Flavonoids

Dr. Louay LabbanA’Sharqiyah University

Flavonoids

• Polyphenolic compounds that are ubiquitous in nature and are categorized, according to chemical structure, into flavonols, flavones, flavanones, isoflavones, catechins, anthocyanidins and chalcones

What are flavonols?

• Flavonols are phytochemical compounds found in high concentrations in a variety of plant-based foods and beverages. Based on their structure, flavonols are classified as flavonoids and include the following compounds: quercitin, kaempferol, and myricetin.

• Over 4,000 flavonoids have been identified, many of which occur in fruits, vegetables and beverages (tea, coffee, beer, wine and fruit drinks).

• The flavonoids have aroused considerable interest recently because of their potential beneficial effects on human health they have been reported to have antiviral, antiallergic, antiplatelet, antiinflammatory, antitumor and antioxidant activities.

• Antioxidants are compounds that protect cells against the damaging effects of reactive oxygen species, such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite.

• An imbalance between antioxidants and reactive oxygen species results in oxidative stress, leading to cellular damage. Oxidative stress has been linked to cancer, aging, atherosclerosis, ischemic injury, inflammation and neurodegenerative diseases (Parkinson's and Alzheimer's).

• Flavonoids may help provide protection against these diseases by contributing, along with antioxidant vitamins and enzymes, to the total antioxidant defense system of the human body.

• Epidemiological studies have shown that flavonoid intake is inversely related to mortality from coronary heart disease and to the incidence of heart attacks.

• The recognized dietary antioxidants are vitamin C, vitamin E, selenium, and carotenoids. However, recent studies have demonstrated that flavonoids found in fruits and vegetables may also act as antioxidants.

• Like alphatocopherol (vitamin E), flavonoids contain chemical structural elements that may be responsible for their antioxidant activities. The contribution of flavonoids to the antioxidant defense system may be substantial considering that the total daily intake of flavonoids can range from 50 to 800 mg.

Dosage

• Flavonoid intake depends upon the consumption of fruits, vegetables, and certain beverages, such as red wine, tea, and beer. The high consumption of tea and wine may be most influential on total flavonoid intake in certain groups of people.

• This intake is high compared to the average daily intake of other dietary antioxidants like:

• vitamin C (70 mg)• vitamin E (710 mg) • or carotenoids (23 mg).

Antioxidant flavonoids

• Quercetin (a flavonol in vegetables, fruit skins, onions)

• Xanthohumol (a prenylated chalcone in hops and beer)

• Isoxanthohumol (a prenylated flavanone in hops and beer)

Hops أو الدينار حشيشة

• Genistein (an isoflavone in soy) Prooxidant flavonoids

• Chalconaringenin (a nonprenylated chalcone in citrus fruits)

• Naringenin (a nonprenylated flavanone in citrus fruits)

• The capacity of flavonoids to act as antioxidants depends upon their molecular structure. The position of hydroxyl groups and other features in the chemical structure of flavonoids are important for their antioxidant and free radical scavenging activities.

• Quercetin, the most abundant dietary flavonol, is a potent antioxidant because it has all the right structural features for free radical scavenging activity.

• The antioxidant properties of the prenylflavonoids were compared to those of quercetin (a flavonol), genistein (the major isoflavone in soy), chalconaringenin (a nonprenylated chalcone), naringenin (a nonprenylated flavanone), and vitamin E.

• Xanthohumol, the major prenylchalcone in hops and beer, is a more powerful antioxidant than vitamin E or genistein. However, xanthohumol was less potent than quercetin. The potency of xanthohumol as an antioxidant is markedly increased when combined with an equivalent amount of vitamin E.

• A flavonoid chalcone (chalconaringenin) and a flavanone (naringenin) with no prenyl groups act as prooxidants, i.e. they promote rather than limit the oxidation of LDL by copper. However, adding a prenyl group to these flavonoid molecules counteracted their prooxidant activities.

• The specific amounts of flavonols in foods are affected by a range of factors including plant type and growth, season, light, degree of ripeness, food preparation, and processing.

• Despite these variables, high concentrations of flavonols can be found in apples, apricots, beans, broad beans, broccoli, cherry tomatoes, chives, cranberries, kale, leeks, pear, onions, red grapes, sweet cherries, and white currants .

Beneficial effects associated with consumption of flavonols

• Consumption of flavonols has been associated with a variety of beneficial effects including:

• Increased activity of erythrocyte superoxide dismutase (an antioxidant enzyme found in red blood cells)

• A decrease in lymphocyte DNA damage, a decrease in urinary 8-hydroxy-2’-deoxyguanosine (a marker of oxidative damage),

• An increase in plasma antioxidant capacity (the ability to scavenge free radicals) .

Sources

• Apples: Studies have investigated the relationship between consumption of apples and susceptibility to chronic diseases such as:

• Cancer• CVD• Asthma• Diabetes .

• Broccoli: Cruciferous vegetables are part of the plant family Brassicaceae, which includes:

• Broccoli• Cabbage• Cauliflower• Brussels sprouts• Turnips• Watercress.

• Consumption of this group of plant foods has been associated with a reduction in risk of several cancers including:

• Lung• Breast• Colorectal• Prostate

• Cranberries: Cranberries are commonly touted as a remedy for treating urinary tract infections. Current research has also investigated the relationship between consumption of cranberry products and cancer and cardiovascular disease.