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Supplements

quercetin

What Is It?
Health Benefits
Forms
Dosage Information
Guidelines for Use
General Interaction
Possible Side Effects
Cautions
References
Evidence Based Rating Scale


What Is It? 

Quercetin may be a major reason why the old adage about eating "an apple a day" has been associated with good health. And why a daily cup of tea is more than a comforting ritual. Quercetin is primarily found in apples, onions, tomatoes, kale, broccoli, green beans, wine, berries, and tea: fruit skins typically have the greatest concentration of quercetin and they are partially responsible for the health benefits of wine. It is one of the most abundant of the flavonoids or plant pigments, and it is often a major source of a plant's medicinal activity. The most common form of quercetin is rutin, a glycoside that structurally is quercetin with a glucose molecule attached.(1)

Health Benefits

Quercetin appears to help fight a host of disorders, from asthma to cancer to heart disease. As an Antioxidant, it combats the destructive "free radical" molecules that play a part in many diseases. Quercetin also inhibits inflammation-producing enzymes and the release of histamine.

Studies involving quercetin's role in cancer prevention are conflicting. Among people with high dietary intakes of quercetin and other major flavonoids, population studies show that quercetin may reduce the risk of lung, pancreatic, and stomach cancers, particularly in male smokers. (2-4) However, a 2009 Women's Health Study did not find a major role for quercetin in cancer prevention in women over 45 years of age. (5)

Quercetin and other flavonoids may also help to prevent heart attacks. The Rotterdam Study, published in the 2002 American Journal of Clinical Nutrition, examined the tea-drinking habits and dietary flavonoid intakes of nearly 5,000 adults in Holland. Apparently, because of black tea’s high flavonoid concentration, daily consumption of the brew reduced the risk of heart attack overall. (6) A 2003 study found no association between quercetin and other flavonoids with reduced risk of cardiovascular disease overall in women. (7) However, a strong connection was found for reduced risk of fatal heart attack in women with high intake of dietary flavonoids although quercetin was not specifically mentioned. The researchers speculate that women's extra protection may be related to the flavonoids' role as phytoestrogens (plant estrogens), which can offer heart-protective benefits. Another study suggested that flavonoids increased bone density in women, a known action of phytoestrogens. (8)

Specifically, quercetin may help to:

  • Reduce cancer risk. Quercetin may help to reduce the risk of developing certain cancers. In one study, lung cancer was 58% lower among people who ate the most apples compared to those who ate the fewest. (9) Quercetin and other flavonoids have also been shown to help reduce the risk of pancreatic and stomach cancers. (2-4)

  • Prevent heart attack. One cause of heart disease is the overgrowth of smooth muscle cells in artery walls, a key component in the development of atherosclerosis. There is now evidence that quercetin functions to stop the overgrowth of cells that harm the heart. A 2002 study in the journal Surgery reported that in laboratory tests, quercetin arrested the development of vascular smooth muscle cells by locking them in a "no-growth" state. (10) This may help to explain findings of reduced heart attack risk in the Rotterdam Study.

  • Stave off cataracts. A lifetime of unprotected sun exposure can damage the eyes as well as the skin. It happens so gradually that many people aren't aware they're developing cataracts. Ultraviolet (UV) rays, particularly the burning UVB rays, damage proteins in the lens of the eye, causing them to clump together in a whitish cloud. Cigarette smoking and a deficiency in antioxidant vitamins are other major causes of cataracts. Research indicates that quercetin blocks aldose reductase, an Enzyme that leads to accumulation of sorbitol, a type of sugar that contributes to cataract formation, particularly in patients with diabetes. (1, 11-12)

  • Control asthma. Quercetin may be useful in relieving asthma (and possibly hay fever and sinusitis) as a result of its ability to reduce Inflammation in the airways and to prevent the release of Histamine, which contributes to congestion. (13-16) It appears to block allergic reactions to pollen as well.

