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Flavonoids are organic chemical substances included in plants, included in the composition of polyphenols. About 4000 compounds are known, which occurs as well as in leafs, seeds, flowers and fruit plants. They perform many functions as color giving, act as antioxidants, regulate growth or hormones and protect plants against fungi and insects.

Most of flavonoid compounds are included in bitter chocolate, in which cacao provides over 70% of all ingredients. However main source of flavonoids in diet are vegetables and fruits. Vegetables that consist of large number of flavonoids are for example: onion, paprika, broccoli and tomatoes. In turn, among the fruits rich in these compounds, predominates: citrus fruits, grapes, apples and blueberries. Furthermore, rich sources of flavonoids are also seeds of legumes, spices, coffee, tea and red wine.

Due to their construction we distinguish several classes of flavonoid compounds:

  • flavonones (oranges, grapefruits)
  • flavanols (chocolate, apples, tea, wine),
  • flavones (pepper, red pepper, thyme, celery, lemon)
  • isoflavones (soy, beans, peas)
  • flavonols (onion, broccoli, apples, tea),
  • anthocyanidins (cherries, strawberries, chokeberry, currants, wine).

The average daily intake of flavonoids is about 1 g and is dependent on geographical location. In western countries an average of 800 mg flavonoids/day is provided to the body, in turn eastern societies consumes up to 2 g/day. However, it should be noted that the content of flavonoids in the human body depends on the intake amount of compounds, their class and absorption process.

The main place of absorption of flavonoids in the human body is the intestine and the liver, where they metabolize. Flavonoids delivered to the human body, are not stored in it. Part of the metabolites of flavonoids is supplied with blood to the tissues, whilst others undergo reabsorption, and the remainder is removed from the body by the kidneys. The bioavailability of flavonoids depends on the class, its physico-chemical properties and construction (the presence or absence of functional groups). It must be also added that better absorption is recorded in men than in women.

Due to the large diversity in the construction of the flavonoid compounds, they possess a broad spectrum of activity in the human body.

  • Antioxidant action of flavonoids is mainly based on the capture and removal of already generated free radicals and reactive oxygen forms and reducing their formation by inhibiting the relevant enzymes. Flavonoid compounds are also indirectly responsible for protection of low molecular weight antioxidants.
  • By preventing the formation and removing from blood already formed reactive oxygen forms, flavonoids protect the cholesterol from oxidation process. In addition, through its reabsorption, contribute to a reduction of its concentration in the human body. They are also responsible for the inhibition of LDL oxidation and increasing HDL cholesterol fraction content, as well as reducing the amount of triglycerides.
  • By increasing cell resistance against LDL cholesterol harmful action and decreasing the amount of triglycerides.
  • Some flavonoid compounds (vitamin P) are also responsible for the sealing and the relaxation of blood vessels. In addition, by inhibiting the enzyme hyaluronidase, or lysyl oxidase, flavonoids reduce brittleness and destruction of blood vessels.
  • Epicatechin shows anti-diabetic activity. It stimulates the formation of insulin, which impairment of production and secretion is a major cause of diabetes. In turn, quercetin prevents creating of cataracts in diabetic patients.
  • Some flavonoids can also reduce blood pressure and prevent blood clots.
  • Quercetin, vitamin P, apigenin or myricetin shows antiallergic activity.
  • As a result of the similarities in the construction of isoflavones to estrogens, they can be used in delaying and relieving the symptoms of menopause.
  • Flavonoids also affects on the immune system, primarily by inhibiting the proliferative process of lymphocytes, the synthesis of IgG antibody classes: A, E, G, and M and the secretion of cytokines.
  • Anti-inflammatory activity is observed mainly by enzymes inhibition of the flavonoid compounds, which are participating in the synthesis of prostaglandins and which are mediators of anti-inflammatory response. Reducing the amount of prostaglandins, inhibit the influx of leukocytes, the tension of the capillaries comes back to normal and thus reduces the inflammatory reaction.
  • Hesperetin (in oranges and lemons), and naringenin (grapefruits and peaches) can protect our skin from excessive UV radiation.
  • Flavonoids included in food can also reduce cancer incidence. This is due to the inhibition of proliferative processes of tumor cells, inducing their process of apoptosis (programmed cell death), and also as a result of the impact of the activity of the enzymes that metabolize xenobiotics. However, it should be noted that the anticancer mechanism of action of flavonoids is not known yet.
  • Some flavonoids may also be potential therapeutic agents in the treatment of AIDS patients. Epicatechin, quercetin, myricetin inhibit reverse transcriptase of an enzyme responsible for the development of HIV.
  • Some flavonoid compounds (e. g., vitamin P) affect on the better hearts work, the process of angiogenesis (formation of new blood vessels) exhibits diuretic properties.
  • At the cellular level, flavonoids are responsible for growth, cell proliferation and differentiation of tissues.

Due to a number of key functions carried out by the flavonoids in the human body, providing adequate amounts of these compounds in the diet is extremely important for the proper functioning of the body. Therefore, flavonoid compounds contained in medicines based on herbs and dietary supplements, are complementary to naturally occurring flavonoids in our diet.

Sources:

  1. Majewska M., Czeczot H. 2009. Flawonoidy w profilaktyce i terapii. Terapia i leki 65(5): 369 – 377.
  2. Miktus M. 2010. Barwy natury – roślinni sprzymierzeńcy witaminy C. Nutrition & Health rocznik 13, nr 2(51): 1 – 12.
  3. Miller E., Malinowska K., Gałęcka E., Mrowicka M., Kędziora J. 2008. Rola flawonoidów jako przeciwutleniaczy w organizmie człowieka. Polski Merkuriusz Lekarski XXIV, 144, 556 – 560.
  4. Oszmiański J. 2007. Prozdrowotne polifenole w chorobach serca i naczyń krwionośnych. Przemysł Fermentacyjny i Owocowo-Warzywny 7-8: 42-43.
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