title: Influence of vitamin K on anticoagulant therapy depends on vitamin K status and the source and chemical forms of vitamin K.
abstract: Warfarin therapy requires close monitoring to avoid excessive bleeding and to maintain the effective therapeutic concentration assessed with the internationalized ratio (INR). High vitamin K intake can decrease the therapeutic effectiveness of warfarin, while poor vitamin K status appears to increase the sensitivity to small changes in vitamin K intake, especially from supplements. Very large amounts of vitamin K from a single meal with vegetables (400 g of vegetables with 700 to 1500 microg of vitamin K1) can measurably change INR, but occasional typical servings (<100 g) would probably have little lasting impact on INR. Warfarin requirements may change in those altering their intake of dark-green vegetables. The 2005 Dietary Guidelines for Americans recommends 3 cups/week of dark-green vegetables, which contain about 100 to 570 microg/serving of vitamin K1. Less well-known sources and chemical forms of vitamin K, such as MK-7 in natto (a fermented Japanese product), also measurably influence INR. Additional research is needed in warfarin-treated patients to fully quantify the interactions among various sources and chemical forms of vitamin K, age, genotype, and other factors.
authors.affiliation: Department of Foods and Nutrition and Faculty of Gerontology, The University of Georgia, Athens, Georgia 30602, USA. mjohnson@fcs.uga.edu
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Johnson
mesh_terms: D000925:Anticoagulants / Q000378:metabolism / Q000627:therapeutic use; D000933:Antifibrinolytic Agents / Q000008:administration & dosage / Q000737:chemistry* / Q000494:pharmacology*; D003374:Coumarins / Q000378:metabolism / Q000627:therapeutic use; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D019934:International Normalized Ratio; D014812:Vitamin K / Q000008:administration & dosage / Q000737:chemistry* / Q000494:pharmacology*; D014859:Warfarin / Q000378:metabolism / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D000933:Antifibrinolytic Agents; D003374:Coumarins; D014812:Vitamin K; D014859:Warfarin