The condition involves a net loss of bone density and disruption of bone architecture and is sometimes confused with osteoarthritis which is a problem of the joints – the cartilage and surrounding soft tissues. The diagnosis of osteoporosis is made by special X-ray techniques which measure the mineral density of bone.
Osteoporosis mainly affects a type of bone known as trabecular bone because it has a mesh-like architecture. X-rays of affected bone show many perforations which weaken the structure.
Bone Turnover
Bone like every other tissue in the body is constantly being broken down and replaced. The major mineral in bone which gives it its hardness is calcium. Specialised cells called osteoclasts breakdown bone and release calcium into the blood. Other cells called osteoblasts do the opposite and build up bone.
This breakdown and build up is intimately related to various hormone levels – and therefore age - diet and exercise as well as general health. Bones continue to strengthen throughout early life and reach a peak in the early twenties. Around age forty bone density starts to decrease in both women and men and this continues to the end of life. After the menopause there is sudden acceleration in bone density reduction, this then slows to that of normal after the menopause.
People who have greater bone density to start with are less likely to suffer from osteoporosis, men are less susceptible than women partly because they start with greater bone density. As people live longer the incidence of osteoporosis will increase although there is some evidence that the problem is growing at a greater rate than would be predicted by the growing number of elderly, this may be linked sedentary life-style.
Consequences of Osteoporosis
Fracture and bone collapse are the biggest problems. It is estimated that around 300,000 fractures a year in the UK are due to osteoporosis. The weakened bones can break from mild trauma and spontaneous fractures can also occur. Frequent sites are the upper femur, the wrist and the vertebrae. The vertebrae can collapse which may lead to spinal deformity and nerve root entrapment.
As some elderly people are unsteady and liable to falls the likelihood of serious fractures is considerable. All this adds up to osteoporosis being a major cause of illness and disability.
Risk Factors for Osteoporosis
Although age and menopause are major risks numerous other factors can influence the quality of bone.
- Age: osteoporosis becomes increasingly common in those over 50 years.
- Female: women, for the reasons stated are six times more likely to be affected than men.
- Hormone dysfunction: various hormone problems will leave some at risk – these include hyperthyroidism, hyperparathryroidism, Cushing's syndrome and sex hormone dysfunction which causes a reduction in sex hormones at an early age.
- Poor diet: this is especially so if deficient in calcium and vitamin D. Anorexia nervosa is a risk factor since adequate diet when young, as the bones are maturing, is vital.
- Malabsorption diseases: anything that inhibits the proper uptake of calcium and vitamin will pose a risk.
- Being underweight.
- Hereditary.
- Lack of exercise: bones tend to de-mineralise if the muscles attached to them are not used sufficiently frequently. Exercise in early life is considered important for the proper development of bone.
- Medication: certain drugs can increase the risk of osteoporosis – prolonged use of steroid medication is the most common.
Prevention and Management of Osteoporosis.
Preventative measures are normally instituted in people thought to be at greatest risk such as those who are very thin, those with a family history of osteoporosis and women who have an early menopause.
- Hormone replacement therapy: slows down hormone related bone mineral loss and can therefore be used to prevent osteoporosis.
- Treatment of underlying cause if there is one.
- Prevention of falls: this may mean adapting living areas and reduction in sedatives.
- Adequate intake of vitamin D and calcium; diet and supplementation.
- Increase physical exercise.
- Medication; bisphosphonates are the most frequently used drugs, they work by slowing down bone turnover.
Resources
National Osteoporosis Society.
Human Anatomy and Physiology by Carola, Harley and Noback. Pub. McGraw Hill 1992
ABC of Rheumatology Ed. M. Snaith Pub. BMJ Publishing 2004
British National Formulary 2004 BMA publishing
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