THE EFFECT OF DIETARY VITAMIN-K ON WARFARIN-INDUCED ANTICOAGULATION

We examined the effect of vitamin-K-rich vegetables, vitamin-K-poor vegetables and phytomenadione on the stability of warfarin-induced anticoagulation. Patients on stable anticoagulant treatment were randomized to either 1 (n = 5), 2 (n = 7) or 7 (n = 13) d with high intake of vitamin-K-rich vegetables (median daily vitamin K intake 1100-mu-g) or high intake of vitamin-K-poor vegetables (daily vitamin K intake 135-mu-g) for 6 d (n = 7), or habitual diet supplemented with 1000-mu-g of phytomenadione daily (n = 5). Nine patients (69 %; 95 % CI, 39-91 %) who consumed vitamin-K-rich vegetables for 7 d reached activities above the therapeutic level. Two (40 %; 95 % CI, 5-85 %) and three patients (43 %; 95 % CI, 10-86 %) who consumed vitamin-K-rich vegetables for 1 and 2 d, respectively, exceeded the upper therapeutic limit. No changes were observed in the vitamin-K-poor group. All patients who received phytomenadione exceeded the upper therapeutic limit. Dietary vitamin K should be regarded as an important environmental factor contributing to unwanted disturbances in warfarin-induced anticoagulation.