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Quercetin
Overview
Quercetin belongs to a group of plant pigments called flavonoids that give many fruits, flowers, and vegetables their color.
Flavonoids such as quercetin are antioxidants -- they scavenge damaging particles in the body known as free radicals, which damage cell membranes, tamper with DNA, and even cause cell death. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause. They also help keep LDL ("bad") cholesterol from being damaged, which scientists think may contribute to heart disease. In test tubes, quercetin has strong antioxidant properties, but researchers aren't sure whether taking quercetin (and many other antioxidants) has the same effects inside the body.
Quercetin acts like an antihistamine and an anti-inflammatory, and may help protect against heart disease and cancer.


What is Quercetin ?
Quercetin is a bioflavonoid common in the plant kingdom, especially high in onions, red wine, and green tea. It is one of the most biologically active bioflavonoids. Quercetin acts as a potent polyphenol antioxidant and immune system modulator. Many of its immune support attributes are enhanced by its synergistic relationship with vitamin C. Quercetin is highly active in the skin and lining of the digestive tract.

Where it is found
Fruits and vegetables -- particularly citrus fruits, apples, onions, parsley, tea, and red wine -- are the primary dietary sources of quercetin. Olive oil, grapes, dark cherries, and dark berries -- such as blueberries, blackberries, and bilberries -- are also high in flavonoids, including quercetin.
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Benefits / uses
Allergies, Asthma, Hay Fever and Hives
In test tubes, quercetin prevents immune cells from releasing histamines, chemicals that cause allergic reactions. On that basis, researchers think quercetin helps reduce symptoms of allergies, including runny nose, watery eyes, hives, and swelling of the face and lips.

Heart Disease
Studies suggest that the flavonoids quercetin, resveratrol, and catechins (all found in high concentration in red wine) may help reduce the risk of atherosclerosis (plaque build up in arteries that can lead to heart attack or stroke). These nutrients appear to protect against the damage caused by LDL ("bad") cholesterol and may help prevent death from heart disease. However, most human studies have looked at flavonoids in the diet, not as supplements.

High Cholesterol
Test tubes studies show that quercetin prevents damage to LDL cholesterol, and population studies show that people who eat diets high in flavonoids have lower cholesterol. One study found that people who took quercetin and an alcohol-free red wine extract (which contains quercetin) had less damage to LDL cholesterol.

Hypertension
Studies show that quercetin supplementation reduces blood pressure in people who have hypertension.

Interstitial Cystitis
Two small studies suggested that people with interstitial cystitis might benefit from flavonoids. People with this condition have bladder pain, similar to a bladder infection, and often experience an urgent need to urinate. In both studies, those who took a supplement containing quercetin appeared to have fewer symptoms.

Prostatitis
Some preliminary evidence indicates that quercetin might reduce symptoms of prostatitis (inflammation of the prostate). One small study found that men who took quercetin had a reduction in symptoms compared to men who took placebo.

Rheumatoid Arthritis (RA)
There are reports of people with RA who had fewer symptoms when they switched from a typical Western diet to a vegan diet with lots of uncooked berries, fruits, vegetables, nuts, roots, seeds, and sprouts containing antioxidants, including quercetin..

Cancer
Quercetin and other flavonoids contained in fruits and vegetables. Scientists have long considered important in cancer prevention. People who eat more fruits and vegetables tend to have lower risk of some types of cancer. And animal and test-tube studies suggest that flavonoids do indeed have anti-cancer properties. Quercetin and other flavonoids have been shown in these studies to inhibit the growth of cancer cells from breast, colon, prostate, ovarian, endometrial, and lung tumors.

Doses
Recommended adult dosages of quercetin vary depending on the condition being treated. The following are guidelines:

arw General supplementation: 100 - 250 mg 3 times per day


arw Allergy symptoms: 250 - 600 mg per day divided in several doses


arw Chronic prostatitis: 500 mg 2 times per day


arw Interstitial cystitis: 500 mg 2 times per day

Possible Side effects / Precautions / Possible Interactions:
If you are being treated with any of the following medications, you should not use quercetin supplements without first talking to your health care provider.

