Active Ingredients

Quercetin – Effect, Application & Risks


Quercetin is a yellow pigment naturally occurring in many plants. The effect of quercetin is that of a radical scavenger. How exactly this effect comes about has not yet been scientifically proven.

What is quercetin?

Quercetin belongs to the subgroup of flavonols and to the group of flavonoids and polyphenols. It is a yellow pigment found in plants. Quercetin is found in many foods and is mostly found in the peels. For this reason, large amounts of quercetin are lost when peeling many types of fruit and vegetables. The processing of food in the kitchen can also partially destroy quercetin.

Fruits and vegetables with a particularly high quercetin content include lovage , onions , tea, apples , blueberries , blackcurrants , raspberries , blackberries , cherries, chives , mountain ash , sea buckthorn , organic tomatoes , kale , red grapes or capers . Because quercetin is found in grapes, it persists in wine.

Quercetin is also offered in concentrated form as a drug to treat various diseases.

Pharmacological action

The exact mode of action of quercetin is still the subject of research and is being intensively examined in scientific studies. In general, it has been proven that quercetin inhibits oxidation processes in vivo. However, it has not yet been possible to definitively clarify how this actually works.

It has been generally proven, among other things, that quercetin is a natural opponent of histamine . Quercetin also has a fundamental anti-inflammatory effect in the body. Thanks to this property, it has also been proven to protect against neurodegenerative diseases. In addition, quercetin also promotes blood circulation and lowers blood pressure, even if it has not yet been possible to clarify why this is the case.

A lot of quercetin can increase the number of mitochondria in muscle cells. Quercetin also prevents dioxins from causing damage in various places in the body. This also has to do with its antioxidant properties. Together with vitamins A , C and E and other bioflavonoids (e.g. catechins), quercetin is even more effective, as these natural substances complement each other in their effect.

Medical Application & Use

One of the most important properties of quercetin is that it has been shown to be helpful in the treatment of cancer , although what exactly happens in the body has not yet been fully clarified.

Quercetin has been shown to inhibit inflammation of all types. In this way, it has been shown to be helpful in the treatment of many allergic conditions . It protects against hay fever , asthma and other respiratory diseases , allergic skin reactions and other reactions of this type.

It has also been shown to protect against inflammatory diseases of the prostate . It has also been shown that quercetin has a preventive effect on neurodegenerative diseases such as Alzheimer’s or Parkinson’s . In this case, too, it is assumed that this is related to the property of quercetin to have an anti-inflammatory effect. However, the exact mode of action is still being investigated in the case of these diseases.

Regarding the beneficial effect of quercetin in the treatment of cataracts , it is believed that in this case quercetin inhibits the conversion of glucose to sorbitol by inhibiting the enzyme aldose reductase. Quercetin also has a general inhibitory effect on various viruses in the body .

The fact that quercetin has been shown to promote blood circulation and lower blood pressure is attributed, among other things, to the inhibition of platelet aggregation . Quercetin may also protect the testicles from the damage caused by dioxins and, due to its property of promoting the formation of more mitochondria in muscle cells, may help increase athletic performance.

Risks & side effects

The dosage determines whether quercetin can cause side effects and damage to health. In its natural form in food, quercetin is very healthy and cannot cause any harm. As a chemically manufactured product, however, it is toxic in very high concentrations. Therefore, it is important to follow the dosing instructions carefully when administering quercetin as a drug to treat a condition or as a preventive measure.

From just a mild to severe headache or a tingling in the arms and legs, to damage to the kidneys , overdoses can also cause side effects. High doses of quercetin can also cause mutations in the germ cells .

Since quercetin in turn not only prevents tumor cells from growing, but can even kill them, the treating physicians have to weigh up carefully whether quercetin should nevertheless be used as a drug with possible side effects.

In relation to other drugs, quercetin slows down the metabolism of cyclosporine and also inhibits the action of some antibiotics .

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.