Health Care Professional Information
Scientific Name
3,3',4',5,7-pentapentahydroxyflavone
Clinical Summary
Quercetin is a flavonol that constitutes the major bioflavonoid sources in the human diet. The glycoside form is readily available in dietary plants such as teas, onions, apple and buckwheat (5). Quercetin is thought to have antioxidant, anti-inflammatory and anti-allergic properties. In vitro data suggest quercetin may have anti-cancer effects (1), but more research is needed to explore this potential.
Quercetin was shown to exacerbate estrogen-induced breast tumors in rats (12).
Food Sources
Teas, onions, apples, buckwheat
Mechanism of Action
Quercetin constitutes the major bioflavonoid in the human diet. Its antioxidant activity is due to the reactivity of its phenolic group, which reacts with free radicals to form the more stable phenoxy radicals (1). Quercetin is thought to have anti-inflammatory and anti-allergy properties. The proposed mechanism of action is inhibition of lipoxygenase and cyclooxygenase resulting in reduced production of inflammatory mediators (e.g., leukotrienes and histamine). Quercetin appears to inhibit cyclooxygenase to a greater degree than lipoxygenase. It also has been shown to have membrane-stabilizing capabilities and to inhibit aldose reductase and low-density lipoprotein oxidation (8). Significant antiviral activity has been shown in vitro and in vivo. Proposed anti-cancer mechanisms of action include down-regulation of mutant p53 proteins; G1 phase arrest (1); tyrosine kinase inhibition (10); estrogen receptor binding; inhibition of heat shock proteins; and RAS protein expression inhibition (1). Presently, considerable in vitro data support the concept of quercetin as an anti-cancer compound. However, clinical studies that support these uses are few and the results are mixed (7) (9).
Pharmacokinetics
Absorption
Following oral administration, quercetin glycosides are absorbed from the gut. These glycosides may then undergo hydrolysis in the enterocyte via b-glucosidases before draining into the portal vein. Absorption rate from dietary sources is influenced by the position and chemical nature of the glycoside in combination with the various compounds in the food matrix (1).
Distribution
Quercetin is found predominantly in plasma in the form of its conjugates (e.g., quercetin glucuronides and/or sulfates) and small amounts of unconjugated quercetin aglycone. Maximum plasma concentrations are achieved within the first two hours of administration. This suggests that the absorption site is in the upper gut compartment, and may rule out intestinal bacteria degradation (2) (3).
Excretion
Previous pharmacokinetic studies using intravenous administration suggest that quercetin is quickly eliminated in humans, with an approximate elimination half-life of less than two hours. Several studies report that quercetin is present in urine as conjugates of glucuronic acid and sulfate groups (2).
Adverse Reactions
No adverse effects have been reported with single oral doses up to 4 grams.
Herb-Drug Interactions
Papain and Bromelain: May assist the absorption of Quercetin in the intestine (6).
Quinolone antibiotic: Quercetin may compete for DNA gyrase binding sites on bacteria (5).
CYP 3A4: Quercetin was shown to significantly inhibit the constitutive CYP3A4 activity (11).
Literature Summary and Critique
Dosage (Inside MSKCC Only)
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References
- Lamson DW, Brignall MS. Antioxidant and cancer III: quercetin. Altern Med Rev 2000;5:196-208.
- Graefe EU, et al. Pharmacokinetics and bioavailability of the flavonol quercetin in humans. Int J Clin Pharmacol Therapy 1999;37:219-33.
- Erlund I, et al. Pharmacokinetics of quercetin aglycone and rutin in healthy volunteers. Eur J Clin Pharmacol 2000;56:545-53.
- Sampson S, et al. Flavonol and flavone intakes in US health professionals. J Am Diet Assoc 2002;102:1414-20.
- Herr, SM. Herb-Drug Interaction Handbook. Chuch Street books. 2nd ed. Nassau NY 2002.
- Shoskes D, et al. Quercetin in men with category III chronic prostatitis: a preliminary prospective, double-blind, placebo-controlled trial. Urology 1999;54:960-3.
- Janssen K, et al. Effects of the flavonoids quercetin and apigenin on hemostasis in healthy volunteers: results from an in vitro and dietary supplement study. Am J Clin Nutr 1998;67:255-62.
- Chopra M, et al. Nonalcoholic red wine extract and quercetin inhibit LDL oxidation without affecting plasma antioxidant vitamin and carotenoid concentrations. Clin Chem 2000;46:1162-70.
- Beatty ER, et al. Effect of dietary quercetin on oxidative DNA damage in healthy human subjects. Br J Nutr 2000;84:919-25.
- Ferry DR, et al. Phase I clinical trial of the flavonoid quercetin: pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Clin Cancer Res 1996;2:659-68.
- Sergent T, Dupont I, Van der Heiden E, et al. CYP1A1 and CYP3A4 modulation by dietary flavonoids in human intestinal Caco-2 cells. Toxicol Lett. 2009 Dec 15;191(2-3):216-22.
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Consumer Information
How It Works
Bottom Line: Quercetin may be helpful in relieving the symptoms of prostatitis, but there is no proof that it can treat cancer, heart disease, asthma, colitis, or any other medical condition.
