Quercetin and Naringin Flashcards
Quercetin
Quercetin is the most abundant of the flavonoids. It is also a building block for other flavonoids (e.g. kaempferol):
* Quercetin has a fast excretion rate so needs to be consumed regularly for therapeutic use.
* Therapeutic dosage range: 150‒1500 mg / day.
Quercetin: Food sources
Onions (especially red),
apples (especially the peel), grapes, capers, asparagus, tomatoes, kale, brassica vegetables and
berries ( blueberries, bilberries, blackberries,
elderberry, cranberry and goji.)
Quercetin: Functions
Cardiovascular health
Anti-cancer
Immune system
Zanthine oxidase
Quercetin: Cardiovascular health
- Quercetin is a powerful antioxidant protecting the vascular endothelium. It inhibits LDL oxidation.
- Shown to have vasodilatory effects (via nitric oxide release), reduces platelet aggregation and lowers blood pressure (in those hypertensive) via ACE inhibiting properties.
- Supports athletic performance (endurance) by ↑ blood circulation.
- Dosage: 150 mg‒1000 mg per day.
Quercetin: Cardiovascular health - Therapeutic uses
- Cardiovascular diseases (e.g. coronary artery disease) incl. prevention.
- Hypertension.
- Hyperlipidaemia.
- Previous myocardial
infarction. - Exercise performance.
Quercetin: Anti-cancer - Therapeutic uses
- Its anti tumour functions occur by a variety of mechanisms:
‒ Shown to induce cell cycle arrest (e.g. in leukaemic, prostate and ovarian cancer cells) induces apoptosis.
‒ It can inhibit blood vessel growth. In prostate and breast cancers, quercetin targets the VEGFR 2 mediated angiogenesis pathway.
‒ Evidence of anti- metastatic properties. - Shown to reduce head / neck skin damage during radiotherapy.
- Shown to increase the efficacy of some types of chemotherapy including: Cisplatin, busulfan, topotecan, cyclophosphamide, gemcitabine
Quercetin: Immune System
- Anti inflammatory quercetin inhibits LOX and COX, and is also a potent
down regulator of NF-κB . - Anti-histamine - quercetin inhibits histamine release by mast cells.
- Reduces inflammation in the brain (and is hence protective against
Alzheimer’s and Parkinson’s , of which
inflammation is an exacerbating factor).
Quercetin: Immune System - Therapeutic uses
- Hay fever.
- Histamine reactions e.g. urticaria, hives.
- Asthma.
- Prostatitis.
- IBD
- Arthritis (e.g. RA, osteoarthritis).
Quercetin: Xanthine oxidase
- Quercetin can inhibit xanthine oxidase (normally converts purines -> uric acid
Therapeutic uses
* Gout.
Quercetin: Absorption
Absorption: Only a small percentage of ingested quercetin is absorbed in the blood:
‒ Quercetin occurs in most food as a glycone so it has to split from the sugar portion to be absorbed and become active.
‒ Onion and shallots contain quercetin in its unbound (aglycone) form, which may make absorption easier
‒ Quercetin is hydrophobic, so is best absorbed with fats, emulsifiers or apple pectin.
Quercetin: Safety
No side effects noted in doses of a few grams a day.
Quercetin: Interactions
Some antibiotics e.g. fluoroquinolones and some types of chemotherapy e.g. paclitaxel.
Naringin
Naringin belongs to the group of flavanones. It is metabolised to naringenin in the gut by intestinal bacteria
Naringin: Food sources
Citrus fruits (especially in grapefruit, where naringin is responsible for the fruit’s bitter taste). Also found in cooked tomato paste
Naringin: Caution
Grapefruit is contraindicated with numerous medications because naringenin inhibits intestinal CYP3A4 (the pathway used for many pharmaceutical drugs). Its inhibition results
in less metabolism and thus higher circulating levels of drugs.
