Vitamin K is a fat-soluble vitamin essential for activating proteins involved in blood clotting and calcium handling in the body. Its classic role is enabling clotting factors to function properly, helping prevent excessive bleeding. Research also links vitamin K to bone and vascular biology through proteins such as osteocalcin (bone) and matrix Gla protein (MGP), which may influence where calcium is deposited. The main forms are K1 (phylloquinone), abundant in leafy greens, and K2 (menaquinones), found in fermented foods and some animal products. Whether supplementation is needed depends on diet quality, absorption, medications (notably anticoagulants), and individual clinical context.