One of the consequences of growing old is a thinning of the structure of bone and this is called osteoporosis.
It appears to be a natural process which happens to us all but is more common in women and begins after the menopause. In men, the same process seems to develop after 65 but rarely causes problems until the eighties.
Bone is a living tissue and constantly undergoes change. Old bone is resorbed and new bone is laid down. Bone consists of a protein matrix on which calcium salts are deposited and give it strength.
The cause of this problem is still a matter of debate and continued research. Originally, it was thought to be one of failure of adequate protein matrix but now there is evidence that some changes in calcium balance are also involved.
Osteoporosis does not, in itself, cause symptoms, but the thinning of the bones makes them fragile and more easily liable to fracture even from simple injury.