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Quercetin

Quercetin

Uses

What Are Star Ratings?

Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.

2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.

1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

This supplement has been used in connection with the following health conditions:

Used for Why
3 Stars
Prostatitis
1,000 mg daily
Quercetin has anti-inflammatory and antioxidant effects and may reduce symptoms of chronic prostatitis.

Quercetin , a flavonoid with anti-inflammatory and antioxidant effects, has recently been reported to improve symptoms of NBP and PD. An uncontrolled study reported that 500 mg of quercetin twice daily for at least two weeks significantly improved symptoms in 59% of men with chronic prostatitis.1 These results were confirmed in a double-blind study, in which similar treatment with quercetin for one month improved symptoms in 67% of men with NBP or PD.2 Another uncontrolled study combined 1,000 mg per day of quercetin with the enzymes bromelain and papain , resulting in significant improvement of symptoms.3 Bromelain and papain promote absorption of quercetin and have anti-inflammatory effects as well.4

2 Stars
Athletic Performance and Post-Exercise Infection
500 mg twice a day
In one study, quercetin lowered the incidence of upper respiratory tract infections in athletes following intensive exercise.
In a double-blind study of trained athletes, the incidence of upper respiratory tract infections following a three-day period of intensive exercise was significantly lower in people who took quercetin than in those who received a placebo (5% versus 45%).5 The amount of quercetin used was 500 mg twice a day, beginning three weeks before, and continuing for two weeks after, the intensive exercise.
1 Star
Allergies and Sensitivities
Refer to label instructions
Test tube and animal studies have found some effects from natural antihistamines such as the flavonoid quercetin, though no clinical research has shown whether these substances can specifically reduce allergic reactions.

Many of the effects of allergic reactions are caused by the release of histamine, which is the reason antihistamine medication is often used by allergy sufferers. Some natural substances, such as vitamin C 6 , 7 and flavonoids ,8 including quercetin ,9 , 10 have demonstrated antihistamine effects in test tube, animal, and other preliminary studies. However, no research has investigated whether these substances can specifically reduce allergic reactions in humans.

1 Star
Asthma
Refer to label instructions
Quercetin, a flavonoid found in many plants, has an inhibiting action on lipoxygenase, an enzyme that contributes to problems with asthma.

Quercetin , a flavonoid found in most plants, has an inhibiting action on lipoxygenase, an enzyme that contributes to problems with asthma.11 No clinical trials in humans have confirmed whether quercetin decreases asthma symptoms. Some doctors are currently experimenting with 400 to 1,000 mg of quercetin three times per day.

1 Star
Atherosclerosis
Refer to label instructions
Quercetin, a flavonoid, protects LDL cholesterol from damage.

Quercetin , a flavonoid , protects LDL cholesterol from damage.12 While several preliminary studies have found that eating foods high in quercetin lowers the risk of heart disease,13 , 14 , 15 the research on this subject is not always consistent,16 and some research finds no protective link.17 Quercetin is found in apples, onions, black tea, and as a supplement. In some studies, dietary amounts linked to protection from heart disease are as low as 35 mg per day.

1 Star
Cataracts
Refer to label instructions
The flavonoid quercetin may help protect against cataracts by blocking sorbitol accumulation in the eye.

The flavonoid quercetin may also help by blocking sorbitol accumulation in the eye.18 This may be especially helpful for people with diabetes , though no clinical trials have yet explored whether quercetin actually prevents diabetic cataracts.

1 Star
Childhood Diseases
Refer to label instructions
Quercetin is a flavonoid that has shown particularly strong antiviral properties in the test tube.

Flavonoids are a group of compounds found in some plant foods and medicinal herbs. An antiviral action of some flavonoids has been observed in a number of test tube experiments.19 , 20 , 21 , 22 , 23 Quercetin , one of the flavonoids, has shown particularly strong antiviral properties in the test tube;24 , 25 , 26 however, one study did not find quercetin to be of benefit to mice with a viral infection.27 It is not known whether flavonoids can be absorbed in amounts sufficient to exert an antiviral effect in humans, and therefore their possible role in the treatment of childhood exanthems remains unknown.

