Flavonoids – what are they? Types, sources and properties of flavonoids

Flavonoids are phytochemicals, i.e. substances that occur naturally in plants, with an extremely rich pro-health effect. Their effect on the body is so beneficial that the routine isolated in 1930 as the first of this group was recognized as a newly discovered vitamin – it was called vitamin P. Until now, after years of research and after thousands of other discovered compounds from this group, it happens that this name as the collective term for flavonoids. What are these substances and what are their exact properties? Let’s find out more.

The word “diet” is stereotypically associated with sacrifices, limitations, rigor and a boring, even sterile menu. What a misconception! Nutritionists’ recommendations have long been promoting the composition of a variety of meals, and the more colors on the plate, the better. Vegetables and fruits should form the basis of our nutrition, satisfying all the senses. A meal created in this way pleases the eye, the taste buds, and additionally this blaze of colors is a carrier of substances valuable for health.
Flavonoids – what are these compounds?

Flavonoids are a very diverse group of natural compounds with a polyphenolic structure and of plant origin. They are chemically composed of a 15-carbon skeleton in the C6-C3-C6 system, and its carbon rings can undergo numerous modifications, including hydroxylation or glycosylation, which means that the flavonoids already include over 10,000 compounds, and this number is gradually increasing.

The name of the flavonoids comes from the Latin word flavus, meaning “yellow”. It is them, accumulating in leaves, flowers and fruits (mainly in the outer tissue – the skin), that give them color, and often taste and smell. They protect plants against the harmful effects of ultraviolet radiation, protect against insects and fungi, and also act as hormones and growth regulators.
Types of flavonoids

Due to the diversity of their structural structure, flavonoids are divided into six classes:

• isoflavones (e.g. daidzein, genistein),
• flavonols (e.g. quercetin, kaempferol),
• flavanols (e.g. epicatechin, epigallocatechin, catechin),
• flavones (e.g. apigenin, luteolin, diosmin),
• flavanones (e.g. naringenin, hespereidin),
• anthocyanins (e.g. cyanidin, pelargonidine).

Flavonoids – action and properties. How do they affect the body?

Flavonoids are used in the prevention and therapy of many diseases due to the following properties:

• have a strong antioxidant effect: incl. they scavenge free radicals and chelate iron and copper ions – metals that induce the oxidation process;
• they have anti-cancer properties, and some flavonoids may increase the effectiveness of chemotherapy drugs;
• they have anti-inflammatory and antiallergic activity – e.g. strong quercetin, which not only inhibits the synthesis of inflammatory mediators, but also prevents the release of histamine;
• the similar structure of flavonoids (mainly from the group of isoflavones) to estrogens determines their estrogenic effect, thanks to which they are used in alleviating menopausal symptoms as a safe alternative to hormone replacement therapy;
• reduce the risk of blood clots, have antiatherosclerotic effects, lower blood pressure, strengthen and make the walls of blood vessels more flexible, supporting the treatment of varicose veins and haemorrhoids (e.g. diosmin);
• research shows that some of the flavonoids have anti-diabetic properties, and quercetin protects diabetics against cataracts;
• may be potential components of antiviral therapies: e.g., baicalin and quercetin inhibit HIV replication;
  diuretic and hepatoprotective;
• they delay aging processes and are used in the prevention of neurodegenerative diseases: Alzheimer’s and Parkinson’s diseases; have a calming and anxiolytic effect.

Flavonoids in cosmetics

Flavonoids are used in cosmetics mainly due to their antioxidant effect. They are also valued for the protection of small blood vessels: they strengthen the resistance of their walls to damage. They support the skin’s protective functions, protecting it against the harmful effects of UV radiation. They are found mainly in creams and other preparations for the skin of the face, they have a soothing, moisturizing and anti-aging effect. They soothe ailments of couperose skin. Sealing blood vessels is also of great importance in anti-cellulite preparations.
Flavonoids – where are they? Content in individual products

Flavonoids are natural components of our diet that are available at your fingertips – so what does their average consumption look like? It depends to a large extent on eating habits and fluctuates around 3-70 g per day. Apart from vegetables and fruits, teas (mainly green and black) and red wine are an excellent source of flavonoids.

It should be noted that during thermal processing, many flavonoids are damaged or removed, so it is worth remembering about frequent consumption of raw, unprocessed vegetables.

What are the main sources of flavonoids in the human diet? Below, in some food products, the content of flavonoid compounds is given:

• isoflavones: soybeans (1 mg / g grain), soy products, legumes;
• flavonols: onion (0.3 mg / g), apples (0.03 mg / g), tea (10–25 mg / l), lettuce, broccoli, dark grapes, elderberries, cabbage;
• flavanols: tea (1 mg / ml), dark, dark chocolate (> 70% cocoa – 0.8 mg / g), red wine (270 mg / l), apples, kiwi (4.5 mg / kg);
• flavones: celery, red pepper, parsley, lemon, thyme;
• flavanones: oranges, grapefruits (125-250 mg / l juice);
• anthocyanins: grapes, red wine (26 mg / l), cherries (4.5 mg / kg), strawberries (0.15 mg / kg), black currants, elderberries, chokeberry, bilberry.

Flavonoids in preparations

A popular alternative or addition to flavonoids taken with food are the increasing number of dietary supplements containing high doses of these compounds. In pharmacies, there are preparations in the form of tablets, capsules and syrups, mainly intended for adults, some also for children.

Single- or multi-component drugs and supplements with quercetin (as popular allergy preparations), rutin (often with vitamin C as an immune enhancing product), diosmin and hesperedyin in the treatment of blood vessel diseases are widely known and used. Isoflavones are found in preparations that alleviate menopausal symptoms, silymarin has a protective effect and strengthens the liver. Flavonoids are a component of ginkgo leaf extracts, which can be found in preparations that improve memory and cognitive functions.
Before using a medication or a dietary supplement, always read the product leaflet and consult your doctor or pharmacist if you have any doubts.

Flavonoids – contraindications, side effects

Flavonoids consumed along with the diet are now considered to be completely safe. Oral preparations with flavonoids are also well tolerated – however, concerns are raised by the possibility of taking too high a total dose of these compounds from both of the above sources. Excessive doses of flavonoids can possibly reduce the bioavailability of certain elements, folic acid and vitamins, and block or reduce the absorption of antibiotics. It is recommended to keep an interval of about four hours between the taken antibiotic and the flavonoid preparation.
Flavonoids can adversely affect the functioning of the thyroid gland.

What is most often noted during increased supplementation is the risk that under certain conditions and high concentrations, flavonoids may have a pro-oxidative effect, i.e. increase the oxidation of molecules.