  • Maintain health when suffering from Crohn's disease. Quercetin, a natural anti-inflammatory, may be helpful in countering the hallmark of Crohn's disease: chronic inflammation of the gastrointestinal tract. Crohn's manifests as abdominal pain, fever, diarrhea, and weight loss. The small intestine is primarily affected and problems in absorbing important nutrients develop. Conventional physicians use the anti-inflammatory drugs sulfasalazine and steroids to reduce the inflammation; taking quercetin is one (natural) way to supplement the actions of these drugs. (17, 18)

  • Prevent recurrent gout attacks. Taken with cherry fruit Extract (as well as fresh or canned cherries), Vitamin C, and possibly fish oils, quercetin may do the trick in forestalling acute attacks by lowering elevated uric acid levels--the cause of painful gout attacks. (19) The combination can be taken on a long-term basis.

  • Speed up healing of recurrent heartburn, or gastroesophageal reflux disorder (GERD). As a flavonoid, quercetin functions as a natural anti-inflammatory, Antihistamine, and possibly an inhibitor of Helicobacter pylori, the bacterium associated with stomach ulcers, which can cause recurrent heartburn. (20) If your heartburn symptoms are persistent, you may want to take a daily combination of quercetin and flavonoids to accelerate healing.

  • Reduce blood pressure. Animal studies indicate quercetin gives progressive, sustained, dose-dependent reduction in blood pressure in hypertensive rats and rats with metabolic syndrome. And in one human study, high doses of quercetin reduced blood pressure in patients with hypertension. More human studies are needed to determine if quercetin lowers blood pressure enough to be clinically significant. (21)

  • Benefit prostate problems. Studies indicate quercetin may ease the pain associated with prostatitis—an inflammation of the prostate gland. However, the supplement did not appear to affect voiding dysfunction in men with chronic, nonbacterial prostatitis. (22)

Forms

  • tablet
  • capsule

Dosage Information

Special tips:
--Quercetin is often paired with bromelain, a natural anti-inflammatory derived from pineapples. See the entry on
bromelain/quercetin in the WholeHealthMD reference library

To reduce cancer risk: Take 125-250 mg daily.

To prevent heart attack: Take 125-250 mg daily.

To prevent cataracts: Take 125-250 mg daily.

For asthma: Take 250-500 mg 3 times a day.

For Crohn's disease: Take 400 mg 3 times a day.

For recurrent gout attacks: Take 500 mg twice a day.

For heartburn: Take 500 mg three times a day of quercetin or mixed bioflavonoids (with or without added bromelain).

Guidelines for Use

  • For those who cannot drink red wine for its heart-protecting benefits, quercetin capsules may constitute an effective alternative.

  • When possible, take quercetin in combination with vitamin C; the flavonoid enhances the vitamin's effect.

General Interaction

  • Quercetin competitively binds to sites on bacteria where the quinolone antibiotics work potentially reducing the efficacy of ciproflaxin (Cipro), levofloxacin (Levaquin), moxifloxacin (Avelox), and others.

  • The clearance of most drugs that are metabolized in the liver may be slowed by quercetin allowing drug levels to become higher than usual with potentially increased effects or toxicity. Check with your pharmacist or physician regarding prescription drugs you are taking.

Possible Side Effects

Quercetin in supplement form can cause tingling in the extremities and headaches.  

Cautions

There are no known cautions associated with quercetin.