1 Star
Edema
Refer to label instructions
In one study, the flavonoid quercetin corrected abnormal capillary permeability (leakiness), an effect that might improve edema.
Because coumarin, hydroxyethylrutosides, and diosmin are not widely available in the United States, other flavonoids, such as quercetin, rutin, or anthocyanosides (from bilberry), have been substituted by doctors in an attempt to obtain similar benefits. The effect of these other flavonoids against edema has not been well studied. Also, optimal amounts are not known. However, in one study, quercetin in amounts of 30-50 mg per day corrected abnormal capillary permeability (leakiness),28 an effect that might improve edema. A similar effect has been reported with rutin at 20 mg three times per day.29 Doctors often recommend 80-160 mg of a standardized extract of bilberry, three times per day.
1 Star
Gout
Refer to label instructions
In test tube studies, quercetin, a flavonoid, has inhibited an enzyme involved in the development of gout.

In test tube studies, quercetin , a flavonoid , has inhibited an enzyme involved in the development of gout.30 , 31 However, it is not known whether taking quercetin by mouth can produce high enough quercetin concentrations in the body to achieve these effects. Although human research is lacking, some doctors recommend 150–250 mg of quercetin three times per day (taken between meals).

1 Star
Hay Fever
Consult a qualified healthcare practitioner
Quercetin is an increasingly popular treatment for hay fever.

Quercetin is an increasingly popular treatment for hay fever even though only limited preliminary clinical research has suggested that it is beneficial to hay fever sufferers.32

1 Star
Type 1 Diabetes
Refer to label instructions
Quercetin may be helpful for its ability to reduce levels of sorbitol—a sugar that accumulates in cells and damages the nerves, kidneys, and eyes of people with diabetes.
Doctors have suggested that quercetin might help people with diabetes because of its ability to reduce levels of sorbitol—a sugar that accumulates in nerve cells, kidney cells, and cells within the eyes of people with diabetes and has been linked to damage to those organs.33 Clinical trials have yet to explore whether quercetin actually protects people with diabetes from nerve damage (neuropathy), nephropathy, or eye damage ( retinopathy ).
1 Star
Type 2 Diabetes
Refer to label instructions
Quercetin may be helpful for its ability to reduce levels of sorbitol—a sugar that accumulates in cells and damages the nerves, kidneys, and eyes of people with diabetes.
Doctors have suggested that quercetin might help people with diabetes because of its ability to reduce levels of sorbitol—a sugar that accumulates in nerve cells, kidney cells, and cells within the eyes of people with diabetes—and has been linked to damage to those organs.34 Clinical trials have yet to explore whether quercetin actually protects people with diabetes from neuropathy, nephropathy, or retinopathy .

How It Works

How to Use It

Some doctors recommend 200–500 mg of quercetin taken two to three times per day. Optimal intake remains unknown.

Where to Find It

Quercetin can be found in onions, apples, green tea , and black tea. Smaller amounts are found in leafy green vegetables and beans.

Possible Deficiencies

No clear deficiency of quercetin has been established.

Interactions

Interactions with Supplements, Foods, & Other Compounds

Since flavonoids help protect and enhance vitamin C , quercetin is often taken with vitamin C.

Interactions with Medicines

Certain medicines interact with this supplement.

Types of interactions: Beneficial Adverse Check

Replenish Depleted Nutrients

  • none

Reduce Side Effects

  • none

Support Medicine

  • none

Reduces Effectiveness

  • none

Potential Negative Interaction

  • Estradiol

    Studies have shown that grapefruit juice significantly increases estradiol levels in the blood.35 , 36 One of the flavonoids found in grapefruit juice is quercetin. In a test tube study, quercetin was found to change estrogen metabolism in human liver cells in a way that increases estradiol levels and reduces other forms of estrogen.37 This effect is likely to increase estrogen activity in the body. However, the levels of quercetin used to alter estrogen metabolism in the test tube were much higher than levels found in the body after supplementing with quercetin.

    There is evidence from test tube studies that another flavonoid in grapefruit juice, naringenin, also has estrogenic activity.38 It has yet to be shown that dietary or supplemental levels of quercetin (or naringenin) could create a significant problem.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Felodipine

    Quercetin is a flavonoid found in grapefruit juice, tea, onions, and other foods; it is also available as a nutritional supplement. Quercetin has been shown in test tube studies to inhibit enzymes responsible for breaking down felodipine into an inactive form.39 This interaction may result in increased blood levels of felodipine that could lead to unwanted side effects. Until more is known about this interaction, patients taking felodipine should avoid supplementing with quercetin.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.

