Vitamin K is a fat soluble vitamin important for production of various factors in the coagulation cascade and thus helps in preventing prolonged bleeding. It is also called as anti-hemorrhagic factor.
Functions: Vitamin K is absorbed from the small intestine with help of bile secreted by the liver. It is incorporated into the chylomicrons and reaches the liver through the portal circulation where it helps in formation of vitamin K dependent factors such as Factor II, VII, IX and X. Protein C and S also require vitamin K for their activity.
Food Sources: Two forms of vitamin K exists: vitamin K1 or phylloquinone and vitamin K2 or menaquinone. Phylloquinones are derived from vegetables and animal sources. Menaquinone is synthesized from the gut flora.
Recommended daily allowance: Upto 1 year = 2-2.5mcg/d, 1-18 years=50-75mcg/d
Deficiency: Vitamin K deficiency presents as easy bruisability, mucosal bleeding, malena or even CNS bleeds. In newborns, due to immature liver and low vitamin K in breast milk, it can lead to hemorrhagic disease of newborn (HDN). This can lead to bleeding manifestations. typically presenting in the first week of life. Late HDN can occur due to excessive use of antibiotics, cystic fibrosis, biliary atresia, cholestatic hepatitis, celiac disease and chronic warfarin exposure which decreases gut production or absorption of vitamin K. Diagnosis is established by markedly prolonged partial thromboplastin time (PTT) and Prothrombin time (PT) and presence of PIVKA (proteins induced in vitamin K absence- These are non carboxylated forms of Vitamin K dependent factors).
Overdosage: Vitamin K toxicity is very rare. Menadione can cause hemolytic anemia, hyperbilirubinemia, jaundice and kernicterus in infants.