Some Facts About Green Tea
Green Tea: What It Is and Why It's Studied
Four different forms of tea (white, green, oolong, and black) come from the same source: the leaves of the Camellia sinensis plant. ("Herbal" tea or tisane is not considered true tea, because it contains no Camellia sinensis leaves and is instead derived from the dried flowers, stems, leaves, or berries of numerous other plants.)
What distinguishes the four types of true tea is how the leaves are processed between the time they are picked and the time they are packaged:
White tea is the produced chiefly from tea leaf buds. Because it is minimally processed, it may exhibit potent disease-fighting potential. To date, however, there is comparatively little research on its health effects.
To make green tea, the leaves are picked and preserved (usually by steaming or baking) to keep them from undergoing the process of fermentation (or oxidation).
To make oolong and black tea, the leaves are picked and exposed to the air for a period of time. During this period, the leaves ferment. Oolong tea is exposed to the sun and allowed to partially ferment; black tea is fermented completely.
The process of fermentation slightlychanges the essential chemical makeup of tea. The longer the leaves are allowed to ferment, the weaker the tea's natural roster of cancer-fighting compounds becomes, while the caffeine content of the tea leaves steadily increases.
Generally, green tea has one-half to one-third thecaffeine of black tea.
Green tea contains several substances collectively called polyphenols that have displayed potent antioxidant effects and other cancer-combating properties. Approximately 90 percent of the polyphenols found in green tea are called catechins (KAT-uh-kins). Green tea contains approximately three times the quantity of catechins found in black tea. The chief catechins found in green tea are:
- epicatechin gallate
- epigallocatechin gallate (also known as EGCG).
EGCG is the most active component in green tea, and is a stronger antioxidant than either vitamin C or E. For this reason, it is the most widely studied green tea compound.
Green Tea Data: A Sampling of the Scientific Literature
Throughout China and Japan, green tea is a staple of the diet, particularly among the older generation. Epidemiological studies (mostly conducted in Asian populations) have consistently associated green tea consumption with lower incidence of many different cancers.