Summary

Evidence suggests that alterations in the dietary intake of vitaminKcanaffect anticoagulation response towarfarin.It is possiblethat a low and erratic intake of dietary vitamin K is at leastpartly responsible for the variable response to warfarin in patientswith unstable control of anticoagulation. Twenty-six patientswithunstable and twenty-sixwith stable control of anticoagulationcompleted dietary records of all foods and drinks consumedon a daily basis for two consecutive weeks.The meandaily intake of vitamin K in unstable patients was considerablylower than that for stable patients during the study period (29±17 µ g v . 76±40µg).The logarithm of vitamin K intake wasconsistently and significantly lower in the unstable patients thanthe stable patients over the two week period (5.9± 0.4µg v.6.9±0.5µg; p<0.001; 95% CI: 0.7–1.2). Changes in vitamin K intakebetween weeks 1 and 2 of the study were negatively correlatedwith changes in International Normalised Ratio (INR)amongst the unstable patients, however this failed to reach significance(r=-0.25; p=0.22).Daily supplementation with oral vitaminK in unstable patients could lead to a more stable anticoagulationresponse to warfarin.