Vitamin K1 (phylloquinone) is strongly tied to blood-clotting function. It is required in the liver to activate clotting factors so bleeding can be controlled properly. K1 is abundant in leafy greens, and most people can meet needs through regular vegetable intake. Functional deficiency can still occur with fat-malabsorption, reduced bile flow, prolonged antibiotics, or significant liver disease. In people taking warfarin, K1 intake should be kept consistent and managed with INR targets.