Green tea, derived from the leaves of the Camellia sinensis plant, is one of the most widely consumed beverages globally, often sought out for its antioxidant properties. The answer to whether green tea contains Vitamin K is yes, though the quantity and its impact depend heavily on the form consumed. Vitamin K is a fat-soluble nutrient generally abundant in plant chlorophyll, which explains its presence in green tea leaves.
Quantifying Vitamin K Content in Green Tea
Green tea leaves contain a notable amount of Vitamin K, specifically the plant-based form known as phylloquinone (K1). Dry green tea leaves have a high concentration, averaging around 894 micrograms (mcg) per 100 grams of dried leaf material.
However, preparing traditional brewed green tea significantly changes the final intake. Since Vitamin K is fat-soluble, it does not extract well into hot water during steeping. A standard cup of brewed green tea contains a minimal amount, often 0.03 mcg or less per 100 milliliters of liquid.
The concentration changes entirely when consuming powdered green tea, such as Matcha, because the entire leaf is ingested. A typical one-gram serving of Matcha powder can contain between 30 and 58 mcg of Vitamin K. While 100 grams of cooked spinach provides over 500 mcg, the Matcha serving remains a moderate source of the vitamin.
The Biological Role of Vitamin K
Vitamin K is a group of fat-soluble vitamins required for the body to activate specific proteins. The two main forms are Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinone). K1 is synthesized by plants and is the form found in green tea and other leafy greens.
The liver primarily uses K1 to activate coagulation factors, which are proteins essential for blood clotting. Without sufficient Vitamin K, the body cannot form a proper clot, leading to excessive bleeding. K2 is mostly found in fermented foods and animal products and has a longer half-life in the bloodstream.
K2 is important for functions outside of the liver, particularly in bone and cardiovascular health. It helps activate proteins like osteocalcin, which directs calcium into bone tissue, and matrix Gla protein, which prevents calcium from depositing in soft tissues like arteries.
Clinical Relevance: Green Tea and Anticoagulant Medications
The Vitamin K content in green tea becomes clinically relevant for individuals taking anticoagulant medications, particularly Vitamin K antagonists (VKAs) like Warfarin. Warfarin works by competitively inhibiting an enzyme called Vitamin K epoxide reductase complex 1 (VKORC1). This enzyme recycles inactive Vitamin K back into its active form, which is necessary for synthesizing clotting factors.
By blocking this recycling process, Warfarin depletes the supply of active Vitamin K, reducing the production of active clotting factors (II, VII, IX, and X) and thinning the blood. Consuming high amounts of Vitamin K can counteract the medication’s effect, making the blood more prone to clotting.
To manage this interaction, patients on Warfarin must have their clotting time closely monitored using the International Normalized Ratio (INR) test. The therapeutic goal is generally an INR between 2.0 and 3.0. The most important instruction is to maintain a consistent daily intake of Vitamin K, rather than eliminating K-rich foods. Drastically changing the amount of Vitamin K consumed, such as through high-K products like Matcha, can cause the INR to fluctuate dangerously.
Preparation Variables Affecting Vitamin K Levels
The final amount of Vitamin K delivered from green tea is highly dependent on the preparation method, mainly due to the vitamin’s fat-soluble nature. In traditionally brewed green tea, the Vitamin K remains trapped within the tea leaves, which are discarded after steeping. The water-based infusion extracts only a minimal amount of the vitamin, resulting in very low levels in the beverage.
The consumption of Matcha powder represents the highest possible intake because the entire pulverized leaf is consumed. This method ensures that the full nutritional profile, including the fat-soluble Vitamin K, is ingested. Therefore, a person on anticoagulant therapy would need to monitor their intake of Matcha far more closely than they would for regular brewed green tea.
Factors like leaf maturity, steeping time, and water temperature affect the extraction of other compounds. However, the fundamental difference between consuming the water-based infusion and the whole, ground leaf is the deciding factor for Vitamin K intake.