Clinical Information

Vitamin K1, or phylloquinone, is part of a group of similar fat-soluble vitamins in which the 2-methyl-1,4- naphthoquinone ring is common. Phylloquinone is found in high amounts in leafy green vegetables and some fruits (avocado, kiwi). It is a required cofactor involved in the gamma-carboxylation of glutamate residues of several proteins. Most notably, the inactive forms of the coagulation factors prothrombin (factor II), factors VII, IX, and X, as well as protein S and protein C are converted to their active forms by the transformation of glutamate residues to gamma-carboxyglutamic acid (Gla). Other proteins such as those involved in bone metabolism, cell growth and apoptosis also undergo this Gla transformation. Thus, vitamin K plays a critical role in hemostasis (blood clotting) and acute deficiency is characterized by defective blood coagulation. In neonates, low vitamin K levels in breast milk, inadequate placental transport, and hepatic immaturity leading to insufficient synthesis of coagulation proteins can result in the bleeding disorder hemorrhagic disease of the newborn. To minimize this risk, Vitamin K is commonly administered prophylactically immediately after birth. Other at-risk groups for vitamin K deficiency include those with insufficient dietary intake, malabsorption disorders, cystic fibrosis, cholestasis, and alcoholism, as well as liver and pancreatic disease. Several drugs such as coumarin anticoagulants (ie, warfarin) and antibiotics (ie, cephalosporin) have also been shown to interfere with vitamin K metabolism. High doses of vitamin K have not been shown to produce toxicity. Direct measurement of vitamin K1 by liquid chromatography tandem mass spectrometry has been established as a highly effective strategy to assess status and intake.