Plants produce anti-oxidant components called polyphenols that have a vital role in preventing human disease and act as a preventative measure for human health. Polyphenols are defined as secondary metabolites of plants and offer protection against development of cancers, cardiovascular diseases, diabetes, osteoporosis and neurogenerdative diseases.
Over 8,000 compounds have been identified as polyphenols and include flavonoids, stilbenes and lignans and occur in different concentrations in different areas of the plant. Polyphenolic content of the foods are greatly affected by environmental factors as well as by soil type, sun exposure, rainfall etc.
Epidemiological studies have shown an inverse association between the risk of chronic human diseases and the consumption of polyphenolic rich diet; in other words higher consumption of fruits and vegetables is linked to a lower risk of immune related diseases. The anti-oxidant activity of polyphenols is specifically linked to preventing oxidative cell damage which is limited to various degenerative diseases including coronary heart diseases and various immune diseases.
Some of the most abundant polyphenols include quercetin, found in onion, and which has been shown to be inversely associated with mortality from coronary heart disease. Tea catechin, found in Tea, have been shown to inhibit the invasion and proliferation of the smooth muscle cells in the arterial wall, a mechanism that may contribute to slow down the formation of the atheromatous lesions. Theaflavins and thearubigins, the abundant polyphenols in black tea have also been shown to possess strong anticancer properties and have been found to promote cell death in
Reservatrol, found in red wine or non-alcoholic wine and in red grapes and peanuts reduces bleeding time and platelet aggregation of blood cells. Consumption of black tea increases artery dilation 2 hours after intake and consumption of 240 mL red wine for 30 days countered the cell dysfunction induced by a high fat diet and is associated with lowering blood pressure. Long term regular intake of black tea was found to lower blood pressure in a cross-sectional study of 218 women above 70 years of age. Reservatrol has also been linked to lowering the risk of dementia and Alzheimer’s disease by 80%
In a similar manner development of cancer may be impacted by polyphenol consumption and is associated with a reduction of tumors and reduction of cell growth observed at various sites, including mouth, stomach, duodenum, colon, liver, lung, mammary gland or skin. Many polyphenols, such as quercetin, catechins, isoflavones, lignans, flavanones, ellagic acid, red wine polyphenols, resveratrol and curcumin have been tested and are associated with a positive health impact.
Theaflavins and thearubigins, the abundant polyphenols in black tea have also been shown to possess strong anticancer property. Black tea polyphenols were found to inhibit proliferation and increase cell death in carcinogenic cell.
Polyphenol activity has been associated with impacting on diabetes. Studies have shown that several physiological parameters of the body get altered in the diabetic conditions. Numerous studies report the antidiabetic effects of polyphenols. Tea catechins have been investigated for their anti-diabetic potential.
Polyphenols may affect glycemia through different mechanisms, including the inhibition of glucose absorption in the gut or of its uptake by peripheral tissues affected by individual polyphenols, such as (+)catechin, (−)epicatechin, (−)epigallocatechin, epicatechin gallate, isoflavones from soyabeans, tannic acid, glycyrrhizin from licorice root, chlorogenic acid and saponins also decrease S-Glut-1 mediated intestinal transport of glucose.
Some of the flavanoids called anthocyanins, are highly abundant in brightly colored fruits such as berry fruits and concord grapes and grape seeds. Anthocyanins are responsible for the colors in fruits, and they have been shown to have potent antioxidant/anti-inflammatory activities.
Fruit and vegetable extracts that have high levels of flavonoids also display high total antioxidant activity such as spinach, strawberries and blueberries. It is reported that the dietary supplementations, (for 8 weeks), with spinach, strawberry or blueberry extracts in a control diet were also effective in reversing age-related deficits in brain and behavioral function in aged rats. A recent study demonstrates that the tea catechins carry strong anti-aging activity and consuming green-tea rich in these catechins, may delay the onset of aging.
Polyphenols also provide a neuro-protective effect and influence and modulate several cellular processes such as neurological signaling, proliferation, apoptosis, redox balance and differentiation and impact on a number of neurogenerative dseases such as Parkinson’s, Alzheimer’s disease and dementia.
Other health effects have been observed in asthma cases, obstructive lung disease, osteoporosis, skin damages induced from sunlight, and anti HIV-1 activity.