Osteoporosis is a condition that affects the bones, causing them to become thin and weak.
Approximately three million people in the UK have osteoporosis, and there are over 230,000 fractures every year as a result.
Osteoporosis happens more commonly in old age when the body becomes less able to replace worn-out bone. Special cells within the bones, called living bone cells, are no longer able to break down old bone and renew it with healthy, dense new bone.
As you get older, you also lose a certain amount of bone, causing the bones to become thinner. The bones become fragile and more likely to break (fracture), particularly the bones of the spine, wrist and hips.
Bone is a living tissue that is constantly repairing itself. It is made of a hard outer shell, which contains a mesh of collagen (tough elastic fibres), minerals, blood vessels and bone marrow. This mesh looks a bit like a honeycomb, with spaces between the different parts. Healthy bones are very dense, and the spaces within bones are small. In bone affected by osteoporosis, the spaces are larger, making the bones weaker and less elastic.
Bones are repaired and reinforced by a range of proteins and minerals, which are absorbed from the bloodstream. They include calcium, phosphorus, proteins and amino acids. The growth of sex hormones controls the amount of mineral substance deposited in the bones. Changes in hormone levels can therefore affect the strength of the bones. For example, the female hormone oestrogen offers some protection against osteoporosis. After the menopause, oestrogen levels fall, often causing the bones to thin quickly.
