The average human body contains about 1.5 kg of calcium. Major part of the calcium is in the bones as a major part of bone mass.
Bone structure, we could compare with reinforced concrete.
Bone has fibers called collagen fibers, similar to the flexible and iron wires that are placed in reinforced concrete. Calcium makes mass which surrounds the collagen fibers.
The amount of calcium in our bones changes with age.
During the first year of life the child bones have very little calcium and are very flexible. The child can bend in all sorts of directions without breaking any bones. But when one experiences the age of 80, his bones can contain nearly 80 percent of calcium, and are easily breakable.
To young children we give a lot of milk, among other things, because the milk is very rich in calcium, and young organism is, of course, in need a lot of calcium. One liter of cow's milk contains more than 1.5 g of calcium. Cheese, cream and yogurt also contain large amounts of calcium.
In those parts of the world where the food does not have enough calcium people do not have healthy teeth and often suffer from bone fractures.