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Vitamin K
Vitamin K content in green tea:
Green tea extract, which contains vitamin K, may prevent clotting of the blood and thus limit the effect of warfarin. (3)
Taylor JR et al reported that a 44-year-old white male taking warfarin and one-half to one gallon of green tea per day. The PTINR went from 3.79 to 1.37 while drinking ½ to 1 gallon of green tea per day and dropped to as low as 1.14. Removal of the green tea caused normalization of his blood tests with a PTINr of 2.55. Those taking green tea and warfarin together should keep an accurate consistent intake of vitamin K containing foods to maintain therapeutic range of the INR. It was stated by the author that the concentration of the vitamin K in green tea depends on the amount of the green tea leaves brewed and the amount of green tea consumed which was a large amount in this case. Black tea leaves contain only about 18% of the amount of vitamin K found in green tea leaves. (4)
