Vitamin supplements guide   Vitamins & health supplements guide

Quercetin quick review
Description: also called meletin, a type of phytoestrogen, occurring as a glycoside in the rind and bark of numerous plants.
Health benefits: has potent antioxidant and anti-inflammatory activity, prevents damage to blood vessels, blocks an enzyme that leads to accumulation of sorbitol.

Sources & dosage: onions, apples, green and black tea. Recommended adult dosage for general supplementation is about 200 to 400 mg three times daily.
Activated Quercetin Tablets
Activated Quercetin is a unique bioflavonoid derived from plant sources. In human cell culture studies, quercetin has been shown to inhibit histamine release. Additional research needs to be conducted to confirm the effects of quercetin, if any, in humans. Bromelain is a pineapple enzyme that may assist the body in times of stress. Magnesium ascorbate is a buffered (non-acidic) form of vitamin C that helps support the immune system. Click here for more information.


Quercetin is a yellow powdered crystalline compound produced synthetically or occurring as a glycoside in the rind and bark of numerous plants, used medicinally to treat abnormal capillary fragility. Also called meletin. Quercetin is classed as a type of 'phytoestrogen', which are oestrogen-like chemicals that occur in some plants. Quercetin also works as an antioxidant by scavenging damaging particles in the body known as free radicals. Flavonoids are the agents responsible for the pigment in foods derived from plants. The primary sources of quercetin are red grape juice, grapefruit, onions, black tea, and apples. Lesser amounts are found in other fruits and vegetables.

Quercetin health benefits

Quercetin is a naturally occurring flavonoid compound found in most plant tissues. It is being studied for apparent benefical effects
including cardiovascular protection, anti-cancer activity, anti-ulcer effects, anti-allergy activity, cataract prevention, antiviral activity, and anti-inflammatory effects. In the body, quercetin has potent antioxidant and anti-inflammatory activity, where it can protect cellular structures and blood vessels from the damaging effects of free radicals. As an antioxidant, it protects LDL cholesterol ("bad" cholesterol) from becoming damaged. Quercetin prevents damage to blood vessels by certain forms of cholesterol and other chemicals produced by the body. Quercetin blocks an enzyme that leads to accumulation of sorbitol, which has been linked to nerve, eye, and kidney damage in those with diabetes.

Quercetin may inhibit the overproduction of both nitric oxide and protein-tyrosine kinase. Quercetin inhibits the production and release of histamine and other allergic/inflammatory substances. Histamines are responsible for allergic and inflammatory reactions. The body may use quercetin to strengthen the mast cells, involved in the release of histamine, potentially inhibiting that activity. Free radicals are thought to contribute to the development of certain eye disorders including cataracts and macular degeneration. Flavonoids, such as quercetin, neutralize free radicals and may play a role in the prevention and/or treatment of these eye conditions. Quercetin and other flavonoids from fruits and vegetables have long been considered important substances to possibly help prevent cancer.


Dietary sources of quercetin

Quercetin can be found in onions, apples, green and black tea and in smaller amounts in leafy green vegetables and beans. Quercetin is typically found in plants as glycone or carbohydrate conjugates. Olive oil, grapes, dark cherries, and dark berries, such as blueberries, blackberries, and bilberries are also high in flavonoids including quercetin.


Dosage, intake, recommended daily allowance (RDA)

There is no fixed dietary recommendation for quercetin intake. Recommended adult dosage for general supplementation is about 200 to 400 mg three times daily. For patients with chronic prostatitis, 500 mg twice daily was shown to be effective in reducing symptoms. To relieve allergy symptoms, take 250 to 600 mg per day divided in several doses. Quercetin supplements are available in several strengths in powder or capsule form. They are often packaged with bromelain (an enzyme found in pineapple) as an anti-inflammatory agent. If used with bromelain, the amount of bromelain should be equal to the amount of quercetin.