What is Osteoporosis?

Osteoporosis is a condition in which there is a thinning of the bones, causing them to fracture (break) more easily. It is most often seen in postmenopausal women.

What happens to the bones?

Bone is a living tissue, which is made up of a hard outer shell and an inner honeycomb structure, consisting of tiny collagen fibres and minerals such as calcium and phosphate. These minerals determine the bone mass or density, and are what give bone its strength.

Bone is constantly being renewed by a process called bone remodelling or bone turnover, in order to maintain its strength. Old, worn-out bone is constantly being broken down by a type of bone cell called osteoclasts, and replaced with new, stronger bone by cells called osteoblasts.

During childhood and adolescence, bone is produced faster than it is broken down, leading to an overall gain in bone. The amount of bone in the skeleton reaches its maximum by the mid-20s this is called peak bone mass.

After the mid-30s, bone is broken down faster than it is replaced. A certain amount of decrease in bone density with age is therefore natural. However, in people with osteoporosis, the bone density becomes abnormally low meaning the bones are fragile and more likely to fracture.

What causes osteoporosis?

There are a number of reasons why osteoporosis can develop. A major reason is if the bones were not very strong to begin with (i.e., if peak bone mass was low). If this is the case then osteoporosis will be more likely to develop during the natural decline of bone mass with age.

There are a number of factors which determine peak bone mass, although not all of them are fully understood. They include:

• Calcium intake
• Genetic (hereditary) predisposition
• Physical exercise
• Sex hormones

Osteoporosis can often occur after the menopause in women. This is due to a decline of the female hormone oestrogen, which causes a marked decrease in bone density.

Other medical conditions can also sometimes lead to osteoporosis. These include conditions that affect the absorption of food, such as Crohn's disease, coeliac disease and ulcerative colitis, and conditions that leave you immobile, such as arthritis. Use of corticosteroid tablets can also increase risk of osteoporosis.

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