Background—Dietary vitamin K is thought to be an important factor that interferes with anticoagulation stability, but the clinical applicability of this interaction has not been evaluated adequately in prospective studies.

Methods and Results—In a randomized controlled trial that enrolled outpatients with a recent international normalized ratio (INR) outside the therapeutic target, we compared 2 strategies to optimize long-term oral anticoagulation: (1) a conventional approach based on changes in anticoagulant prescription and (2) a dietary vitamin K–guided strategy based on simple modifications of the amount of vitamin K–rich foods ingested per week. The primary efficacy end point was the percentage of patients who achieved a prespecified INR target at 90 days after randomization. Study population (n=132) predominantly included men with mechanical heart prostheses (58%) or atrial fibrillation (35%). Over time, patients allocated to the vitamin K–guided strategy reached the prespecified INR more frequently so that after 90 days of follow-up, 74% were on target compared with 58% of patients managed conventionally (P=0.04). Patients allocated to the dietary vitamin K–guided strategy had the same magnitude and direction of INR variation as those observed with the conventional approach in the short term (15 days) for both underanticaogulated and overanticoagulated patients. Minor bleeding or use of parenteral vitamin K were also marginally less frequent in patients managed according to the dietary intervention (1 [1.5%] versus 7 [11%]; P=0.06).

Conclusions—A vitamin K–guided management strategy to adjust long-term oral anticoagulation is feasible and safe and may result in an increased chance of reaching target levels of INR.