Anticoagulants (blood thinners) -- Quercetin may enhance the effect of these drugs, increasing your risk for bleeding:
Warfarin (Coumadin)
Clopidogrel (Plavix)
Aspirin
Chemotherapy -- Test tube and animal studies suggest that quercetin may enhance the effects of doxorubicin and cisplatin, two chemotherapy medications used to treat cancer. In addition, some doctors believe taking antioxidants at the same time as chemotherapy can be harmful, while others believe it can be helpful. Talk to your oncologist before taking any supplements if you are undergoing chemotherapy.
Corticosteroids -- Quercetin may cause these drugs to stay in the body longer.
Cyclosporine -- Quercetin may interfere with the body's absorption of this drug, which is used to suppress the immune system.

Research studies / References

arw a b Laura K. Stewart, Jeff L. Soileau, David Ribnicky, Zhong Q. Wang, Ilya Raskin, Alexander Poulev, Martin Majewski, William T. Cefalu, and Thomas W. Gettys (2008). "Quercetin transiently increases energy expenditure but persistently decreases circulating markers of inflammation in C57BL/6J mice fed a high-fat diet". Metabolism 57.


arw a b c J. Mark Davis, E. Angela Murphy, Martin D. Carmichael, and Ben Davis (2009), "Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance", Am J Physiol Regul Integr Comp Physiol 296


arw Phys Ed: Is Quercetin Really a Wonder Sports Supplement? By Gretchen Reynolds. New York Times, October 7, 2009. Review of the research.


arw American Cancer Society, Quercetin


arw "Guidance for Industry: A Food Labeling Guide XI. Appendix C: Health Claims, 21 CFR 101.76 and 21 CFR 101.78, April 2008". US Department of Health and Human Services, Food and Drug


arw Administration.
http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodLabelingNutrition/FoodLabelingGuide/ucm064919.htm.


arw Neuhouser ML (2004). "Dietary flavonoids and cancer risk: evidence from human population studies". Nutr Cancer 50 (1): 1-7. doi:10.1207/s15327914nc5001_1. PMID 15572291.


arw Murakami A, Ashida H, Terao J (October 2008). "Multitargeted cancer prevention by quercetin". Cancer Lett. 269 (2): 315-25. doi:10.1016/j.canlet.2008.03.046. PMID 18467024.


arw Verschoyle RD, Steward WP, Gescher AJ (2007). "Putative cancer chemopreventive agents of dietary origin-how safe are they?". Nutr Cancer 59 (2): 152-62. doi:10.1080/01635580701458186 (inactive 2009-06-26). PMID 18001209.


arw Rietjens IM, Boersma MG, van der Woude H, Jeurissen SM, Schutte ME, Alink GM (July 2005). "Flavonoids and alkenylbenzenes: mechanisms of mutagenic action and carcinogenic risk". Mutat. Res. 574 (1-2): 124-38. doi:10.1016/j.mrfmmm.2005.01.028. PMID 15914212.


arw van der Woude H, Alink GM, van Rossum BE, et al. (December 2005). "Formation of transient covalent protein and DNA adducts by quercetin in cells with and without oxidative enzyme activity". Chem. Res. Toxicol. 18 (12): 1907-16. doi:10.1021/tx050201m. PMID 16359181.


arw US FDA, Center for Food Safety and Nutrition, Qualified Health Claims Subject to Enforcement Discretion, April 2007 [1][dead link]


arw Clinicaltrials.gov, National Institutes of Health


arw USDA Database for the Flavonoid Content of Selected Foods


arw Crystal Smith, Kevin A. Lombard, Ellen B. Peffley, Weixin Liu (2003). "Genetic Analysis of Quercetin in Onion (Allium cepa L.) Lady Raider". The Texas Journal of Agriculture and Natural Resource (Agriculture Consortium of Texas) 16: 24-8. Archived from the original on February 25, 2007. http://web.archive.org/web/20070225125621/http%3A//www.tarleton.edu/%7Etxjanr/2003issue/article3.pdf.


arw Sari H. Häkkinen et al. (1999). "Content of the Flavonols Quercetin, Myricetin, and Kaempferol in 25 Edible Berries". Journal of Agricultural and Food Chemistry 47 (6): 2274-9. doi:10.1021/jf9811065. PMID 10794622.


