MedTerms Medical Dictionary

Deficiency, vitamin K: A lack of vitamin K resulting in an increase in the clotting time of the blood, impaired clotting and a tendency to excessive bleeding. Blood clotting is delayed or prevented because vitamin K is unavailable to act as an essential element (a cofactor) in the body's production of four necessary coagulation (clotting) factors (especially prothrombin and also coagulation factors VII, IX, and X).

There are two naturally occurring forms of vitamin K -- vitamin K1 and vitamin K2. Vitamin K1 is made by plants, whereas vitamin K2 is of bacterial origin and is the important form for people. All other forms of vitamin K are converted to vitamin K2 in the body. There are a number of closely related compounds of the vitamin K2 series.

Under natural circumstances, vitamin K deficiency is only rarely encountered. This is because an adequate supply of the vitamin is usually present in the diet and the vitamin is also synthesized by bacteria in the intestine.

Deficiency of vitamin K may, however, occur following the administration of certain drugs that inhibit the growth of the vitamin-synthesizing bacteria or as a result of disorders affecting the production or flow of bile which is necessary for the intestinal absorption of vitamin K.

In newborn babies, the absence of large intestinal bacteria coupled with the absence of body stores of vitamin K may result in hemorrhagic disease of the newborn. This is a dangerous condition because there can be bleeding into critical organs such as the brain. This disorder can be prevented by the administration of vitamin K to the baby shortly after birth or during labor to the mother.

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