Submitted to: Thrombosis and Haemostasis
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/23/2013
Publication Date: 7/1/2013
Citation: Li, R.C., Finkelman, B.S., Chen, J., Booth, S.L., Bershaw, L., Brensinger, C., Kimmel, S.E. 2013. Dietary Vitamin K intake and anticoagulation control during the initiation phase of warfarin therapy: A prospective cohort study. Thrombosis and Haemostasis. 110(1):195-196. Interpretive Summary: Variability in vitamin K intake has been attributed to instability in oral anticoagulant therapy. However this has not been well studied. We examined the associations between variability in vitamin K intake and measures of coagulation in a study of 282 patients starting on oral anticoagulant therapy. Those patients who consumed either very low amounts of vitamin K or very high amounts of vitamin K had a greater risk for instability in their oral anticoagulant therapy compared to those who consumed moderate amounts. Daily variability in vitamin K intake did not increase risk of instability of oral anticoagulation therapy. These findings support the evaluation of usual dietary vitamin K intake as a risk factor for unstable anticoagulation when initiating warfarin therapy and suggest that moderate levels of vitamin K intake may be optimal for anticoagulation stability.
Technical Abstract: The effect of varying levels of dietary vitamin K intake on therapeutic International Normalized Ratio (INR) values among patients starting warfarin therapy has not been well studied. We performed a prospective cohort study among 282 patients to explore the independent associations between usual intake of dietary vitamin K and the percent time in therapeutic range (PTTR) of INR target values during the initiation phase of therapy. Compared to subjects in the second quartile of vitamin K intake, both those in the lowest and highest quartiles of vitamin K intake had an increased risk of low PTTR (multivariable odds ratio [OR] = 2.80, 95% confidence interval [CI]: 1.32-5.91; OR = 2.28, 95% CI: 1.06-4.93, respectively). Subjects with lower vitamin K intake also had lower risk of subtherapeutic INR (OR = 0.61 95% CI: 0.39-0.94). These findings suggest that moderate levels of intake may be optimal for therapeutic INR control during the initiation phase of warfarin therapy.