The amount of peak bone mass you reach depends largely on your genes. Then gradually, with age, the breakdown outpaces the buildup, and in late middle age bone density lessens when needed calcium is withdrawn from bone for such tasks as blood clotting and muscle contractions, including beating by the heart. As a teenager, though, you can make the most of things you do control that can build your bones and help reduce the risk of fractures when you are older. The main mineral in bones is calcium, one of whose functions is to add strength and stiffness to bones, which they need to support the body. To lengthen long bones during growth, the body builds a scaffold of protein and fills this in with calcium-rich mineral.
Bone also needs vitamin D, to move calcium from the intestine to the bloodstream and into bone.
Also needed are vitamin A, vitamin C, magnesium and zinc, as well as protein for the growing bone scaffold. Mother Nature provides many foods with these nutrients. Milk is rich in calcium and high-quality protein. Nearly all U.S. milk has vitamins D and A added. And it has magnesium and zinc.