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Quercetin

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Related terms
Background
Evidencetable
Tradition
Dosing
Safety
Attribution

Related Terms
  • Allium cepa, American elder, apples, Artemisia abrotanum L, AS195 Folia vitis viniferae (red vine leaf extract), biflavonoids, bilberries, black currants, black tea, brassica vegetables (cabbage, broccoli, cauliflower, turnips, kale), buckwheat tea, citrus bioflavonoid, endive, flavones, flavonoids, flavonols, flavon(ol)-glycosides, Ginkgo biloba extract, ginkgo flavone glycosides, grapefruit, green tea, Hypericum perforatum L., isoflavones, isorhamnetin, isoquercitrin, kaemferol, meletin, Myrtaceae, naphthodianthrones, onion, parsley (Petroselinum crispum (Mill.) Nym.), phytodrug (QG-5), phytoestrogens, pine bark extract, polyphenol, Psidium guajava L. (Fam.), quercetin aglycone, quercetin chalcone, quercetin dimethyl-ethers, quercetin glucoside, quercetin glucuronides, quercetin rutin, quercetin rutinoside, red vine leaf extract, red wine, red wine phenolics, rhamnose molecule, rutin, Sambucas nigra L., sophretin, St. John's wort, STW-3, Tycho, Venenkapseln, Venoruton (O-(beta-hydroxyethyl) rutosides (HR).

Background
  • Quercetin is a major flavonol, one of the almost 4,000 flavonoids (antioxidants) that occur in foods of plant origin, such as red wine, onions, green tea, apples, berries, and Brassica vegetables (cabbage, broccoli, cauliflower, turnips). Quercetin is also found in Gingko biloba, St. John's wort, and American elder.
  • Quercetin and rutin (another flavonol) are used in many countries as vasoprotectants (protects blood vessels) and are ingredients of numerous multivitamin preparations and herbal remedies. They occur mainly as glycosides, which means they are linked with various sugars. However, the ability of the body to absorb these compounds is questionable.
  • Quercetin and other flavonols have a wide variety of biological effects, but the scientific evidence for use in the prevention or treatment of disease is weak. Quercetin has been considered as a therapy for cardiovascular diseases, high cholesterol, diabetic cataracts, inflammation, ischemic injury, chronic prostatitis, chronic venous insufficiency, gastrointestinal ulceration, hepatitis, allergies, asthma, viral infections, and hay fever.
  • Review of the literature shows that there have been several studies on the association of quercetin and with the risk reduction for coronary heart disease and stroke, high blood pressure, cancers, and a few studies on other medical conditions. However, there is a lack of strong evidence to support any of these conditions.

Evidence Table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. GRADE *


Several of the effects of flavonoids that have been observed in laboratory and animal studies suggest that they might be effective in reducing cardiovascular disease risk. Studies in humans using polyphenolic compounds from red grapes showed improvement in endothelial function in patients with coronary heart disease. Antioxidant and cholesterol-lowering effects are proposed.

C


Population-based studies report that quercetin is associated with a reduced risk of coronary heart disease and stroke. Quercetin supplementation reduced blood pressure in hypertensive rodents and hypertensive humans.
C


Quercetin does not appear to affect changes in the immune system caused by intense exercise. However, it reduced the number of respiratory tract infections in people who participated in intense cycling. More research is needed.

C


Some research suggests that quercetin may help prevent pancreatic cancer in smokers. However, quercetin did not have this effect in non-smokers or former smokers. More research is needed to determine if quercetin is beneficial.

C


There is some evidence that quercetin may be useful for the treatment of chronic prostatitis and chronic pelvic pain syndrome. Further research is needed to confirm these results.

C
* Key to grades

A: Strong scientific evidence for this use
B: Good scientific evidence for this use
C: Unclear scientific evidence for this use
D: Fair scientific evidence for this use (it may not work)
F: Strong scientific evidence against this use (it likley does not work)


Tradition / Theory

The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.

  • Allergic rhinitis, allergies, anti-aging, antihistamine, anti-inflammatory, antioxidant, antispasmodic, anti-thrombotic, arthritis, antiviral, asthma, atherosclerosis (hardening of the arteries), autoimmune diseases, brain tumors, breast cancer prevention, cancer treatment, capillary fragility, cataract prevention, cerebrovascular disease, chronic venous insufficiency, coronary heart disease, cutaneous blood flux, diabetes mellitus, diarrhea (acute), depression, DNA damage, draft healing, eczema, edema, fibromyalgia, gout, hepatitis, herpes, high cholesterol, hives, ileostomy use, inflammation, interstitial cystitis, kidney toxicity, local anesthesia, lung problems, macular degeneration, mucosal mast cell inhibition, osteoporosis, peptic ulcers, platelet aggregation, prostate cancer prevention, protection against chemotherapy side effects, retinopathy, rheumatoid arthritis, schizophrenia, systemic lupus erythematosus (SLE), ulcers, vasoprotective, viral infections, vision problems (age-related).

Dosing

Adults (over 18 years old)

  • It has been suggested that quercetin should be taken 20 minutes before meals. Quercetin has been ingested from onions, juice, black tea, and red wine. Doses of 100-500 milligrams of quercetin have been taken 2-3 times daily. It is available in tablet, capsule, or softgel form. Intravenous and intramuscular forms have been injected by a healthcare provider.

Children (under 18 years old)

  • Insufficient available evidence to recommend.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

  • Avoid in individuals with a known allergy/hypersensitivity to quercetin by ingestion or skin contact. Eye, skin, gastrointestinal and/or respiratory tract irritation is possible.

Side Effects and Warnings

  • Being a common food component, quercetin is generally safe and well tolerated at usual dietary intake. However it has been associated with headache, gastrointestinal effects, hematoma, and kidney toxicity.
  • Intravenous injection has been associated with pain at the injection site that is dose related and can be controlled by reducing the rate of infusion. Intravenous administration of quercetin has also resulted in flushing, sweating, difficulty breathing (dyspnea), nausea, mild tingling of the extremities, lethargy, and vomiting.
  • Concern had been expressed about the possible tumor-promoting effect of quercetin.
  • Mild constipation and hair thinning were reported by two of 260 patients taking AS195, which contains red vine leaf extract that is rich in quercetin.

Pregnancy and Breastfeeding

  • Insufficient available evidence.

Attribution
  • This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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