Quercetin
Also known by these names
- Polyphenolic flavonoid
- 3,3',4',5,7-pentapentahydroxyflavone
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Key Points
- Quercetin is a dietary flavonoid found in certain fruits and vegetables and some medicinal plants.
- Quercetin is used widely as an antioxidant.
- Quercetin may have anti-inflammatory and cancer prevention effects, although it’s also been shown to block apoptosis and to worsen estrogen-induced breast tumors.
- Quercetin may increase the anti-tumor effects of some chemotherapy drugs, but it may also interfere with the actions of some chemotherapy drugs.
- Quercetin may help manage some symptoms related to treatment and/or cancer.
- Quercetin may reduce side effects of some conventional cancer therapies.
- No published clinical trials to date establish quercetin as an anti-cancer therapy in humans, although preclinical studies show promising effects.
- Quercetin is of interest to BCCT because of its potential anticancer, conventional treatment enhancement and side-effect management properties.
- Quercetin is included in a number of integrative care cancer protocols.
- Although oral quercetin has low toxicity and is usually well-tolerated, it can cause side effects as well as react with some prescription drugs. Caution and medical supervision are advised.
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The flavonoid quercetin is a natural antioxidant that is found in several foods:
- Apples
- Black, green and buckwheat tea
- Onions
- Red grapes
- Cherries
- Raspberries
- Citrus fruits
Quercetin is also found in some medicinal plants such as ginkgo biloba and St. John’s Wort. It is also available as a supplement.
Treating the Cancer
Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action
Studies have found both benefits and concerns regarding effects of quercetin on cancer. Concerns are listed in the Cautions section below.
Lab and Animal Evidence
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Some effects of quercetin on cancer activity depend on the dose:
- Quercetin either increased or decreased aromatase enzyme activity in adrenocortical carcinoma cells, depending on dose.
- It inhibited prostate cancer growth in animal studies. and resensitized enzalutamide-resistant prostate cancer cells to enzalutamide treatment in mouse xenografts.
- Quercetin induced cell death (apoptosis) in cell studies and reduced tumor volume in mice bearing estrogen receptor‑positive breast cancer cells. It also suppressed tumor-promoting responses in breast cancer cells.
- It enhanced antitumor activities of doxorubicin, paclitaxel, and vincristine and reversed multidrug resistance in breast cancer cells
- Rutin, a quercetin glycoside, reversed multidrug resistance and restored chemosensitivity to cyclophosphamide and cyclophosphamide of chemoresistant, triple-negative breast cancer cells
- When used in combination with curcumin, quercetin increased sensitivity of ovarian cancer cells to cisplatin.
- It either promoted or blocked cell death (apoptosis) or promoted or reduced tumor growth in preclinical studies, depending on dose.
Some studies show benefits of quercetin, including anti-inflammatory and cancer-preventive effects. Quercetin induced cell death (apoptosis ) in cell studies and reduced tumor volume in mice bearing estrogen receptor‑positive breast cancer cells. It suppressed tumor-promoting responses in breast cancer cells.
Quercetin also seems to sensitize breast cancer cells and liver cancer cells that have become resistant to chemotherapy, making them responsive to the chemotherapy drug doxorubicin. Quercetin may also increase cancer cell sensitivity to the drugs topotecan and gemcitabine. Rutin, a quercetin glycoside, reversed multidrug resistance and restored chemosensitivity to cyclophosphamide and cyclophosphamide of human chemoresistant, triple-negative breast cancer cells
A 2017 review found that quercetin inhibited cell growth and induced cell death (apoptosis ), necrosis (the death of most or all of the cells in an organ or tissue), and autophagy (the body's consumption of its own tissue and dead cell components, another method of tumor cell elimination). Quercetin also promoted activity to fight Helicobacter pylori (H. pylori) infection in preclinical studies involving gastric cancer. H. pylori infection is associated with an increased risk of gastric cancer. In sum, quercetin promotes processes that kill cancer cells or prevent cancer cells from growing, and it counters H. pylori infection that is associated with gastric cancer.
Reducing Risk
Reducing the risk of developing cancer or the risk of recurrence
May have either a protective or damaging effect of reactive oxygen species on DNA, depending dose or on the concentration of chelating metal ions
Cautions
Quercetin is relatively nontoxic and is considered “possibly safe” orally in doses of 500 mg or less. However, quercetin can cause side effects and drug interactions.
Quercetin may interfere with the actions of some chemotherapy drugs. Consult with your pharmacist for interactions and discuss using quercetin with your doctor. See The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing, page 170, for a list of chemotherapy drugs that interact with quercetin and with which quercetin should not be taken.
In lab and animal studies, quercetin has shown worrisome effects, blocking cell death (apoptosis) in one lab study and worsening estrogen-induced breast tumors in one animal study.
