*Geek Box: The Vitamin K Cycle
Yes, vitamin K has it’s own ‘cycle’, which makes it one of those cooler nutrients. Vitamin K differs to other fat-soluble vitamins, which are generally stored in the body long-term, and the body stores very little vitamin K. As a result, in the absence of dietary intake, vitamin K can deplete to deficiency. The vitamin K cycle provides the body with a mechanism to recycle vitamin K, allowing small amounts to be used over and over. In tis cycle, vitamin K is oxidised to form vitamin K epoxide. This allows the enzyme for which vitamin K is a cofactor – γ-glutamylcarboxylase (GGCX) – to convert the amino acid glutamic acid (Gla) into y-carboxyglutamic acid [Gla], which is important for blood clotting factor proteins. Vitamin K epoxide can in turn be recycled back to hydroquinone, which is the reduced form, and is then available for further cycling. You may have heard of the anticoagulant drug, warfarin: this drug acts as a vitamin K antagonist by inhibiting the activity of one of enzymes which recycles vitamin K, thus preventing the cycle from producing proteins necessary to form blood clots.