Vitamin K

In 1929, the Danish researcher Henrik Dam first noted that vitamin K played a critical role in blood clotting, and he named it vitamin "K" for "Koagulation." Vitamin K comprises a family of compounds known as quinones. These include phylloquinone from plants and the menaquinones from animal sources. Phylloquinone is the most biologically active form. Menaquinones are also synthesized by bacteria in the colon and absorbed, contributing about 10 percent of total vitamin-K needs. Vitamin-K absorption depends on normal consumption and digestion of dietary fat. It is primarily stored in the liver.

Vitamin K helps in the activation of seven blood-clotting-factor proteins that participate in a series of reactions to form a clot that eventually stops the flow of blood. Vitamin K also participates in the activation of bone proteins, which greatly enhances their calcium-binding properties. Low levels of circulating vitamin K have been associated with low bone-mineral density. Thus, an adequate intake of vitamin K may help protect against hip fractures.

  1. A primary deficiency of vitamin K is rare, but a secondary deficiency may result from fat malabsorption syndrome. Prolonged use of antibiotics can destroy the intestinal bacteria that produce vitamin K, precipitating deficiency in individuals at risk. Newborn infants are born with a sterile intestinal tract and those who are breastfed, may run the risk of vitamin-K deficiency, since breast-milk production takes a few days to establish and breast milk is naturally low in this vitamin. To prevent hemorrhaging, all infants in North America receive injections of vitamin K within six hours of birth.
  2. High doses of vitamin K can reduce the effectiveness of anticoagulant drugs such as warfarin (Coumadin), which is used to prevent blood clotting. People taking these drugs should maintain a consistent daily intake of vitamin K. Megadose supplements of vitamin A and E can pose a risk to vitamin-K status. Vitamin A interferes with absorption of vitamin K, and large doses of vitamin E decrease vitamin K-dependent clotting factors, thus promoting bleeding. Toxicity from food is rare, because the body excretes vitamin K much more rapidly than other fat-soluble vitamins.
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