Vitamin K2(5), also known as menaquinone-5 (MK-5), is a bioactive form of vitamin K2 belonging to the menaquinone family. It features a side chain with five isoprenoid units, contributing to its lipid solubility and role in supporting calcium metabolism. This compound is particularly notable for its involvement in activating proteins such as osteocalcin and matrix Gla-protein, which are critical for bone health and vascular calcification inhibition. Vitamin K2(5) exhibits enhanced bioavailability compared to shorter-chain menaquinones, making it a valuable ingredient in nutraceutical and pharmaceutical formulations. Its stability and efficacy in supporting physiological functions underscore its importance in research and clinical applications.