Sabtu, 12 Juli 2008

Antioxidant, Aging Process, and Green Tea

Aging is a progressive decline of the efficiency of physiological processes after the reproductive phase of life. There are many various theories proposed to explain aging. The free-radicals theory of aging is one of theories which propose that normal aging results from random deleterious damage to tissues by free radicals which are always produced during normal metabolism in the human body, while endogenous antioxidant defenses are not sufficient to counteract them completely. Diet-derived antioxidants may therefore be particularly important in protecting against chronic diseases.
Tea (black and green tea) is an important source of flavonoids in the diet and the flavonoids found in tea are known to be strong antioxidants. It is assumed that the high levels of flavonoids found in green and black tea can protect cells and tissues from oxidative damage by scavenging oxygen free radicals The major flavonoids present in green tea include catechins such as epicatechin(EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG). The relative catechin content of tea is dependent upon how the leaves are processed prior to drying as well as geographical location and growing conditions.
The flavonoid concentration of any particular tea beverage depends upon the type of tea (blended, instant) and preparation (amount used, brew time, temperature). The highest concentration of flavonoids are found in brewed hot tea, less in instant preparations, and lower in ready-to-drink tea.
There are controversial outcomes from different studies regarding the health effects of tea which may be due to lack of data of tea preparation from epidemiological studies. Investigations on standardized tea or tea extracts and controlling tea preparation are needed to clarify the assumption of beneficial effects of tea.
The scientific support is strongest for the protection of DNA from oxidative damage after black and green tea consumption. However, the quality of the studies now available is insufficient to draw a strong conclusion Further evidence from human intervention studies is required.

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