Role of dietary vitamin K intake in chronic oral anticoagulation: Prospective evidence from observational and randomized protocols

PURPOSE: The potential association between vitamin K intake and coagulation instability has been explored primarily in case reports and small, retrospective, uncontrolled studies. We prospectively evaluated the effects of dietary vitamin K intake on anticoagulation parameters. METHODS: In an observational protocol, clinical characteristics and vitamin K intake, assessed semiquantitatively, were evaluated in 39 outpatients who made 230 visits to our anticoagulation clinic. In a randomized crossover protocol, 12 patients with stable anticoagulation underwent 4-day in-hospital dietary interventions, I to 2 weeks apart, providing a 500% increase and an 80% decrease in vitamin K intake relative to the baseline level. RESULTS: Univariate analysis of the observational data demonstrated a progressive, statistically significant inverse association between the vitamin K intake score and different levels of anticoagulation. Multivariate logistic regression analysis showed that vitamin K intake was independently associated with both overcoagulation and undercoagulation. In the randomized protocol, the international normalized ratio increased from 2.6 +/- 0.5 at baseline to 3.3 +/- 0.9 at day 7,(P = 0.005) in subjects on the vitamin K-depleted diet and decreased from 3.1 +/- 0.8 at baseline to 2.8 +/- 0.6 at day 4 (P = 0.04) in those on the vitamin K-enriched diet. CONCLUSION: Our prospective data strengthen the concept that the interaction between vitamin K and coumarin is a clinically relevant, major independent factor that interferes with anticoagulation stability. (C) 2004 by Excerpta Medica Inc.