References

1. Quercetin. Altern Med Rev. 1998 Apr;3(2):140-3.
2. Nöthlings U, Murphy SP, Wilkens LR, et al. Flavonols and pancreatic cancer risk: the multiethnic cohort study. Am J Epidemiol 2007;166:924-31.
3. Bobe G, Weinstein SJ, Albanes D, et al. Flavonoid intake and risk of pancreatic cancer in male smokers (Finland). Cancer Epidemiol Biomarkers Prev 2008;17:553-62.
4.  Garcia-Closas R, Gonzalez CA, Agudo A, Riboli E. Intake of specific carotenoids and flavonoids and the risk of gastric cancer in Spain. Cancer Causes Control. 1999 Feb;10(1):71-5.
5. Wang L, Lee IM, Zhang SM, Blumberg JB, Buring JE, Sesso HD. Dietary intake of selected flavonols, flavones, and flavonoid-rich foods and risk of cancer in middle-aged and older women. Am J Clin Nutr. 2009 Mar;89(3):905-12.
6. Geleijnse JM, Launer LJ, Van der Kulp DA, et al. Inverse association of tea and flavonoid intakes with incident myocardial infarction: the Rotterdam Study. Am J Clin Nutr. 2002 May;75(5):880-6.
7. Sesso HD, Gaziano JM, Liu S, Buring JE. Flavonoid intake and the risk of cardiovascular disease in women. Am J Clin Nutr. 2003 Jun;77(6):1400-8.
8. Lissin LW, Cooke JP. Phytoestrogens and cardiovascular health. J Am Coll Cardiol. 2000 May;35(6):1403-10.
9. Arts IC, Hollman PC, Bueno De Mesquita HB, et al. Dietary catechins and epithelial cancer incidence: the Zutphen elderly study. Int J Cancer. 2001 Apr 15;92(2):298-302.
10. Alcocer F, Whitley D, Salazar-Gonzalez JF, et al. Quercetin inhibits human vascular smooth muscle cell proliferation and migration. Surgery. 2002 Feb;131(2):198-204.
11. Varma SD, Mikuni I, Kinoshita JH. Flavonoids as inhibitors of lens aldose reductase. Science. 1975 Jun 20;188(4194):1215-6.
12. Varma SD, Mizuno A, Kinoshita JH. Diabetic cataracts and flavonoids. Science. 1977 Jan 14;195(4274):205-6.
13. Middleton E Jr, Drzewieki G. Flavonoid inhibition of human basophil histamine release stimulated by various agents. Biochem Pharmacol. 1984;33:3333-8.
14. Amella M, Bronner C, Briancon F, et al. Inhibition of mast cell histamine release by flavonoids and bioflavonoids. Planta Med. 1985;51:16-20.
15. Pearce FL, Befus AD, Bienenstock J. Mucosal mast cells. III. Effect of quercetin and other flavonoids on antigen-induced histamine secretion from rat intestinal mast cells. J Allergy Clin Immunol. 1984;73:819-23.
16. Busse WW, Kopp DE, Middleton E Jr. Flavonoid modulation of human neutrophil function. J Allergy Clin Immunol. 1984;73:801-9.
17. Mizoyama Y, Takaki H, Sugihara N, Furuno K. Inhibitory effect of flavonoids on N-acetylation of 5-aminosalicylic acid in cultured rat hepatocytes. Biol Pharm Bull. 2004 Sep;27(9):1455-8.

18. Hering NA, Schulzke JD. Therapeutic options to modulate barrier defects in inflammatory bowel disease. Dig Dis. 2009;27(4):450-4.

19. Zhu JX, Wang Y, Kong LD, et al. Effects of Biota orientalis extract and its flavonoid constituents, quercetin and rutin on serum uric acid levels in oxonate-induced mice and xanthine dehydrogenase and xanthine oxidase activities in mouse liver. J Ethnopharmacol. 2004 Jul;93(1):133-40.

20. Kahraman A, Erkasap N, KoKen T, et al. The antioxidative and antihistaminic properties of quercetin in ethanol-induced gastric lesions. Toxicology. 2003 Feb 1;183(1-3):133-42.

21. Perez-Vizcaino F, Duarte J, Jimenez R, Santos-Buelga C, Osuna A. Antihypertensive effects of the flavonoid quercetin. Pharmacol Rep. 2009 Jan-Feb;61(1):67-75.

 

22. Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men with category III chronic prostatitis: a preliminary prospective, double-blind, placebo-controlled trial. Urology. 1999 Dec;54(6):960-3.

 

23. Choi JS, Choi BC, Choi KE. Effect of quercetin on the pharmacokinetics of oral cyclosporine. Am J Health Syst Pharm 2004;61:2406-9

 
 
 
 
 
 
 
 
 
 
 
 

Evidence Based Rating Scale  

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies and what our clinical advisors have found to be efficacious in their personal practice into a visual and easy to interpret format. This tool is meant to simplify the information on supplements and therapies that demonstrate promise in the treatment of certain conditions.

 

Condition

Rating

Explanation

 

Asthma

   

May have benefit in reducing the inflammation response in the lungs. More studies are needed to confirm or refute this finding. (13-16)

Cancer Prevention,  
Studies indicate quercetin may reduce risk of lung, pancreatic, and stomach cancer; more studies needed. (1-5)
Cataracts  
Studies indicate quercetin may block enzyme that causes cataract formation. (1,11-12)


Crohn's Disease  
Preliminary animal studies have shown efficacy as a complement to conventional medications. Human trials are needed to confirm these results. (17-18)
 Gout Date Published: 04/19/2005
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