Quercetin
 Authors
Laura Pole, RN, MSN, OCNS, BCCT Senior Researcher
Read more Ms. Pole is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation and education services for more than 30 years. View profile.  Nancy Hepp, MS, BCCT Project Manager
Read more Ms. Hepp is a science researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. View profile. Last updated February 16, 2021.
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Also known by these names
- Polyphenolic flavonoid
- 3,3',4',5,7-pentapentahydroxyflavone
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Key Points
- Before using this therapy, consult your oncology team about interactions with other treatments and therapies. Also make sure this therapy is safe for use with any other medical conditions you may have.
- 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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- Killed cancer cells or prevented cancer cells from growing
- May increase cancer cell sensitivity to topotecan and gemcitabine.
- Either promoted or blocked cell death (apoptosis) or promoted or reduced tumor growth in preclinical studies, depending on dose
- Breast cancer:
- Induced cell death (apoptosis) in cell studies and reduced tumor volume in mice bearing estrogen receptor‑positive breast cancer cells.
- 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
- Induced cell death (apoptosis ) in cell studies and reduced tumor volume in mice bearing estrogen receptor‑positive breast cancer cells.
- Sensitized resistant breast cancer cells to doxorubicin
- Reversed multidrug resistance and restored chemosensitivity to cyclophosphamide and cyclophosphamide of human chemoresistant, triple-negative breast cancer cells with rutin, a quercetin glycoside
- Sensitized cells to radiotherapy
- Colorectal cancer: Induced cell death (apoptosis) in colon cancer cells
- Liver cancer: Sensitized resistant liver cancer cells to doxorubicin
- Ovarian cancer: Increased sensitivity of ovarian cancer cells to cisplatin when used in combination with curcumin
- Prostate cancer:
- Inhibited prostate cancer growth in animal studies.
- Resensitized enzalutamide-resistant prostate cancer cells to enzalutamide treatment in mouse xenografts.
- Stomach cancer: promoted activity to fight Helicobacter pylori (H. pylori) infection, which is associated with an increased risk of stomach (gastric cancer)
Managing Side Effects and Promoting Wellness
Clinical Evidence
- Reduced fatigue and other common side effects of sunitib when isoquercetin was used with vitamin C and vitamin B3 among people with kidney cancer
Lab and Animal Evidence
Read more
- Protected cells from radiation damage, mainly by reducing cellular stress
Reducing Risk
Reducing the risk of developing cancer or the risk of recurrence
- Reduced risk of all cancers combined, breast and ovarian cancers with high dietary intake of quercetin or of flavanols including quercetin
- No reduced risk of ovarian cancer was found at at levels commonly consumed in a typical diet.
- Reduced risk of colorectal cancer in epidemiological and case-control studies with increasing intake of quercetin or of flavanols including quercetin
- Reduced risk of lung cancer in epidemiological studies
- Reduced risk of smoking-related cancers (lung cancer and aerodigestive tract cancer such as oral and esophageal cancers) in smokers, but not nonsmokers
Optimizing Your Terrain
- Quercetin either increased or decreased aromatase enzyme activity in adrenocortical carcinoma cells, depending on dose.
- uppressed tumor-promoting responses in breast cancer cells.
- No impact on markers of inflammation
- 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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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.
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- 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.
- 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.
- Buonerba C, De Placido P et al. Isoquercetin as an adjunct therapy in patients with kidney cancer receiving first-line sunitinib (QUASAR): results of a phase I trial. Frontiers in Pharmacology. 2018 Mar 16;9:189.
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- TRC Natural Medicines Database. Quercetin: Monograph. Viewed December 28, 2017.
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- 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.
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- 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).
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- 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.
- Gurdev Parmar and Tina Kaczor: Textbook of Naturopathic Oncology
- Dwight McKee, MD, editor: Clinical Pearls
- Donald I. Abrams, MD, and Andrew T. Weil, MD: Integrative Oncology, 2nd Edition
- Neil McKinney, BSc, ND: Naturopathic Oncology, 3rd Edition
- Lise Alschuler, ND, FABNO, and Karolyn Gazella: The Definitive Guide to Cancer, 3rd Edition
- Keith I. Block, MD: Life over Cancer: The Block Center Program for Integrative Cancer Treatment
- Lone Star Medical Group: Natural Alternative Treatments
- Michael Lerner: Choices In Healing: Integrating the Best of Conventional and Complementary Approaches to Cancer
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