Quercetin

Overview

Quercetin is one of a number of water-soluble plant pigments called bioflavonoids. Quercetin and the other bioflavonoids cannot be synthesized by humans. However, they reportedly exert a wide variety of biological effects when ingested.

Dosage Info

Dosage Range

200-400mg, 2 to 3 times daily.

Most Common Dosage

400mg daily.

Dosage Forms

Tablets and capsules.

Adult RDI

None established

Adult ODA

None established

RDA

Active Forms

Quercetin.

Absorption

Studies in animals and humans indicate that orally ingested quercetin is not very well absorbed.

Toxicities & Precautions

General

There are no known toxicities associated with quercetin.

Functions in the Body

Vasorelaxation

Quercetin exhibits coronary vasorelaxation properties. (1) In an animal model, administration of quercetin resulted in a lowering of elevated blood pressure. (2)

Anti-inflammatory and Antihistamine Effects

Inhibits a number of substances that are responsible for producing symptoms of allergy and inflammation. (3) Part of quercetin’s anti-inflammatory activity is due to its ability to inhibit the production of the pro-inflammatory cytokine called tumor necrosis factor-alpha (TNF-alpha). (4)

Capillary Strength and Permeability

One of the bioflavonoids that helps increase the strength of the capillaries and to regulate their permeability. (5)

Antioxidant

Quercetin is an antioxidant that specifically prevents the oxidation of LDL cholesterol. (6)

Antiviral Activity

Quercetin may exert antiviral activity against several types of viruses including herpes simplex virus type 1, polio virus type 1, reverse transcriptase of HIV and other retroviruses. (7)

Anticancer effects

Quercetin reportedly exerts anticancer effects via complex effects on signal transduction, which influence cell proliferation and angiogenesis. (8) , (9) , (10)

Clinical Applications

Inflammatory Conditions

Quercetin has inhibitory effects on inflammation-producing enzymes such as cyclooxygenase and lipoxygenase. (11) This decreases the production of inflammatory mediators, including leukotrienes and prostaglandins. It also inhibits the release of histamine from mast cells and basophils, which provides additional anti-inflammatory activity. (12)

Atherosclerosis.

Quercetin’s antioxidant properties help prevent LDL cholesterol from becoming oxidized as well as protecting against the cytotoxic properties of LDL cholesterol that has already been oxidized. (13)

Cataracts

The antioxidant activity of quercetin helps protect the eyes from the type of free radical damage that leads to the development of cataracts. (14) Quercetin is also a strong inhibitor of aldose reductase, which is the enzyme that catalyzes the conversion of glucose to sorbitol in the lens of the eye and plays a part in the formation of diabetic cataracts. (15)

Allergies

Quercetin’s ability to stabilize mast-cells makes it beneficial for use in preventing histamine release in allergy cases. Since absorption of quercetin is poor, much of its anti-allergy effects may be due to anti-inflammatory and antihistaminic effects in the gut. (16)

Symptoms and Causes of Deficiency

Since quercetin is not an essential nutrient for humans, there is no deficiency condition associated with it. Bioflavonoid deficiency may result in poor vascular integrity including varicosities, bruising, and bleeding easily.

Dietary Sources

Quercetin is found in many foods including apples, onions, tea, berries, grapes, and brassica vegetables, as well as many seeds and nuts.

References

  1. View Abstract: Rendig SV, Symons JD. Effects of red wine, alcohol, and quercetin on coronary resistance and conductance arteries. J Cardiovasc Pharmacol. Aug2001;38(2):219-27.
  2. View Abstract: Duarte J, Galisteo M, Ocete MA, et al. Effects of chronic quercetin treatment on hepatic oxidative status of spontaneously hypertensive rats. Mol Cell Biochem. May2001;221(1-2):155-60.
  3. View Abstract: Formica JV, Regelson W. Review of the biology of Quercetin and related bioflavonoids. Food Chem Toxicol. Dec1995;33(12):1061-80.
  4. View Abstract: Wadsworth TL, McDonald TL, Koop DR. Effects of Ginkgo biloba extract (EGb 761) and quercetin on lipopolysaccharide-induced signaling pathways involved in the release of tumor necrosis factor-alpha. Biochem Pharmacol. Oct2001;62(7):963-74.
  5. Hertog MG, Hollman PC. Potential health effects of the dietary flavonol quercetin. Eur J Clin Nutr. Feb1996;50(2):63-71.
  6. View Abstract: O’Reilly JD, Sanders TA, Wiseman H. Flavonoids protect against oxidative damage to LDL in vitro: use in selection of a flavonoid rich diet and relevance to LDL oxidation resistance ex vivo? Free Radic Res. Oct2000;33(4):419-26.
  7. View Abstract: Kaul TN, Middleton E Jr, Ogra PL. Antiviral effect of flavonoids on human viruses. J Med Virol. Jan1985;15(1):71-9.
  8. View Abstract: Morrow DM, Fitzsimmons PE, Chopra M, McGlynn H. Dietary supplementation with the anti-tumour promoter quercetin: its effects on matrix metalloproteinase gene regulation. Mutat Res. Sep2001;480-481:269-76.
  9. View Abstract: Mori H, Niwa K, Zheng Q, et al. Cell proliferation in cancer prevention; effects of preventive agents on estrogen-related endometrial carcinogenesis model and on an in vitro model in human colorectal cells. Mutat Res. Sep2001;480-481:201-7.
  10. View Abstract: Van Erk MJ, Roepman P, Van Der Lende TR, et al. Integrated assessment by multiple gene expression analysis of quercetin bioactivity on anticancer-related mechanisms in colon cancer cells in vitro. Eur J Nutr. Apr2004;:1-14.
  11. View Abstract: Loggia Della, et al. Anti-inflammatory Activity of Benzopyrones that are Inhibitors of Cyclo- and Lipo-oxygenase. Pharmacol Res Commun. 1988;20:S91-S94.
  12. View Abstract: Bronner C, Landry Y. Kinetics of the Inhibitory Effect of Flavonoids on Histamine Secretion from Mast Cells. Agents Actions. 1985;16:147-51.
  13. View Abstract: Negre-Salvayre A, et al. Quercetin Prevents the Cytotoxicity of Oxidized LDL on Lymphoid Cell Lines. Free Radic Biol Med. 1992;12(2):101-06.
  14. Beyer-Mears A, et al. Diminished Sugar Cataractogenesis by Quercetin. Exp Eye Res. Jun1979;28(6): 709-16.
  15. View Abstract: Chaudry PS, et al. Inhibition of Human Lens Aldose Reductase by Flavonoids, Sulindac, and Indomethacin. Biochem Pharmacol. 1983;32:1995-98.
  16. View Abstract: Bronner C, Landry Y. Kinetics of the Inhibitory Effect of Flavonoids on Histamine Secretion from Mast Cells. Agents Actions. 1985;16:147-51.