Explanation Required

  • Cyclosporine

    In an animal study, oral administration of quercetin (50 mg per 2.2 pounds of body weight) at the same time as cyclosporine decreased the absorption of cyclosporine by 43%.40 However, in a study of healthy human volunteers, supplementing with quercetin along with cyclosporine significantly increased blood levels of cyclosporine, when compared with administering cyclosporine alone.41 Because the effect of quercetin supplementation on cyclosporine absorption or utilization appears to be unpredictable, individuals taking cyclosporine should not take quercetin without the supervision of a doctor.

The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Side Effects

No clear toxicity has been identified. Early quercetin research suggested that large amounts of quercetin could cause cancer in animals.42 Most,43 , 44 , 45 but not all,46 current research finds quercetin to be safe or actually linked to protection from cancer.

Quercetin has been shown to cause chromosomal mutations in certain bacteria in test tube studies.47 Although the significance of this finding for humans is not clear, some doctors are concerned about the possibility that birth defects could occur in the offspring of people supplementing with quercetin at the time of conception or during pregnancy .

References

1. Shoskes DA. Use of the bioflavonoid quercetin in patients with longstanding chronic prostatitis. JANA 1999;2:36–9.

2. 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; 54:960–3.

3. 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; 54:960–3.

4. Izaka K, Yamada M, Kawano T, Suyama T. Gastrointestinal absorption and anti-inflammatory effect of bromelain. Jpn J Pharmacol 1972;22:519–34.

5. Nieman DC, Henson DA, Gross SJ, et al. Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc 2007;39:1561–9.

6. Johnston CS, Retrum KR, Srilakshmi JC. Antihistamine effects and complications of supplemental vitamin C. J Am Diet Assoc 1992;92:988–9.

7. Johnston S, Martin LJ, Cai X. Antihistamine effect of supplemental ascorbic acid and neutrophil chemotaxis. J Am Coll Nutr 1992;11:172–6.

8. Gabor M. Anti-inflammatory and anti-allergic properties of flavonoids. Prog Clin Biol Res 1986;213:471–80 [review].

9. Middleton E, Drzewieki G. Naturally occurring flavonoids and human basophil histamine release. Int Arch Allergy Appl Immunol 1985;77:155–7.

10. Amella M, Bronner C, Briancon F, et al. Inhibition of mast cell histamine release by flavonoids and bioflavonoids. Planta Medica 1985;51:16–20.

11. Welton AF, Tobias LD, Fiedler-Nagy C, et al. Effect of flavonoids on arachidonic acid metabolism. Prog Clin Biol Res 1986;213:231–42.

12. Ronzio RA. Antioxidants, nutraceuticals and functional foods. Townsend Letter for Doctors and Patients 1996;Oct:34–5 [review].

13. Hertog MGL, Feskens EJM, Hollman PCH, et al. Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study. Lancet 1993;342:1007–11.

14. Hertog MGL, Kromhout D, Aravanis C, et al. Flavonoid intake and long-term risk of coronary heart disease and cancer in the Seven Countries Study. Arch Intern Med 1995;155:381–6.

15. Knekt P, Jarvinen R, Reunanen A, Maatela J. Flavonoid intake and coronary mortality in Finland: a cohort study. BMJ 1996;312:478–81.

16. Rimm EB, Katan MB, Ascherio A, et al. Relation between intake of flavonoids and risk for coronary heart disease in male health professionals. Ann Intern Med 1996; 125:384–9.

17. Hertog MGL, Sweetnam PM, Fehily AM, et al. Antioxidant flavonols and ischemic heart disease in a Welsh population of men: the Caerphilly Study. Am J Clin Nutr 1997;65:1489–94.

18. Varma SD, Mizuno A, Kinoshita JH. Diabetic cataracts and flavonoids. Science 1977;195:205.

19. Vrijsen R, Everaert L, Boeye A. Antiviral activity of flavones and potentiation by ascorbate. J Gen Virol 1988;69:1749–51.

20. Debiaggi M, Tateo F, Pagani L, et al. Effects of propolis flavonoids on virus infectivity and replication. Microbiologica 1990;13:207–13.

21. Fesen MR, Kohn KW, Leteurtre F, Pommier Y. Inhibitors of human immunodeficiency virus integrase. Proc Natl Acad Sci 1993;90:2399–403.

