A 59-year-old male presents for follow-up. He is well-known to you, receiving chronic anticoagulation with warfarin for a mechanical aortic valve. His PT and INR have been in the therapeutic range for years. When asked, he denies taking any other medications. He has had no new medical problems and is feeling well. Today his INR is 6.2 (therapeutic range 2.5–3.5). You inquire about dietary changes, focusing on foods rich in vitamin K.

Which of the following is true regarding vitamin K?

The correct answer is B.

 Vitamin K is a fat-soluble vitamin present in leafy green vegetables such as spinach and cabbage and in other foods such as milk, butter, bacon, and vegetable oils. Olive oil and broccoli are particularly rich in vitamin K. Therefore, vegetarians who consume these regularly are not at high risk for developing vitamin K deficiency. Vitamin K deficiency causes a hypocoagulable state resulting in a reduction in clotting factors and elevated prothrombin time and INR, leading to poor clotting ability and hemorrhage. Warfarin does act on vitamin K, but by reducing conversion of vitamin K to its active form rather than reducing absorption.

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