Vitamin K: dietary forms, bacterial sources, and antagonists
THE CONTEXT
Vitamin K is required for synthesis of blood-clotting proteins. Its antagonists reduce coagulation, while its biologically active forms arise from dietary, bacterial, and synthetic sources.
Coagulation and antagonists
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Dicumarol is a vitamin K antagonist associated with hemorrhagic sweet clover disease in cattle.
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Vitamin K antagonists reduce blood coagulation in patients at risk of thrombosis; warfarin is the most widely used antagonist described.
Sources and forms
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Phylloquinone is the normal dietary source of vitamin K and is found in green vegetables.
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Intestinal bacteria synthesize menaquinones, which have side chains of differing lengths.
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Menadione and menadiol diacetate are synthetic compounds.
Limits of bacterial contribution
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Menaquinones are absorbed to some extent, but their biological contribution is uncertain.
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Signs of vitamin K deficiency can be induced by a phylloquinone-deficient diet even when intestinal bacterial action is not inhibited.