Vitamin K and stability of oral anticoagulant therapy

Abstract

One of the causes of unstable anticoagulation is a variable vitamin K intake. The main objective of this thesis was to test the hypothesis that the INR is particularly sensitive to changes in vitamin K intake when vitamin K status is low, and that patients with a low vitamin K intake would therefore have an increased risk of unstable anticoagulation. We approached this problem in three ways. We looked at the effects of dietary vitamin K intake, of vitamin K status as assessed by serum assays and of administration of a vitamin K supplement. Our results confirm the hypothesis that a high vitamin K intake leads to a more stable anticoagulant control. These findings are important to direct the dietary advice that should be given to patients using vitamin K antagonists. Because vitamin K is found chiefly in vegetables the most practical advice would be to maintain a healthy diet containing sufficient fruits and vegetables. The beneficial effect of a vitamin K supplement seems too low to recommend vitamin K supplementation in all users of vitamin K antagonists, but may be worthwhile in unstable patients or patients with a low vitamin K intake.