Vitamin K is necessary for the formation by the liver of prothrombin, Factor VII (proconvertin), Factor IX, and Factor X, all of which are important in blood coagulation. Therefore, when vitamin K deficiency occurs, blood clotting is retarded.
Several compounds, both natural and synthetic, exhibit vitamin K activity. Because vitamin K is synthe-sized by bacteria in the colon, it is rare for a person to have a bleeding tendency because of vitamin K defi-ciency in the diet. However, when the bacteria of the colon are destroyed by the administration of large quan-tities of antibiotic drugs, vitamin K deficiency occurs rapidly because of the paucity of this compound in the normal diet.