osteoporosis

A group of diseases characterized by a reduction in bone mass due to bone reabsorption outpacing bone deposition. The disease is usually associated with loss of weight. Other symptoms include feelings of lassitude, bone pains, and acute back pain. However, the most harmful effect of the disease is that bone becomes porous, brittle, and inclined to fracture. Over 250 000 Americans, most of them elderly, fall and break their hips each year, resulting in a $10 billion medical bill. Worldwide, the disease affects 1.7 million people each year. The number is expected to grow to over 6 million a year by 2050. A quarter of these people are expected to die within six months because of complications, usually linked to hip fractures.

Osteoporosis is an age-related disease, primarily affecting post-menopausal women, although it can occur much earlier in life (figure 47). There is always some degree of bone weakening with age, but insufficient exercise and a low calcium diet (especially in early life) may exacerbate this. Excessive exercising and weight-loss dieting are also linked with development of the disease. Development of the disease may be determined to some extent by a single gene. A gene affecting Vitamin D metabolism has been found in Australians which may be responsible for more than 75 per cent of the genetic variation in their bone density. If this gene occurs in a broader population, it may not be long before genetic screening can be used to identify those who are predisposed to the disease, so that preventative measures can be taken.
Physical exercise reduces the risk of osteoporosis. Moderate weight-bearing exercises, such as leisurely cycling, dancing, walking, and tennis, stimulate the deposition of calcium, strengthen bones, and reduce the risk of osteoporosis. However, young people benefit most from exercise; strong and healthy bones are more easily established in adolescents and young adults. A modest amount of jumping (as little as 50 jumps a day) can increase the density of hips in premenopausal women by as much as 3 per cent. Although exercise may offer some protection against acquiring the disease, those already suffering from osteoporosis should avoid contact sports and exercise that put undue stress on bones and joints. In particular, flexion exercises of the spine (e.g. sit ups) should be avoided because of the risk of vertebral fractures. Swimming is an especially good exercise for those with the disease.

Slightly overweight post-menopausal women are less likely to suffer from brittle bones than slim women. Possible reasons are that fat acts as a protective cushion; bones of plump women may be heavier and stronger; and the extra fat of plumper women enables them to produce more oestrogen which offers some protection against demineralization of bones.

A diet that includes a good intake of calcium-rich food (e.g. milk, yogurt, and cheese) may help prevent and minimize problems associated with this disease. It appears that it is particularly important for pre-menopausal women to have adequate calcium intakes so that they can achieve maximum peak bone densities. At present, the UK Reference Nutrient Intake is thought by The National Osteoporosis Society (UK) to be too low. They recommend the following calcium intakes:
• children 7-12 years 800 mg per day
• teenagers/adults 1000 mg per day
• women over 45 (not on HRT) 1500 mg per day
• women over 45 (on HRT) 1000 mg per day
• pregnant and lactating teenagers 1500 mg per day
• pregnant and lactating adults 1200 mg per day
• men over 45 years 1500 mg per day


Some doctors believe that the best way to prevent osteoporosis in post-menopausal women is hormone replacement therapy (see menopause), but this treatment is not suitable for all women. See also amenorrhoea and parathyroid hormone.
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