In a nutshell: Vitamin K2 makes calcium work.

Bone is comprised of a hard outer shell and spongy inner tissue matrix, which is a living substance. The entire skeleton is replaced every seven years. This process is regulated by osteoblasts, cells that build up the skeleton, and osteoclasts, cells that break down the skeleton. As long as the bone-­‐forming activity (absorption) is greater than the bone-­‐breakdown (resorption), the process of maintaining healthy bones will be kept under control.

Osteoblasts produce a vitamin K-­‐dependent protein called osteocalcin. This protein helps bind calcium to the bone matrix, leading to increased bone mineral content. Consequently, the skeleton becomes more resistant and less susceptible to fracture. Osteocalcin needs vitamin K2 to function optimally.