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Why are newborn infants at risk for bleeding related to vitamin K deficiency?

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Fibrin in blood clotting — bleeding and blood clotting Red blood cells (erythrocytes) trapped in a mesh of fibrin threads. Fibrin, a tough, insoluble protein formed after injury to the blood vessels, is an essential component of blood clots.

Newborn infants are at risk for bleeding related to vitamin K deficiency primarily because they lack the necessary internal stores and biological mechanisms to maintain adequate levels of the vitamin shortly after birth.1

Specifically, this vulnerability arises from three main factors:
* Absence of intestinal bacteria: Unlike older children and adults, who obtain a significant portion of their vitamin K from bacteria in the intestines, newborns have not yet established these bacterial populations.1
* Limited dietary intake: Breast milk typically contains low levels of vitamin K, which may not be sufficient to meet the infant's needs.1
* Lack of body stores: Infants are often born without significant pre-existing reserves of the vitamin.1

This deficiency can lead to a condition known as hemorrhagic disease of the newborn, which is characterized by spontaneous internal or external bleeding. Because vitamin K is essential for the liver to synthesize prothrombin and other blood clotting factors, its absence impairs the body's ability to stop bleeding. This condition is typically prevented by administering vitamin K to the infant shortly after birth.21