Vitamin K is so named as it was originally called Koagulationsvitamin.
The body stores about 1 week’s supply of vitamin K.
Vitamin K is a fat-soluble vitamin
Vitamin K is required for the synthesis of six factors in the clotting cascade : factors II, VII, IX, X and the anticoagulants protein C and protein S.
γ -Carboxylation of these factors is carried out by the vitamin K-dependent carboxylase. This reaction subsequently allows calcium binding and the conformational change required to become active. The reaction involves the oxidation of vitamin K. Warfarin works by stopping the reversal of this oxidation.
Bile is required for absorption of vitamin K in the gut.
Menadiol, a synthesized form of vitamin K (K3), is water-soluble and therefore can be absorbed in conditions in which bile secretion is low. But, it is not recommended for use in neonates as it may produce haemolysis.
Haemorrhagic disease of the newborn is caused by a relative vitamin K deficiency.
Prophylaxis against haemorrhagic disease of the newborn is usually given at birth as an injection of the naturally occurring fat-soluble phytomenadione.