Quercetin

A substance belonging to the flavonoids, which are secondary plant substances and are responsible for the colouring of flowers, leaves and fruits. Catechins (tanning agents) and anthocyanins (flower dyes) also belong to the large group of flavonoids.

Flavonoids have a uniform chemical structure with a phenylchroman skeleton. This consists of three rings with attached hydroxyl groups. A large variety of flavonoids is created by numerous other substitutions.

In plants, flavonoids mostly occur as glycosides. They are attached to the middle ring C with a sugar molecule (rhamnose, glucose, galactose). As glycosidically connected with rhamnose, quercentine is found in the bark of the American dye ranges (Quercus tinctoria) (quercitrin). It was used to dye wool, silk or cotton.

Quercetin has numerous biological effects: it has antioxidant, antiviral and anti-inflammatory properties and protects the cardiovascular system. Furthermore, tumor-protective (antiproliferative) and antiviral effects are described. The anti-inflammatory effect of quercetin is based on its antioxidant properties and the inhibition of inflammatory enzymes(cyclooxygenase, lipoxygenase): quercetin inhibits the release of inflammatory mediators such as leukotrienes and prostaglandins. Inhibition of histamine liberation from mast cells and basophilic granulocytes also has an anti-inflammatory effect.

Anti-allergic: Due to the stabilizing effect of quercetin on mast cells, the substance could have an anti-allergic effect analogous to the effect of the synthetic flavonoid analogue cromolyn sodium(cromoglycic acid).

Prevention of cardiovascular diseases: The most important cardiovascular effects of quercetin are its antioxidant and anti-inflammatory effects. Quercetin has also been shown experimentally to inhibit platelet aggregation.

Anti-inflammatory: Quercetin is indicated in all inflammatory diseases as it inhibits the formation of prostaglandins and leukotrienes and the release of histamine, as leukotriene B4 is a powerful bronchoconstrictor. The inhibitory effect of quercetin on xanthine oxidase reduces uric acid formation and can be used to treat gout.

400-500 mg three times/day p.o. The water-soluble quercetin preparation Quercetinchalkon is better absorbed. Dosage 250 mg three times/day p.o.

In pure form, the aglycone quercetin is poorly absorbed.

1. D'Andrea G (2015) Quercetin: A flavonol with multifaceted therapeutic applications? Fitoterapia 106:256-271.
2. Gormaz JG et al,(2015) Cardiovascular Disease: A Target for the Pharmacological Effects of Quercetin. Curr Top Med Chem 15:1735-1742.
3. Larson AJ et al(2012) Therapeutic potential of quercetin to decrease blood pressure: review of efficacy and mechanisms. Adv Nutr 3:39-46.
4. Li Y et al (2016) Quercetin, Inflammation and Immunity. Nutrients 8:167.
5. Yang F et al (2015) Quercetin in prostate cancer: Chemotherapeutic and chemopreventive effects, mechanisms and clinical application potential (Review). Oncol Rep 33:2659-2668.