From all K-vitamins, menaquinone-7 has been identified as the most effective cofactor for the carboxylation reaction of Gla-proteins. In this respect it is important to quantify the dose-response relationship of the interaction between oral anticoagulants and menaquinone-7. The primary objective of the study is to demonstrate at what menaquinone-7 intake the vitamin will interfere with oral anticoagulants in a clinically relevant way. Clinically relevant is defined as a decrease in level of anticoagulation that would require a change in oral anticoagulant treatment in order to stay within target levels. Secondary objective of the study is to investigate changes in carboxylation level of osteocalcin and matrix-gla protein after menaquinone-7 supplementation during the oral anticoagulation treatment period. This will demonstrate whether during oral anticoagulation menaquinone-7 will be transported preferentially to the liver or to other target tissues.