Quercetin

Quercetin belongs to the class of water-soluble plant pigments (colorants) within the phytamines. It is a flavonol and belongs to the group of flavonoids, which are classified as polyphenols. With the help of quercetin as a building block, other flavonoids can be built up. Quercetin is a phytoestrogen, i.e. a plant hormone, and is considered to be the best-studied flavonoid to date. Many studies have shown a wealth of effects of this phytamine on humans.

Quercetin - many functions in the human body

Quercetin acts like an antihistamine and has anti-allergic and anti-inflammatory effects. As it can reduce inflammation in the airways and lungs and block allergic reactions to pollen, it helps to alleviate hay fever, sinusitis and asthma. Quercetin has an antithrombotic effect, it can inhibit the aggregation of blood platelets and thus prevent the formation of thromboses. Quercetin is an effective antioxidant; it protects the LDL fraction of blood lipids, the so-called "bad" cholesterol, from oxidation. As an antioxidant, it can also promote eye health. Quercetin has a relaxing effect on smooth muscle cells, which helps to prevent high blood pressure and arrhythmia. Quercetin also blocks an enzyme that leads to the accumulation of sorbitol, a type of sugar. Elevated levels of sorbitol can contribute to secondary damage in diabetes. Whether quercetin can also be used to prevent such damage still needs to be investigated in more detail. Some phytoestrogens have anti-estrogenic effects that can reduce the risk of some types of cancer. Anti-oestrogenic activity has been confirmed for quercetin in experimental studies. For example, it has been shown that quercetin can inhibit the growth of prostate cancer cells.

Quercetin - in many types of fruit and vegetables

Quercetin is a good reason to remember the well-known English rule: "An apple a day keeps the doctor away". Loosely translated, this means that an apple a day can keep you healthy. Well, it should be a little more in terms of different types of fruit and vegetables. Nutritionists and doctors recommend five portions of fruit and vegetables a day. Onions and chives should not be forgotten as they contain the most quercetin. Cranberries and blackcurrants also contain a lot of it, but as they are not eaten very often, apples are a good source of quercetin. Green and black tea also provide quercetin. Smaller amounts are also found in green leafy vegetables and beans.

Quercetin content in mg per 1 kg

• Onions 284-486 mg
• Chives 245 mg
• Cranberries 156 mg
• Blackcurrants 69 mg
• Kale 60 mg
• Blackberries 45 mg
• Apples 21-72 mg

Quercetin - the health effects

Due to its many functions in the body,quercetin can contribute to the prevention of some diseases:

• to prevent and alleviate allergies (including hay fever)
• to prevent atherosclerosis
• to lower high cholesterol
• to prevent some types of cancer (stomach, lung, pancreatic and breast cancer)
• to prevent eye diseases (cataracts, retinopathy)

Quercetin - safe to take

Quercetin is considered safe to take and no side effects have been reported to date. However, overdoses should be avoided and use during pregnancy is not recommended.

Quercetin - the daily intake

It is not known exactly how much quercetin we take in with our food every day. It is estimated that around 200 to 500 mg of quercetin are ingested per day. A limit value for quercetin deficiency has not been set.

Quercetin - for prevention and therapy

Quercetin can be used as a preventative measure if there is a risk of the diseases mentioned above. The dosage is usually between 500 and 1500 mg daily and should be determined by the therapist. When taking medication at the same time, attention should be paid to possible interactions. Flavonoids protect and promote the absorption of vitamin C, which is why they are often recommended in combination.

Safety and side effects

Quercetin is potentially safe and harmless for most people when taken orally for short periods of time. Quercetin has been used safely in amounts up to 500 mg twice daily for 12 weeks. It is not known whether long-term use or use of larger amounts is safe and harmless.

Quercetin can cause headaches and a tingling sensation in the arms and legs. Very high doses could cause kidney damage.

When quercetin is administered intravenously in reasonable amounts (less than 722 mg), it may be safe and harmless. Larger amounts administered intravenously may not be safe and harmless. There are reports of kidney damage when larger amounts are administered intravenously.

Precautions and warnings

Pregnancy and lactation: Not enough is known about the safety of quercetin during pregnancy and lactation. For this reason, pregnant and breastfeeding women should avoid quercetin to be on the safe side.

Interactions with medications

Quercetin should be taken with caution in combination with the following medications:

Antibiotics (quinolone antibiotics)

Taking quercetin in combination with some antibiotics could reduce the effectiveness of some antibiotics. Some scientists believe that quercetin may prevent some antibiotics from killing bacteria. However, it is too early to say whether this is a major cause for concern.

Cyclosporine

Cyclosporine is processed and broken down by the liver. Quercetin could reduce the rate at which the liver breaks down cyclosporine. Taking quercetin in combination with cyclosporine could increase the effects and side effects of cyclosporine. For this reason, you should talk to your doctor before using quercetin if you are taking cyclosporine. Drugs that are broken down by the liver (cytochrome P450 2C8 (CYP2C8), cytochrome P450 2D6 (CYP2D6), cytochrome P450 3A4 (CYP3A4) and cytochrome P450 2C9 (CYP2C9) substrates)

Some drugs are broken down by the liver. Quercetin may reduce the rate at which the liver breaks down certain drugs. Taking quercetin in combination with drugs that are broken down by the liver may increase the effects and side effects of some drugs. For this reason, you should consult your doctor before taking quercetin if you are taking medicines that are broken down by the liver.

Drugs that are transported into the cells by pumps (P-glycoprotein substrates)

Some drugs are transported into the cells by pumps. Quercetin can make these pumps less active and increase the amount of drug absorbed by the body. This can increase the side effects of certain drugs.