Vitamin K supplementation improves stability of anticoagulation

Clinical Question

Can vitamin K supplementation help achieve stable control of anticoagulation in adults taking warfarin?

Bottom Line

Vitamin K supplementation can help achieve control of anticoagulation in adults with unexplained instability of response to warfarin. This may be a welcome relief to frustrated patients, clinicians, and staff. (LOE = 1b)


Sconce E, Avery P, Wynne H, Kamali F. Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin. Blood 2007;109(6):2419-23.  [PMID:17110451]

Study Design

Randomized controlled trial (double-blinded)


Unknown/not stated




Outpatient (specialty)


Anticoagulation that is difficult to control in adults taking warfarin may be due to an irregular intake of foods that contain vitamin K. These investigators identified 70 warfarin-treated adults with unstable anticoagulation, defined as having a standard deviation of INR values greater than 0.5 (indicating a wide swing in values) and at least 3 warfarin dose changes in the previous 6 months. Eligible patients randomly received vitamin K (150 ug daily) or matched placebo in a double-blind fashion (concealed allocation assignment). Individuals masked to treatment assignment assessed outcomes. Complete follow-up occurred for 97% of the patients at 6 months. Using intention-to-treat analysis, stable anticoagulation control occurred in significantly more patients taking vitamin K supplementation than in patients taking placebo (54% vs 21%; number needed to treat = 3; 95% CI, 2-10). Daily warfarin dose requirements also increased in significantly more patients in the vitamin K group than in patients in the placebo group (16% vs 1.5%, respectively). No adverse events occurred in either treatment group.