What is osteoporosis?
The word osteoporosis means spongy (porous) bone.
Bone is made up of minerals, mainly calcium salts, bound together by strong collagen fibres. Our bones have a thick, hard outer shell (called cortical or compact bone) which is easily seen on x-rays. Inside this, there’s a softer, spongy mesh of bone (trabecular bone) which has a honeycomb-like structure.
Bone is a living, active tissue that’s constantly renewing itself. Old bone tissue is broken down by cells called osteoclasts and is replaced by new bone material produced by cells called osteoblasts.
The balance between the breakdown of old bone and the formation of new bone changes at different stages of our lives.
- In childhood and adolescence, new bone is formed very quickly. This allows our bones to grow bigger and stronger (denser). Bone density reaches its peak by our mid- to late-20s.
- After this, new bone is produced at about the same rate as older bone is broken down. This means that the adult skeleton is completely renewed over a period of 7–10 years.
- Eventually, from the age of about 40, bone starts to be broken down more quickly than it’s replaced, so our bones slowly begin to lose their density.
We all have some degree of bone loss as we get older, but the term osteoporosis is used only when the bones become quite fragile. When bone is affected by osteoporosis, the holes in the honeycomb structure become larger and the overall density is lower, which is why the bone is more likely to fracture.