Vitamin K

Vitamin K, the blood-clotting vitamin, is important for the function of numerous proteins within the body, such as the coagulation factors, osteocalcin and matrix-Gla protein. In Vitro: Phylloquinone (vitamin K1) and Menaquinones (vitamin K2) are the two naturally occurring forms of vitamin K. Phylloquionone is the major dietary source of vitamin K and is found at highest concentrations in green leafy vegetables^[1]. Vitamin K2 (menaquinone) is found in small amounts in chicken, butter, egg yolks, cheese and fermented soyabeans. Vitamin K1 and vitamin K2 are required for the γ-glutamyl carboxylation of all vitamin K-dependent proteins^[2]. Vitamin K has important actions in the nervous system. Vitamin K contributes to the biological activation of proteins Gas6 and protein S, ligands for the receptor tyrosine kinases of the TAM family (Tyro3, Axl, and Mer). In brain, vitamin K also participates in the synthesis of sphingolipids, an important class of lipids present in high concentrations in brain cell membranes^[3]. In Vivo: Vitamin K is well-known for its function in blood coagulation. Several human studies report the beneficial role of vitamin K supplementation in improving insulin sensitivity and glucose tolerance, preventing insulin resistance, and reducing the risk of type 2 diabetes^[1]. The adequate intake for vitamin K has been proposed to be 90 µg/day for women and 120 µg/day for men^[2]. Vitamin K deficiency results in an increase in undercarboxylated osteocalcin, a protein with low biological activity. Several studies have demonstrated that low dietary vitamin K intake is associated with low bone mineral density or increased fractures. Additionally, vitamin K supplementation has been shown to reduce undercarboxylated osteocalcin and improve the bone turnover profile^[4].