Abstract
Available vitamin K was studied by serial prothrombin tests in ten anticoagulated and ten healthy subjects in one approach to the problem of long-term anticoagulation instability. Dietary manipulations of vitamin K produced a profound and predictable effect on anticoagulation stability. This fat soluble vitamin (K) is apparently not absorbed from the colon, probably the site of most bacterial synthesis. Foods, rather than intestinal bacterial synthesis, probably provide most vitamin K for humans.