Any of several fat-soluble compounds essential for the clotting of blood.
A deficiency of vitamin K in the body leads to an increase in clotting time. In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagulation of the blood; its letter name comes from the Danish word koagulation . A pure form was isolated and analyzed structurally in 1939; several related compounds having vitamin-K activity have since been isolated and synthesized. The form of vitamin K that is important in mammalian tissue is of microbial origin. A synthetic vitamin K precursor called menadione is used as a vitamin supplement.