Quercetin belongs to a family of compounds called bioflavonoids, which are largely responsible for the bright colors and medicinal activities of many plants. Quercetin is the most common bioflavonoid that people consume, and is the most active of the bioflavonoids in laboratory experiments. It is known to act as an antioxidant, neutralizing free radicals that can cause cellular and DNA damage. Quercetin is thought to have anti-inflammatory and anti-allergy properties by inhibiting the release of substances that mediate the inflammatory response, such as histamine. A study in healthy volunteers suggests that quercetin inhibits low-density lipoprotein (LDL) oxidation, which may be involved in the development of atherosclerosis and cancer. Significant antiviral activity has been shown in laboratory and animal experiments. Presently, considerable laboratory data support the concept of quercetin as an anticancer compound, but it is still unclear from clinical trials whether this effect occurs in the human body.
Purported Uses
- To treat allergies
Extensive laboratory studies show an anti-inflammatory effect of quercetin, including inhibition of histamine release, but there is no proof from clinical trials that this effect occurs in humans.
- To prevent and treat cancer
Extensive laboratory studies show anti-cancer activity of quercetin against a wide range of cancer cell types, but there is no proof from clinical trials that it can prevent or treat cancer.
- To treat heart disease
One study showed that quercetin, in combination with red wine extract, lowered LDL oxidation (which may contribute to atherosclerosis) in healthy volunteers. However, it is unclear how much of this effect was due to quercetin alone, and other similar studies have not found the same effect. There is no other proof that quercetin can treat heart disease.
- To reduce inflammation (in conditions such as asthma, inflammatory bowel disease, psoriasis, and colitis)
Extensive laboratory studies show an anti-inflammatory effect of quercetin, but there is no proof from clinical trials that quercetin can treat these conditions.
Research Evidence
Chronic prostatitis (chronic pelvic pain syndrome)
Thirty men with category III chronic prostatitis (chronic pelvic pain syndrome) took part in a study of the effects of quercetin. They were randomly assigned to take either 500 mg of quercetin or a placebo pill by mouth twice a day for one month. More men taking quercetin reported significant improvements in quality of life and symptoms (67%) as compared to men taking the placebo pill (20%). This study also suggested that bromelain and papain can enhance the absorption of quercetin. Because the sample size of this clinical trial is relatively small, larger studies are needed to substantiate these results.
Prevention of DNA damage
The effect of dietary quercetin on DNA damage was measured in a study with 36 healthy volunteers. Fifty percent of the volunteers were given a low-quercetin diet for 14 days, followed by a seven-day “washout” period of normal diet, and 14 days of high-quercetin diet (one onion cake and one glass of black tea daily). The other volunteers were given the high-quercetin diet first and the low-quercetin diet second. DNA damage in white blood cells was measured before and after each diet period. Volunteers were found to have the same levels of DNA damage after eating both the high- and low-quercetin diets, indicating that quercetin has no short-term effects on DNA damage in white blood cells. This study is small and does not examine the long-term effects of a high-quercetin diet.
Do Not Take If
- You are taking quinolone antibiotics (Quercetin may lessen their effect).
Side Effects
- No side effects have been reported with single oral doses of up to 4 grams.
Special Point
- The fruit extracts papain and bromelain may help increase the absorption of Quercetin in the intestine.
- Quercetin was shown to exacerbate estrogen-induced breast tumors in rats.
Last updated: September 28, 2012
absorption (ub-SORP-shun)
The process of taking nutrients from the digestive system into the blood so they can be used in the body.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)acid (A-sid)
A chemical that gives off hydrogen ions in water and forms salts by combining with certain metals. Acids have a sour taste and turn certain dyes red. Some acids made by the body, such as gastric acid, can help organs work the way they should. An example of an acid is hydrochloric acid. Acidity is measured on a scale called the pH scale. On this scale, a value of 7 is neutral, and a pH value of less than 7 to 0 shows increasing acidity.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)administration (ad-MIH-nih-STRAY-shun)
In medicine, the act of giving a treatment, such as a drug, to a patient. It can also refer to the way it is given, the dose, or how often it is given.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)anti-inflammatory (AN-tee-in-FLA-muh-TOR-ee)
Having to do with reducing inflammation.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)antioxidant (AN-tee-OK-sih-dent)
A substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism). Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)antiviral (AN-tee-VY-rul)
A drug used to treat infections caused by viruses.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)bacteria (bak-TEER-ee-uh)
A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The singular of bacteria is bacterium.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)blood (blud)
A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)breast (brest)
Glandular organ located on the chest. The breast is made up of connective tissue, fat, and breast tissue that contains the glands that can make milk. Also called mammary gland.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)bromelain (BROH-meh-layn)
An enzyme found in pineapples that breaks down other proteins, such as collagen and muscle fiber, and has anti-inflammatory properties. It is used as a meat tenderizer in the food industry.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)cancer (KAN-ser)
A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord. Also called malignancy.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)cardiovascular (KAR-dee-oh-VAS-kyoo-ler)
Having to do with the heart and blood vessels.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)cell (sel)
The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)chemical (KEH-mih-kul)
A substance made up of elements, such as hydrogen or sodium.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)chronic (KRAH-nik)
A disease or condition that persists or progresses over a long period of time.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)clinical (KLIH-nih-kul)
