Health benefits of phytonutrients – flavonoids
Classification, plant sources and health benefits of flavonoids
Flavonoids, otherwise known as bioflavonoids, are a group of secondary metabolites in plants. To explain further, secondary metabolites are organic compounds produced by plants for their defence against herbivores or as colours in flowers that attract birds and insects, for the purpose of pollination. They are not essential to the human body, neither are they involved in reproduction, growth and development of man. However, they are involved in the well being of the human being, as they help to prevent diseases and some may have curative abilities.
Flavonoids can be classified into three major groups: flavonoids (bioflavonoids), iso-flavonoids and neo-flavonoids. These three are also referred to as anthozanthins (flavones and flavonols) because they are ketone-containing compounds. Flavonoids also contain flavanoids. Flavanoids are non-ketone polyhydroxy polyphenol compounds.
Classes of flavonoids and their plant sources
1. Flavonols, (example quercetin, kaempferol, querctagetin etc.), found in apples, broccoli, green and black tea, blueberry, kale, tomato and yellow onions.
2. Flavones, (example luteolin, tangeretin etc.), celery, parsley and pepper.
3. Flavanones, (example navigenin), citrus fruits juices.
4. Flavanols, cocoa and cocoa beverages, dark chocolate.
5. Proanthocyanidins or catechins, apricot, cherry, beans, chocolate, cocoa beverages, grapes, green tea, black tea, peach, red wine and black berry.
6. Isoflavones, soy products such as beans, flower, cheese and Tofu.
7. Anthocyanins, blackberry, black currants, black grape, plum, red cabbage, red wine and strawberry.
Health benefits of flavonoids
There is a complex cascade of reactions in the cells of the body that determine the response of cells to physiological signals or too stressful conditions. Certain proteins are produced which bind to specific receptors on the DNA which influence the pathway known as cell signalling pathway. This is a complicated cascade of events that finally result in either proliferation or death of cells. Flavonoids affect the production and effect of these proteins depending on the desired outcome. It is by the modulating influence of flavonoids on this cell signalling pathway that the health benefits of flavonoids are determined.
The cardiovascular system
Prevention of atherosclerosis: Flavonoids prevent the formation of atherosclerosis in two ways. Firstly, they inhibit the expression of the vascular cell adhesion molecule in the endothelial cells that line the inner layer of the blood vessel. This prevents the deposits of white blood cells released during inflammation; secondly by decreasing inflammation directly.
Increasing endothelial nitric oxide function: Nitric oxide is a relaxer of the smooth muscle on the wall of the artery. By this function, nitric oxide causes vasodilatation of the artery. Flavonoids are known to increase the activity of nitric oxide synthase, the enzyme that catalyses the production of nitric oxide. Vasodilatation reduces the risk of hypertension and other cardiovascular diseases.
Decrease platelet aggregation
Thrombosis is the formation of a blood clot inside a blood vessel. This can be due to injury or other conditions. A thrombus that becomes detached from the wall of the blood vessel and flows freely in the circulation is known as an embolus. An embolus can be big enough to occlude a coronary or a cerebral artery, resulting in either a myocardial infarction (heart attack) or stroke respectively. Platelets are the first components of blood to be released in the formation of a blood clot, a thrombus. Flavonoids inhibit the aggregation of these platelets, thus preventing such serious cardiovascular diseases.
Antioxidant activity of flavonoids
In vitro studies have shown flavonoids to be effective free radical scavengers. However, their effectiveness is checked by the fact that their absorption in the intestines is limited and their metabolism in the cells is very fast. Furthermore, most of the flavonoids in circulation are secondary metabolites, which are not as effective as the primary flavonoids. Also, plasma concentration of flavonoids is not as high as that of other well-known antioxidants. Be that as it may, the antioxidant function of the flavonoids added to that of other antioxidants will surely increase the wellbeing of the individual.
Flavonoids as chelating agents
Flavonoids chelate (bind) such mineral ions as iron and copper. They can be joined to other free radicals to produce more potentially dangerous free radicals. Bound to flavonoids, these ions become unavailable for the production of free radicals. This may contribute to the antioxidant function of flavonoids.