The strength of your bones depends on the amount of minerals laid down in the hard outer shell. This is done through a process called mineralization. Minerals e. g. calcium and phosphorus are absorbed from the food you eat and deposited in your bones. You also need vitamin D for this process because it helps your body to absorb calcium and makes sure it gets to where it's needed (e. g. your bones and teeth). During childhood, mineralization helps your bones to grow and develop whereas in adulthood it maintains and repairs them.
Attribution: BUPA