Last updated: 04 October 2011
Osteoporosis is a condition that affects the bones, causing them to become weak and fragile and more likely to break (fracture). These fractures most commonly occur in the spine, wrist and hips but can affect other bones such as the arm or pelvis.
Approximately 3 million people in the UK are thought to have osteoporosis, and there are over 230,000 fractures every year as a result. Although commonly associated with post-menopausal women, osteoporosis can also affect men, younger women and children.
Bone is made of a hard outer shell with a mesh of collagen (tough elastic fibres), minerals (including calcium), blood vessels and bone marrow inside. This mesh looks a bit like a honeycomb, with spaces between the different parts. Healthy bones are very dense, and the spaces inside the bones are small. In bone affected by osteoporosis, the spaces are larger, and this makes the bones weaker, less elastic and more likely to break
Bone is a living tissue that is constantly repairing itself. This process is called bone turnover. There are cells which break down old bone (osteoclasts) and cells which build new bone (osteoblasts). This process requires a range of proteins and minerals, which are absorbed from the bloodstream.
In childhood, bones grow and repair very quickly, but this process slows down as you get older. Bones stop growing in length between the ages of 16 and 18, but continue to increase in density until you are in your late 20s. From about the age of 35, you gradually lose bone density. This is a normal part of ageing, but for some people it can lead to osteoporosis and an increased risk of fractures.
Continue to next section: Symptoms of osteoporosis