22. Amoros M, Simoes CM, Girre L, et al. Synergistic effect of flavones and flavonols against herpes simplex virus type 1 in cell culture. Comparison with the antiviral activity of propolis. J Nat Prod 1992;55:1732–40.

23. Spedding G, Ratty A, Middleton E Jr. Inhibition of reverse transcriptases by flavonoids. Antiviral Res 1989;12:99–110.

24. Kaul TN, Middleton E Jr, Ogra PL. Antiviral effect of flavonoids on human viruses. J Med Virol 1985;15:71–9.

25. Mucsi I, Pragai BM. Inhibition of virus multiplication and alteration of cyclic AMP level in cell cultures by flavonoids. Experientia 1985;41:930–1.

26. Ohnishi E, Bannai H. Quercetin potentiates TNF-induced antiviral activity. Antiviral Res 1993;22:327–31.

27. Esanu V, Prahoveanu E, Crisan I, Cioca A. The effect of an aqueous propolis extract, of rutin and of a rutin-quercetin mixture on experimental influenza virus infection in mice. Virologie 1981;32:213–5.

28. Griffith JQ. Clinical application of quercetin: preliminary report. J Am Pharm Assoc 1953;42:68–9.

29. Shanno RL. Rutin: a new drug for the treatment of increased capillary fragility. Am J Med Sci 1946;211:539–43.

30. Bindoli A, Valente M, Cavallini L. Inhibitory action of quercetin on xanthine oxidase and xanthine dehydrogenase activity. Pharmacol Res Commun 1985;17:831–9.

31. Busse W, Kopp D, Middleton E. Flavonoid modulation of human neutrophil function. J Allergy Clin Immunol 1984;73:801–9.

32. Balabolkin II, Gordeeva GF, Fuseva ED, et al. Use of vitamins in allergic illnesses in children. Vopr Med Khim 1992;38:36–40.

33. Gaby A. Preventing complications of diabetes T ownsend Letter 1985;32:307 [editorial].

34. Gaby A. Preventing complications of diabetes Townsend Letter 1985;32:307 [editorial].

35. Schubert W, Cullberg G, Edgar B, Hedner T. Inhibition of 17 beta-estradiol metabolism by grapefruit juice in ovariectomized women. Maturitas 1994;20:155–63.

36. Weber A, Jager R, Borner A, et al. Can grapefruit juice influence ethinylestradiol bioavailability? Contraception 1996;53:41–7.

37. Schubert W, Eriksson U, Edgar B, et al. Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17 beta-estradiol. Eur J Drug Metab Pharmacokinet 1995;3:219–24.

38. Kuiper GG, Lemmen JG, Carlsson B, et al. Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta. Endocrinology 1998;139:4252–63.

39. Miniscalco A, Lundahl J, Regardh CG. Inhibition of dihydropyridine metabolism in rat and human liver microsomes by flavonoids found in grapefruit juice. J Pharmacol Exp Ther 1992;261:1195–9.

40. Hsiu SL, Hou YC, Wang YH, et al. Quercetin significantly decreased cyclosporin oral bioavailability in pigs and rats. Life Sci 2002;72:227–35.

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

42. Ishikawa M, Oikawa T, Hosokawa M, et al. Enhancing effect of quercetin on 3-methylcholanthrene carcinogenesis in C57B1/6 mice. Neoplasma 1985;43:435–41.

43. Hertog MGL, Feskens EJM, Hollman PCH, et al. Dietary flavonoids and cancer risk in the Zutphen elderly study. Nutr Cancer 1994;22:175–84.

44. Castillo MH, Perkins E, Campbell JH, et al. The effects of the bioflavonoid quercetin on squamous cell carcinoma of head and neck origin. Am J Surg 1989;351–5.

45. Stavric B. Quercetin in our diet: from potent mutagen to probably anticarcinogen. Clin Biochem 1994;27:245–8.

46. Barotto NN, López CB, Eyard AR, et al. Quercetin enhances pretumourous lesions in the NMU model of rat pancreatic carcinogenesis. Cancer Lett 1998;129:1–6.

47. Stoewsand GS, Anderson JL, Boyd JN, Hrazdina G. Quercetin: a mutagen, not a carcinogen in Fischer rats. J Toxicol Environ Health 1984;14:105–14.

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