Vitamin K is an essential nutrient your body needs to control blood clotting. The hydrocarbon chains on the tail of the molecule allow it to bond to certain proteins, which creates a blood clotting effect. Most people receive adequate daily vitamin K through diet and vitamin K-producing bacteria present in a human’s intestines. Some types of teas also have a small amount of vitamin K.
Brewed tea generally does not have a lot of vitamin K in it when compared to many other foods. The University of Maryland Medical Center states that tea comes in three main varieties: green, black and oolong. Dried green tea leaves reportedly have a significant level of vitamin K by weight. However, the USDA reports in its nutrient database that both brewed and instant teas have less than 1 mcg of vitamin K per serving.
Research into the effects of vitamin K from tea is somewhat limited as of the publication of this article. A 1999 case report examining a 44-year-old man receiving the blood thinner warfarin for a heart condition found that the patient’s drinking of 1/2 to 1 gallon of green tea daily negatively impacted the effectiveness of the warfarin. When the patient ceased to drink the green tea, the effectiveness of his medication rose again. The researchers concluded that the vitamin K present in the green tea antagonized the warfarin.
Recommended Daily Amount
Though green tea may give you too much daily vitamin K when you drink it to excess, the New York University Langone Medical Center reports that regular consumption of green tea as a beverage in normal amounts does not appear to significantly affect vitamin K levels. The average male adult needs around 120 mcg of vitamin K per day, while the average female needs around 90 mcg. While it is easy to achieve your daily vitamin K needs through foods such as Brussels sprouts and kale, the minuscule amount in any type of tea would have very little effect on your vitamin K, even with multiple servings.
Vitamin K Deficiency
Vitamin K deficiency is a rare condition that inhibits your blood clotting ability and may weaken bone structure over time. If you notice abnormal nose bleeds, bleeding gums, tarry black stools or other bleeding symptoms, you may have a vitamin K deficiency. Because teas are relatively low in vitamin K compared to some other foods, it is unlikely your doctor would prescribe green, black or oolong tea to treat the deficiency. Treatments for vitamin K deficiency commonly include an injection or a dietary supplement.
- Linus Pauling Institute; Vitamin K; Jane Higdon, Ph.D.; May 2004
- University of Maryland Medical Center; Green Tea; David Zieve, M.D., M.H.A. et al.; September 2010
- New York University Langone Medical Center: Green Tea
- "The Annals of Pharmacotherapy"; Probable Antagonism of Warfarin by Green Tea; J.R. Taylor et al.; April 1999