Access
Quercetin is widely available in food sources and in supplements.
Dosing
BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated. Levels of active ingredients of natural products can vary widely between and even within products. See Quality and Sources of Herbs, Supplements and Other Natural Products.
Clinical trials have not established optimal quercetin dose during or after cancer treatment. Dosage recommendations are available from these sources:
Integrative Programs, Protocols and Medical Systems
Integrative oncology clinicians such as Keith Block, Dwight McKee and Lise Alschuler incorporate quercetin supplementation into care during active cancer treatment and/or in post-treatment care to prevent recurrence or secondary cancers.
- Programs and protocols
- Alschuler & Gazella complementary approaches
- Bastyr University Integrative Oncology Research Center protocol for stage IV breast cancer
- Block program
- Anti-inflammatory terrain modification
- Chemotherapy enhancement
- Natural molecular target modification
- Reduction of risk of secondary cancers
- Lemole, Mehta & McKee protocols
- MacDonald breast cancer program advises avoiding quercetin
- McKinney protocols
Integrative oncologist and BCCT advisor Dr. Keith Block uses quercetin as a natural molecular target modifier (IGF-I). Targeted therapies home in on particular growth pathways that cancer cells use to proliferate while sparing normal cells. Dr. Block also uses quercetin in multiple vitamin combinations, including with vitamin C to tackle inflammation alterations of the terrain of the human body. Quercetin may also help manage cancer-related and/or treatment-related symptoms such as diarrhea and depression. Please see Dr. Block's book for details: Life over Cancer: The Block Center Program for Integrative Cancer Treatment.
Non-cancer Uses of Quercetin
A 2017 review listed these effects and uses of quercetin:
- Treating allergies
- Preventing cardiovascular disease
- Treating chronic obstructive pulmonary disease (COPD)
- Treating neurodegenerative diseases
- Reducing systolic blood pressure and plasma oxidized LDL concentrations
- Treating ulcers and gastritis
- Treating bacterial and viral infections
BCCT has not reviewed the effectiveness of this therapy for non-cancer uses.
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Written by Laura Pole, RN, MSN, OCNS, and reviewed by Nancy Hepp, MS; most recent update August 21, 2019. Note: BCCT has not conducted an independent review of research of quercetin. This summary draws primarily from Memorial Sloan Kettering Cancer Center’s About Herbs and other sources as noted.
- Khan SI, Zhao J, Khan IA, Walker LA, Dasmahapatra AK. Potential utility of natural products as regulators of breast cancer-associated aromatase promoters. Reproductive Biology and Endocrinology. 2011 Jun 21;9:91.
- Yang F, Song L et al. Quercetin in prostate cancer: chemotherapeutic and chemopreventive effects, mechanisms and clinical application potential (Review). Oncology Reports. 2015 Jun;33(6):2659-68.
- Tummala R, Lou W, Gao AC, Nadiminty N. Quercetin targets hnRNPA1 to overcome enzalutamide resistance in prostate cancer cells. Molecular Cancer Therapeutics. 2017 Dec;16(12):2770-2779.
- Hashemzaei M, Delarami Far A et al. Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports. 2017 Aug;38(2):819-828.
- Yasuda MT, Sakakibara H, Shimoi K. Estrogen- and stress-induced DNA damage in breast cancer and chemoprevention with dietary flavonoid. Genes and Environment. 2017 Feb 1;39:10.
- Li S, Zhao Q et al. Quercetin reversed MDR in breast cancer cells through down-regulating P-gp expression and eliminating cancer stem cells mediated by YB-1 nuclear translocation. Phytotherapy Research. 2018 Aug;32(8):1530-1536; Li S, Yuan S et al. Quercetin enhances chemotherapeutic effect of doxorubicin against human breast cancer cells while reducing toxic side effects of it. Biomed Pharmacother. 2018 Apr;100:441-447.
- Iriti M, Kubina R et al. Rutin, a quercetin glycoside, restores chemosensitivity in human breast cancer cells. Phytotherapy Research. 2017 Oct;31(10):1529-1538.
- Chan MM, Fong D, Soprano KJ, Holmes WF, Heverling H. Inhibition of growth and sensitization to cisplatin-mediated killing of ovarian cancer cells by polyphenolic chemopreventive agents. Journal of Cellular Physiology. 2003 Jan;194(1):63-70.
- Aiyer HS, Warri AM, Woode DR, Hilakivi-Clarke L, Clarke R. Influence of berry polyphenols on receptor signaling and cell-death pathways: implications for breast cancer prevention. Journal of Agricultural and Food Chemistry. 2012 Jun 13;60(23):5693-708.
- Hashemzaei M, Delarami Far A et al. Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports. 2017 Aug;38(2):819-828.