Having to do with the examination and treatment of patients.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)clinical trial (KLIH-nih-kul TRY-ul)
A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called clinical study.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)compound (KOM-pownd)
In science, a substance that is made up of more than one ingredient.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)diet (DY-et)
The things a person eats and drinks.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)DNA
The molecules inside cells that carry genetic information and pass it from one generation to the next. Also called deoxyribonucleic acid.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)estrogen (ES-truh-jin)
A type of hormone made by the body that helps develop and maintain female sex characteristics and the growth of long bones. Estrogens can also be made in the laboratory. They may be used as a type of birth control and to treat symptoms of menopause, menstrual disorders, osteoporosis, and other conditions.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)extract (EK-strakt)
In medicine, a preparation of a substance obtained from plants, animals, or bacteria and used as a drug or in drugs.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)follow-up (FAH-loh-up)
Monitoring a person's health over time after treatment. This includes keeping track of the health of people who participate in a clinical study or clinical trial for a period of time, both during the study and after the study ends.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)histamine (HIS-tuh-meen)
A substance that has many effects in the body. It is released from some types of white blood cells during allergic reactions. It causes small blood vessels to dilate (widen) and become leaky, which can cause tissues to swell. It also causes smooth muscles to contract, gastric acid to be made, and the heart rate to increase. Histamine is used in tests for allergies, asthma, and gastric acid secretion. It is a type of neurotransmitter.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)hydrolysis (hy-DRAH-lih-sis)
A chemical reaction that uses water to break down a compound.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)in vitro (in VEE-troh)
In the laboratory (outside the body). The opposite of in vivo (in the body).
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)in vivo (in VEE-voh)
In the body. The opposite of in vitro (outside the body or in the laboratory).
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)inflammatory (in-FLA-muh-TOR-ee)
Having to do with inflammation (redness, swelling, pain, and a feeling of heat that helps protect tissues affected by injury or disease).
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)intestinal (in-TES-tih-nul)
Having to do with the intestines.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)intestine (in-TES-tin)
The long, tube-shaped organ in the abdomen that completes the process of digestion. The intestine has two parts, the small intestine and the large intestine. Also called bowel.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)intravenous (IN-truh-VEE-nus)
Into or within a vein. Intravenous usually refers to a way of giving a drug or other substance through a needle or tube inserted into a vein. Also called IV.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)kinase (KY-nays)
A type of enzyme that causes other molecules in the cell to become active. Some kinases work by adding chemicals called phosphates to other molecules, such as sugars or proteins. Kinases are a part of many cell processes. Some cancer treatments target certain kinases that are linked to cancer.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)oral (OR-ul)
By or having to do with the mouth.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)oxidation (OK-sih-DAY-shun)
A chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance. Examples of oxidation are rust and the brown color on a cut apple.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)pelvic (PEL-vik)
Having to do with the pelvis (the lower part of the abdomen located between the hip bones).
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)placebo (pluh-SEE-boh)
An inactive substance or treatment that looks the same as, and is given the same way as, an active drug or treatment being tested. The effects of the active drug or treatment are compared to the effects of the placebo.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)plasma (PLAZ-muh)
The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clots are in plasma.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)portal vein (POR-tul vayn)
A blood vessel that carries blood to the liver from the stomach, small and large intestines, spleen, pancreas, and gallbladder. Also called hepatic portal vein.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)prostatitis (PROS-tuh-TY-tis)
Inflammation of the prostate gland.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)protein (PROH-teen)
A molecule made up of amino acids that are needed for the body to function properly. Proteins are the basis of body structures such as skin and hair and of substances such as enzymes, cytokines, and antibodies.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)quality of life (KWAH-lih-tee ... life)
The overall enjoyment of life. Many clinical trials assess the effects of cancer and its treatment on the quality of life. These studies measure aspects of an individual’s sense of well-being and ability to carry out various activities.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)randomized
Describes an experiment or clinical trial in which animal or human subjects are assigned by chance to separate groups that compare different treatments.
(http://www.cancer.gov/dictionary)receptor (reh-SEP-ter)
A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific physiologic effect in the cell.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)response (reh-SPONTS)
In medicine, an improvement related to treatment.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)significant (sig-NIH-fih-kunt)
In statistics, describes a mathematical measure of difference between groups. The difference is said to be significant if it is greater than what might be expected to happen by chance alone. Also called statistically significant.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)syndrome (SIN-drome)
A set of symptoms or conditions that occur together and suggest the presence of a certain disease or an increased chance of developing the disease.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)urine (YOOR-in)
Fluid containing water and waste products. Urine is made by the kidneys, stored in the bladder, and leaves the body through the urethra.
Source: The National Cancer Institute's Dictionary of Cancer Terms
(http://www.cancer.gov/dictionary)
