Green Tea
Background and Health Claims
Tea is the most commonly imbibed drink around the world after water. Both green tea (which accounts for 20% of consumption) and black tea (which accounts for 80%) are prepared from leaves of the same plant. Black tea leaves have been fermented and roasted. Green tea comes from tea leaves that have been exposed to high temperatures to deactivate fermenting enzymes.
Green tea is thought to protect against cancer by causing cell cycle arrest (which stops cancer cells from dividing wildly) and by inducing cell death (which kills tumor cells). The four major active ingredients in green tea are eipicatechin-3-gallate, epigallocatechin, epicatechin and epigallocatechin-3-gallate (EGCG). EGCG is the most researched, and it is a potent antioxidant. A cup of green tea contains about 10-142 mg EGCG and 10-90 mg caffeine. Black tea has less EGCG than green tea.
Animal studies have shown that oral consumption of EGCG offers protection against all stages of carcinogenesis. Epidemiologic studies have demonstrated that green tea consumption protects against cancer at certain sites, including prostate, bladder, stomach and esophagus.
Precautions
Studies of green tea in cell lines showed cell death in cancer cell lines but not in normal cell lines. This selectivity needs to be studied in humans before a clear conclusion can be drawn regarding whether to avoid or use green tea while undergoing oxidative cancer treatments, such as radiation therapy or chemotherapy.
Although several studies have shown protection against esophageal cancer at normal temperatures, ingestion of very hot tea (55-67o C) was associated with a two- to three-fold increase in the risk of esophageal cancer. One study reported that greater than five cups per day was associated with an increased risk of pancreatic cancer.
While drinking green tea does not appear to be harmful, patients being treated with radiation or chemotherapy should consult their doctor before injesting large amounts of the liquid. Drinking large amounts of one type of beverage may cause people to feel full and therefore decrease their consumption of other nutrient-rich foods and beverages. Cancer patients should be careful to avoid any activity that might decrease their nutritional intake.
Dose
There is no recommended dose for green tea; however, two to five cups per day is probably a safe recommendation. Tea should be steeped one to three minutes.
This therapy also has been reviewed by the MD Anderson Complimentary/Integrative Medicine Education Resources (CIMER) team of faculty and staff researchers.