One nutrient that can lessen warfarin's effectiveness is vitamin K. It's important to be consistent in how much vitamin K you get daily. The adequate intake level of vitamin K for adult men is 120 micrograms (mcg). Vitamin K 2, the main storage form in animals, has several subtypes, which differ in isoprenoid chain length. These vitamin K 2 homologues are called menaquinones, and are characterized by the number of isoprenoid residues in their side chains. Why Vitamin K Can Be Dangerous if You Take Warfarin. Your diet affects how your medications work, especially for patients taking blood thinners such as Coumadin® (warfarin). Vitamin K. Vitamin K is a necessary participant in synthesis of several proteins that mediate both coagulation and anticoagulation. Vitamin K deficiency is manifest as a tendency to bleed excessively. Vitamin K and Warfarin: What You Should Know Marie B. Walker Henry I. Bussey, Pharm.D., FCCP, FAHA May, 2004 Updated January, 2008 Many people recognize that there is a relationship between warfarin and vitamin K, but often, they do not fully understand this relationship. REFERENCES. Food and Nutrition Board of the Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron. Warfarin is an anticoagulant medication. This means it helps prevent clots from forming in the blood. Blood thinners treat some types of heart disease. Potential Interaction Between Warfarin and High Dietary Protein Intake Lori B. Hornsby, Pharm.D., E. Kelly Hester, Pharm.D., and Amy R. Donaldson, Pharm.D. Introduction Vitamin K, the generic name for a family of compounds with a common chemical structure of 2-methyl-1,4-naphthoquinone, is a fat-soluble vitamin that is naturally present in some foods and is available as a dietary supplement. These compounds include phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2). The MK-4 form of vitamin K 2 is produced by conversion of vitamin K 1 in the testes, pancreas, and arterial walls. While major questions still surround the biochemical pathway for this transformation, the conversion is not dependent on gut bacteria, as it occurs in germ-free rats and in parenterally administered K 1 in rats.