Vitamin K is a fat-soluble vitamin that functions as a cofactor in the production of blood coagulation factors (in the liver), osteocalcin (in bone), and matrix Gla-proteins (in cartilage and vessel walls), each resulting in the deposition of ionic calcium.
Monitoring vitamin K can help reduce risk of osteoporotic bone fractures, cardiovascular disease, and possibly some cancers by identifying individuals who may have a vitamin K deficiency. Since current dietary recommendations of vitamin K are based on saturation of the coagulation system, those recommendations may be insufficient to maintain vascular and bone health, since individual functions are independent of each other.
Direct vs. functional measurement of vitamin K
The Metametrix Vitamin K Assay measures a functional marker, undercarboxylated osteocalcin (ucOC). Very little vitamin K is stored in the body therefore direct measurement is not ideal.
Osteocalcin (OC) is almost exclusively a product of mature, active osteoblasts and is a vitamin K-dependent, Ca+2 binding protein. A vitamin K deficiency is indicated by an ucOC increase in circulating blood and urine. Therefore, high ucOC indicates low vitamin K status.
There are two natural forms of vitamin K, which differ based on their phytyl group-phylloquinone (vitamin K1) synthesized from plants, and menaquinone (vitamin K2) from bacteria in the large intestines.