From the Linus Pauling Institute's write up on Tea flavonoids:
http://lpi.oregonstate.edu/infocent...html#processing
Toxicity-
Adverse or toxic effects of isolated tea catechins or polyphenols have not been reported in humans. Gastrointestinal disturbances and central nervous system (CNS) stimulation associated with high doses of green tea extract have been attributed to their caffeine content (26).
Drug interactions
Excessive green tea consumption was found to decrease the anticoagulant efficacy of warfarin in one case report (27). It is not known whether this effect was due to tea flavonoids or other components of tea, but it would be prudent for individuals on warfarin to consult their health care provider before taking tea extract supplements or drinking large amounts of green tea (see Tea).
Epigallocatechin gallate (EGCG), a tea catechin, has been found to enhance the efficacy of beta-lactam antiobiotics against methicillin-resistant Staphylococcus aureus bacteria in culture (28). It is not yet known whether taking EGCG or green tea extract will also enhance the efficacy of beta-lactam antiobiotics against methicillin-resistant bacterial infections in humans.
Nutrient interactions
Tea and nonheme iron: Nonheme iron is found in plants, dairy products, and iron supplements, while heme iron comes mainly from hemoglobin and myoglobin in meat, poultry, and fish. The flavonoids in tea are capable of binding nonheme iron and inhibiting intestinal absorption of this form of iron. It has been estimated from a number of controlled trials in humans that nonheme iron absorption is inhibited by about 60-70% in response to the simultaneous consumption of one cup of tea (29). For those at risk of iron deficiency, it would be prudent to consume tea or tea extracts between meals rather than with meals and to avoid drinking tea or taking tea extracts one hour before or two hours after taking iron supplements.
SUMMARY
Processing of tea (Camellia sinensis) leaves determines the type of tea and the characteristic flavonoid content.
Flavonoids found in tea include catechins, theaflavins, tharubigins, and flavonol glycosides.
White and green teas have the highest catechin content, whereas black tea has the highest content of theaflavins and thearubigins.
Although tea flavonoids are effective antioxidants in vitro (in the test tube), the extent to which they increase the antioxidant capacity of humans is unclear.
Tea flavonoids may also stimulate the activity of detoxification enzymes, modulate transcription factor activation and cell signaling pathways, induce cell cycle arrest and programmed cell death (apoptosis), and inhibit tumor invasion and angiogenesis.