiviral activity against influenza, RSV, and rhinoviruses in preclinical studies, and a double-blind RCT in athletes (n=40) found significant reduction in URTI episodes (1 vs. 9 in placebo). It inhibits viral neuraminidase, NF-κB signaling, and enhances interferon responses relevant to upper respiratory defense.
Quercetin is a flavonoid with anti-inflammatory, anti-biofilm, and antimicrobial activities relevant to urinary tract health. It is used clinically for chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), where a randomized double-blind trial showed significant symptom score improvement. It is also studied in combination with other compounds for recurrent UTI prevention.
Quercetin has preclinical evidence for anti-uterine fibroid activity, demonstrating inhibition of extracellular matrix expression in primary human uterine leiomyoma cells in a 2020 study. It also has anti-inflammatory and anti-proliferative properties relevant to endometrial health.
Quercetin is a flavonoid polyphenol with well-documented broad-spectrum antiviral activity. It inhibits viral entry and replication across multiple virus families including SARS-CoV-2, influenza, HSV, RSV, HCV, and Ebola. A pragmatic RCT in early-stage COVID-19 confirmed clinical benefit when combined with curcumin alongside standard of care.
Quercetin is a flavonoid with antioxidant and cytoprotective effects on melanocytes demonstrated in vitro. Combined with green tea extract and folic acid it shows synergistic protection against H2O2-induced melanocyte cell death in cell culture, directly modeling vitiligo conditions. Practical Dermatology (2025) lists quercetin among alternative therapeutics with evidence relevant to vitiligo management.
Quercetin, a ubiquitous flavonoid, promotes wound healing through anti-inflammatory, antioxidant, and collagen-stabilizing mechanisms. Multiple in vitro and animal studies demonstrate it accelerates wound closure, enhances fibroblast proliferation, and inhibits matrix metalloproteinases involved in pathological wound remodeling.
Quercetin is a flavonoid found in onions, capers, and many plant foods. It inhibits 5-alpha reductase and androgen receptor signaling in cell models, reduces DHT-induced follicle apoptosis, and has anti-inflammatory properties relevant to alopecia areata (quercetin is proposed as the active agent in onion juice's clinical effect). In vivo mouse studies show quercetin promotes hair growth.
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