Absorption, Storage, and Metabolism of Vitamin K
Absorption of phylloquinone from the intestine is via the lymphatic system and is therefore decreased in individuals with biliary insufficiency or various malabsorption syndromes. The distribution of vitamin K in various body organs of the rat was first studied with radioactive forms of the vitamin by using both massive and more physiological amounts of phylloquinone. The finding that a significant portion of dietary phylloquinone is subjected to side-chain cleavage to generate menadione is a very important advance in understanding the overall process of vitamin K metabolism. The substantial available literature dealing with the response of various markers of vitamin K status to alterations in vitamin K intake have seldom addressed the question of bioavailability of the vitamin. Substantial amounts of vitamin K are present in the human gut in the form of long-chain menaquinones. Limited information regarding the subcellular distribution of vitamin K within various tissues is available.