The word 'osteoporosis' literally means 'porous bone'. It is a condition where a person gradually loses bone material so that his or her bones gradually become more fragile. As a result, they are more likely to break.
Bone is made of fibres of a material called collagen filled in with minerals - mainly calcium salts - rather like reinforced concrete. The bones of the skeleton have a thick outer shell or 'cortex' inside which there is a meshwork of 'trabecular' bone.
Our bones grow during childhood and adolescence and are at their strongest around the age of 20. They remain in this state from the age 20 to 35. As middle age approaches the bones - while remaining strong - very gradually begin to lose their density. This loss or thinning of the bones continues as we get older.
The process speeds up in women in the ten years after the menopause. This is because the ovaries stop producing the female sex hormone oestrogen - and oestrogen is one of the substances that helps keep bone strong. Men suffer less from osteoporosis, because their bones are stronger in the first place, and they do not go through the menopause.
All of us are at risk of developing osteoporosis as we get older, which is why elderly people are more likely to break bones when they fall. But there are some people who are more at risk of osteoporosis than others. Several factors can make a difference:
Oestrogen deficiency. Someone who has had an early menopause (before the age of 45), or a hysterectomy where one or both ovaries are removed, is at risk.
Lack of exercise. Exercise keeps bones strong - both as they are developing and throughout adulthood. So anyone who does not exercise, or has an illness that makes it difficult, will be more prone to losing calcium from the bones, and so is more likely to develop osteoporosis.
Poor diet. A diet which does not include enough calcium can encourage osteoporosis.
Heavy smoking. Tobacco lowers the oestrogen level in women and may cause early menopause.
Heavy drinking. A high alcohol intake reduces the ability of the body's cells to make bone.
Steroids. If someone takes prednisolone over a long period of time, it can cause osteoporosis.
Water tablets. Some diuretics may cause the loss of calcium in the urine which could lead to osteoporosis.
Family history. Osteoporosis appears to run in families. This is probably because there is some inherited factor which affects the development of bone.
Previous fractures. People who have already had a fracture are at a greater risk of having another. Men and women who become shorter due to crush fractures of the spine are also more at risk.
There are no obvious physical signs of osteoporosis. It can therefore go unnoticed for years. Quite often the first indication is when a person breaks one of their bones in what might have been normally a minor accident.
If a doctor suspects osteoporosis, he or she can order a bone scan to test the strength or density of the bones. This scan is now available at many hospitals throughout the country. The results will tell how much risk there is of fractures. It takes about fifteen minutes while the bones are X-rayed. The dose of radiation is tiny - about the same as spending a day out in the sun. The technique is called Dual Energy X-ray Apsorptiometry and is known as DEXA.
People with osteoporosis are more likely to break a bone even after a relatively minor injury. Fractures are most likely to the hip, spine of wrist. Hip and wrist fractures are usually sudden and the result of a fall.
Spinal problems occur if - as the vertebrae become weak - they crush together. If several vertebrae are crushed, then the spine will start to curve. This may cause back pain and loss of height, and because there is now less space under the ribs, some people may find difficulty breathing.
Osteoporosis is quite common in Britain. Each year there are around 60,000 hip, 40,000 spine and 50,000 wrist fractures.
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