Influence of Usual Dietary Vitamin K Intake on Anticoagulation Outcomes

Abstract

Vitamin K (VK) is known to interact with warfarin, but its effect on anticoagulation outcomes remains unclear. We aimed to determine whether dietary VK intake was associated with International Normalized Ratio (INR) stability, INR frequency and warfarin stabilization dose in 245 new warfarin users. We also examined whether these associations were modulated by CYP2C9 and VKORC1 variants. Dietary VK intake was assessed using a specific food frequency questionnaire. The %time in the target range (TTR) and the number of INR tests were measured during the 3-12 months after initiation of warfarin and tested with logistic regression models. The warfarin dose was self-reported and tested with a multiple linear regression model. Compared with patients in the lowest third, those in the highest third of VK intake presented a lower risk of having a TTR <60% (OR[95%CI]; 0.43[0.19-0.95]) and >10 INR tests (OR[95%CI]; 0.48[0.23-0.99]), and had a warfarin stabilization dose on average 0.7 mg higher (p=0.04). No statistical interaction was found between VK intake and genetic factors on outcomes (p蠅0.05). Our results suggest that high VK intake benefits on INR stability and frequency, and is associated with a moderately higher warfarin dose. Its effects were not modulated by CYP2C9 and VKORC1 variants in the post-stabilization phase. CL received a studentship from the Fonds de recherche du Québec-Santé.