If you’re like most people, you think about bones as the dry, stiff specimens you see holding up dinosaur heads in museums or keeping turkey legs together on Thanksgiving. But the bones in your body are a world away from these fossilized and cooked leftovers. They’re still tough and impressively resilient, but they’re built of healthy, living tissue, just like all the other parts of your body. That’s why children can grow taller month after month, and why your body can restore a cracked bone to its original strength. On the darker side of things, that’s also why bones are susceptible to cancer.
You might assume that bones bother changing themselves only at certain times in your life—for example, as you grow through childhood or recover from an injury. But even if you’re an adult with pristine bones, your body is constantly busy breaking them down and rebuilding them in a process called remodeling (which, happily, doesn’t involve unreliable contractors or flighty home decorators).
To perform this ongoing regeneration, your body dissolves small patches of bone one bit at a time, and then fills the resulting holes with new material (sort of like an industrious road-repair crew). Remodeling serves three purposes. First, it fixes microscopic cracks in your bones. Second, it rebalances the strength of your bones, toughening up the parts that you strain most often. And third, it manages your body’s level of important minerals, like calcium.
For example, if you have extra calcium circulating in your blood, your body incorporates it into newly laid-down bone. But if your body is short of calcium, it reclaims the mineral from the chewed-out bone matter as it remodels, and contributes less calcium to the newly patched-up bit. This presents a problem, because without those hard minerals, your bones won’t have their full and proper strength. That’s why a low-calcium diet puts you at increased risk of developing fragile bones.
Remodeling is slow work—in fact, it takes months to fill a single hole. However, you have roughly a million independent repair crews working throughout your body, and together they do enough work to give you a new skeleton every decade of your life.
Source of Information : Oreilly - Your Body Missing Manual