arw A. E. Mitchell, Y. J. Hong, E. Koh, D. M. Barrett, D. E. Bryant, R. F. Denison and S. Kaffka (2007). "Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes". Journal of Agricultural and Food Chemistry 55 (15): 6154-9. doi:10.1021/jf070344. PMID 17590007.


arw Honey Research Unit


arw honey fingerprinting
  Biosynthesis of quercetin.


arw Winkel-Shirley, Brenda (June 2001). "Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology". Plant Physiol 126 (2): 485-493. doi:10.1104/pp.126.2.485. PMC 1540115. PMID 11402179. http://www.plantphysiol.org/cgi/content/full/126/2/485.


arw Paliwal S; Sundaram, J; Mitragotri, S (2005). "Induction of cancer-specific cytotoxicity towards human prostate and skin cells using quercetin and ultrasound". British Journal of Cancer 92 (3): 499-502. doi:10.1038/sj.bjc.6602364. PMC 2362095. PMID 15685239. http://www.nature.com/bjc/journal/v92/n3/abs/6602364a.html.


arw Edwards RL, Lyon T, Litwin SE, Rabovsky A, Symons JD, Jalili T (1 November 2007). "Quercetin reduces blood pressure in hypertensive subjects". J. Nutr. 137 (11): 2405-11. PMID 17951477. http://jn.nutrition.org/cgi/pmidlookup?view=long&pmid=17951477.


arw Egert S et al. (2009). "Quercetin reduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects with a high-cardiovascular disease risk phenotype: A double-blinded, placebo-controlled cross-over study". Br J Nutr 102 (7): 1065-1074. PMID 19402938.
24. Nöthlings U et al. (2007). "Flavonols and pancreatic cancer risk". American Journal of Epidemiology 166 (8): 924-931. doi:10.1093/aje/kwm172. PMID 17690219.


arw Davis JM, Murphy EA, Carmichael MD, Davis B. (2009). "Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance.". Am J Physiol Regul Integr Comp Physiol. 296 (4): R1071-7. doi:10.1152/ajpregu.90925.2008. PMID 19211721.


arw Yang JY, Della-Fera MA, Rayalam S, Ambati S, Hartzell DL, Park HJ, Baile CA (2008). "Enhanced inhibition of adipogenesis and induction of apoptosis in 3T3-L1 adipocytes with combinations of resveratrol and quercetin". Life Sci. 82 (19-20): 1032-9. doi:10.1016/j.lfs.2008.03.003. PMID 18433793.


arw Papaliodis D, Boucher W, Kempuraj D, Theoharides TC (2008). "The flavonoid luteolin inhibits niacin-induced flush". Brit J Pharmacol 153 (7): 1382-87. doi:10.1038/sj.bjp.0707668. PMC 2437911. PMID 18223672.


arw Mullen W et al. (December 2008). "Bioavailability of [2-(14)C]quercetin-4'-glucoside in rats.". J Agric Food Chem. 2456 (24): 12127-37. doi:10.1021/jf802754s. PMID 19053221.


arw Hilliard JJ, Krause HM, Bernstein JI, et al. (1995). "A comparison of active site binding of 4-quinolones and novel flavone gyrase inhibitors to DNA gyrase". Adv. Exp. Med. Biol. 390: 59-69. PMID 8718602.


arw Si Dayong, Wang Y, Zhou Y-H, Guo Y, Wang J, Zhou H, Li Z-S, Fawcett JP (March 2009). "Mechanism of CYP2C9 inhibition by flavones and flavonols". Drug Metabolism and Disposition 37 (3): 629-634.. doi:10.1124/dmd.108.023416. PMID 19074529. http://p4502c.googlepages.com/dmd2.pdf


arw Su-Lan Hsiu; Yu-Chi Hou; Yao-Horng Wang; Chih-Wan Tsao; Sheng-Fang Sue; and Pei-Dawn L. Chao (6 December 2002). "Quercetin significantly decreased cyclosporin oral bioavailability in pigs and rats". Life Sciences 72 (3): 227-235. doi:10.1016/S0024-3205(02)02235-X. PMID 12427482.


arw Judy L. Raucy (1 May 2003). "Regulation of CYP3A4 Expression in Human Hepatocytes by Pharmaceuticals and Natural Products". Drug Metabolism and Disposition 31 (3): 533-539. doi:10.1124/dmd.31.5.533. PMID 12695340.