- Yasuda MT, Sakakibara H, Shimoi K. Estrogen- and stress-induced DNA damage in breast cancer and chemoprevention with dietary flavonoid. Genes and Environment. 2017 Feb 1;39:10.
- Scambia G, Ranelletti FO et al. Quercetin potentiates the effect of adriamycin in a multidrug-resistant MCF-7 human breast-cancer cell line: P-glycoprotein as a possible target. Cancer Chemotherapy and Pharmacology. 1994;34(6):459-64; Wang G, Zhang J, Liu L, Sharma S, Dong Q. Quercetin potentiates doxorubicin mediated antitumor effects against liver cancer through p53/Bcl-xl. PLoS One. 2012;7(12):e51764.
- Block KI. Life Over Cancer. New York: Bantam Dell. 2009. p. 486.
- Iriti M, Kubina R et al. Rutin, a quercetin glycoside, restores chemosensitivity in human breast cancer cells. Phytotherapy Research. 2017 Oct;31(10):1529-1538.
- Haghi A, Azimi H, Rahimi R. A comprehensive review on pharmacotherapeutics of three phytochemicals, curcumin, quercetin, and allicin, in the treatment of gastric cancer. Journal of Gastrointestinal Cancer. 2017 Dec;48(4):314-320.
- Yasuda MT, Sakakibara H, Shimoi K. Estrogen- and stress-induced DNA damage in breast cancer and chemoprevention with dietary flavonoid. Genes and Environment. 2017 Feb 1;39:10; Griffiths K, Aggarwal BB et al. Food antioxidants and their anti-inflammatory properties: a potential role in cardiovascular diseases and cancer prevention. Diseases. 2016 Aug 1;4(3). pii: E28.
- TRC Natural Medicines Database. Quercetin: Monograph. Viewed December 28, 2017.
- Andres S, Pevny S et al. Safety aspects of the use of quercetin as a dietary supplement. Molecular Nutrition & Food Research. 2017 Nov 11.
- Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010. p. 170.
- Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010. p. 170.
- Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010; Alschuler LN, Gazella KA. The Definitive Guide to Thriving after Cancer: A Five-Step Integrative Plan to Reduce the Risk of Recurrence and Build Lifelong Health. Berkeley, California: Ten Speed Press. 2013.
- McKinney N. Naturopathic Oncology, 3rd Edition. Victoria, BC, Canada: Liaison Press. 2016. p. 316.
- Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009.
- Lemole G, Mehta P, McKee D. After Cancer Care: The Definitive Self-Care Guide to Getting and Staying Well for Patients with Cancer. New York, New York: Rodale, Inc. 2015.
- MacDonald B. The Breast Cancer Companion: A Complementary Care Manual: Third Edition. (self-published, Amazon, 2016).
- McKinney N. Naturopathic Oncology, 3rd Edition. Victoria, BC, Canada: Liaison Press. 2016.
- Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009. p. 525.
- Block KI. Life Over Cancer. New York: Bantam Dell. 2009. pp. 337 and 341.
- Block KI. Life over Cancer: The Block Center Program for Integrative Cancer Treatment. New York: Bantam Dell. 2009. p. 143; Memorial Sloan Kettering. About Herbs: Quercetin. December 6, 2016. viewed December 28, 2017.
- Anand David AV, Arulmoli R, Parasuraman S. Overviews of biological importance of quercetin: a bioactive flavonoid. Pharmacognosy Reviews. 2016 Jul-Dec;10(20):84-89.
View All References
More Information
- Memorial Sloan Kettering Cancer Center’s About Herbs: Quercetin
- TRC Natural Medicines website (subscription is required): in-depth information, ratings of effectiveness and safety and evaluation of specific quercetin products
- Consumer Labs: (subscription required): Quercetin
- Moss Reports (purchase required): Select from the list of cancers down the left side of the page for a report describing uses of conventional, complementary, alternative and integrative therapies related to that cancer. Ralph Moss is among the most knowledgeable and balanced researchers of integrative cancer therapies. The cost of his Moss Reports is not negligible, but many patients find them of considerable value. Moss is also available for consultations.
- Michael Lerner: Choices In Healing: Integrating the Best of Conventional and Complementary Approaches to Cancer
- Keith I. Block, MD: Life over Cancer: The Block Center Program for Integrative Cancer Treatment
- Lise Alschuler, ND, FABNO, and Karolyn Gazella: The Definitive Guide to Cancer, 3rd Edition
- Lone Star Medical Group: Natural Alternative Treatments
- Neil McKinney, BSc, ND: Naturopathic Oncology, 3rd Edition
- Donald I. Abrams, MD, and Andrew T. Weil, MD: Integrative Oncology, 2nd Edition
- Dwight McKee, MD, editor: Clinical Pearls
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