International Normalized Ratio Response Subsequent to Modest Increase in Vitamin K Intake in Patients Treated with Warfarin

Background: Warfarin is an effective oral anticoagulant which exert its effect by blocking the utilization of vitamin K. Warfarin therapy requires ongoing monitoring using the international normalized ratio (INR). In this study, effect of modest increase in vitamin K intake from vegetables on INR values was evaluated in warfarin treated patients. Methods: A single-center study involving 24 outpatients (mean age, 62 years) with two last INR in therapeutic range in which INR variations was less than 0.5. Patients were selected based on their VKORC1 1639G→A polymorphism so that 8 patients from each of GG, AA or GA genotypes were recruited. Patients were asked to consume a vegetable mix (including lettuce, peeled cucumber and tomato) containing approximately 100 µg vitamin K (divided in two meals, lunch and dinner) daily for one week when INR response was measured. Results: Daily consumption of vegetable mix decreased patient’s INR from 2.43±0.51 to 2.08± 0.46 (P<0.001). INR value had a significant decrease in each VKORC1 genotypes (from 2.55± 0.55 to 2.21± 0.54 in GG, 2.35± 0.33 to 2.00± 0.25 in AA, and  2.39± 0.65 to 2.00± 0.25 in GA) but the values did not differ between genotypes. Conclusions: Daily increase in vegetable salad containing approximately 100 µg, decreased INR of patients. Therefore, avoiding variation in consumption of foods with even moderate content of vitamin K could help to prevent INR fluctuations in warfarin treated patients.