What are Flavonoids?

Flavonoids (or biflavonoids) are 15 Carbon containing polyphenolic water soluble compounds belonging to Polyphenol family. They are a type of Plant Secondary metabolites. Its name is derived from the Latin word flavus meaning yellow, their colour in nature. They were earlier referred to as Vitamin P due to their effect on permeability of vascular capillaries. Flavonoids are found in almost all parts of the plants.

Flavonoids occur both in a free state and as Glycosides (referred as Flavonol Glycosides) and are the largest group of naturally occurring phenols. Among 2,000 known flavonoid compounds, 500 of them occur in a free state. Their structures consist of three acetate units and a Phenylpropane unit and are regarded as C6-C3-C6 compounds i.e fifteen Carbon skeleton where two C6 moieties which are benzene ring are joined together by a three carbon link which thereby is formed into gama-pyrone ring. The variation in the state of oxidation of the C3 moieties determines the properties and class of these compounds.

The flavonoids which occur as Glycosides (O-glycosides and C-glycosides) contain one or more of the phenolic hydroxyl groups which are combined with sugar residues (simple hexoses and pentoses and di and trisaccharides and acetylated sugars).

Flavonoids consist of the following major subgroups

  • Flavone-Quercetin, Fisetin, luteolin, and apigenin.
  • Isoflavone-Genistein and diadzein.
  • Flavanone- rutin, Hesperidin and Naringin.
  • Flavonol-Kaempferol and myrcetin.
  • Flavanonol-Taxifolin (dihydroquercetin), dihydrokaempferol.
  • Flavanols/Flavan-3-ol-Catechin, gallocatechin, Epicatechin, Epigallocatechin.
  • Anthocyanins- These are the sugar-free pigments which are responsible for the numerous shades of blue, purple and violet and mostly all shades of red which appear in the cell sap of flowers, fruits, leaves and stems present in the dissolved state designed to attract pollinator animals. Examples are pelargonidin, cyanidin and delphinidin.
  • Chalcone- unstable isomers of flavonones
  • Aurones- Bractetin and sulfuretin.

How are Flavonoids useful to our body?

Anti-oxidant activity:- Both highly hydroxylated flavonols and flavanols and flavone, Quercetin are most commonly known for their anti-oxidant activity against low density lipoprotein thereby preventing the risk of development of atherosclerosis because of their appropriate structural features for free radical scavenging activity.

Cardiac Stimulants: Quercetin, a flavone shows positive ionotropic action of cardiac activity of the heart. It reduces the risk of development of Coronary Heart diseases.

They are used to decrease capillary fragilities and show Vitamin P action (effect on permeability of vascular capillaries):- Flavanones Rutin and Hesperidin strengthen weak capillary blood vessels by increasing the tensile strength and by reducing permeability of capillary walls. The former flavanone has also been used to treat the diseased state showing symptoms of capillary bleeding (therefore also used as anti-hemorrhage and anti-sclerotic agent) associated with increased capillary fragility.Flavonoids

Enhance the activity of Vitamin C:  Both rutin and hesperadin have the tendency to increase the intracellular levels of Vitamin C.

Anti-asthmatic – Experimental studies have shown that alcohol extract of red variety of edible onion, Allium cepa gives effective relief in asthma. Later Quercetin, a flavone was isolated from it which was responsible for the activity in experimental animals and asthma patients.

Anti-inflammatory and anti-allergic action:  Quercetin is majorly responsible for the prevention of excessive inflammation of the body. In the case of an infusion of matricaria flowers (Chamomilla recutita, German chamoqrile), used for its anti-inflammatory action in the treatment of acute gastritis, it has been shown by the mouse-ear test that it is the flavonoids and not the volatile oils that are responsible for activity.

Anti-hyperglycemic/Anti-diabetic agent: – Epicatechin present in the bark of tree Pterocarpus marsupium have been shown to have anti-diabetic activity.

Anti-microbial: Isoflavone types of flavonoids have been reported to possess insecticidal and antifungal properties.

Anti-cancer:  They induce mechanisms that inhibit tumor invasion and affect the carcinogens. Genistein (an isoflavone) is one among them. Others such as Catechins (Strawberries and tea), Kaempferol (apples and sprouts) and Quercetins have found to decrease the risk of lung cancer.

Oestrogenic: – Isoflavones also produce oestrogenic action in the body.
Anti-HIV activity: – Glycyrrihzoflavone, lsolicoflavonol and Licocholcone present in Glycirrhizha glabra produce similar action to liquorice coumarins and exhibit anti-HIV activity.

Identification of Solanaceae species: – Due to the presence of Kaempferol in Senna leaves; it is now possible to identify the Solanaceae species.

Rich Sources of Flavonoids

Citrus fruits like lemon, orange and others contain a high amount of Hesperidin, a flavanone. Both green and black teas contain Polyphenols, about 25% flavonoids. Other good sources of Flavonoids are berries (raspberries, blueberries), onions (particularly red), pulses, black beans (dry beans), grapes, parsley, cabbage, soy beans, soy products, legumes, red wine and dark chocolate (cocoa content should be 70% or greater as it contains high amounts of epicatechin, a flavanol).

Issues associated along with Flavonoids

  • Carcinogen potential: – As flavonoids is found to be strong topoisomerase inhibitors thereby exhibiting carcinogic effects.
  • DNA mutations: – High flavonoid containing diet in mothers’ suggested an increase in MLL genes thereby inducing DNA mutations and acute myeloid leukemia in neonates. If you are administering intravenously quercetin at doses 1000 mg or more it might cause renal (kidney) toxicity in that trial.
  • Nausea, Headache, or tingling or extremities might be felt if you are taking Quercetin supplements.
  • Reports of hepatotoxicity (liver toxicity) after consumption of supplements containing tea (Camellia sinensis) extracts have been found.

Heat, degree of acidity (pH), and degree of processing can have a dramatic impact on the flavonoid content of food. Overcooking excess heating, frying or boiling) of vegetables can deteriorate the flavonoid content of the food thereby changing the level of nutrients. Therefore care should be taken and overcooking should be prevented. They are readily available in almost all plants, vegetables and fruits and provide numerous pharmacological and medicinal beneficial effects. Nowadays, they are also readily available as dietary supplements.

The daily flavonoid intake in the human diet can be highly variable, with estimations ranging from 25 mg to more than 500 mg.