B A Ochia
Over the past decade osteoporosis has become universally recognised as a major health-care problem in many Western countries, affecting the lives of a large number of individuals. It has been estimated that in the UK alone about 150 000 fractures associated with osteoporosis occur every year. Economically speaking, this has dire financial consequences. In England and Wales estimated costs, relating to clinical consequences of osteoporosis, such as painful fractures which result in increased debility and reduced quality of life, amounted to well over £740 million in 1992. Figures published by Dolan and Torgerson in 1997 showed that in the UK cost of dealing with osteoporosis-related fractures was £942 million, with average costs per fracture of hip, forearm and spine being £12 000, £428 and £479, respectively.
The distinguishing feature of osteoporosis is the occurrence of fractures as a result of little or no trauma in a person whose bone density is reduced. This reduction in bone density (BMD) is scientifically known as osteopaenia. Osteoporosis has been often defined as a systemic bone disease characterised by low bone mass and the deterioration of the fine structure of bone tissue, resulting in increased bone fragility and susceptibility to fracture. With this definition, osteoporosis can only be diagnosed when a fracture has occurred. According to Kamin and Associates, lifetime risks of any osteoporotic fracture for 50-year-old white women and men are 40 and 13%, respectively. A definition proposed in 1994 by the World Health Organisation avoids this by basing osteoporosis on changes in bone mass. So, by knowing the natural history of depletion in bone mass in women as they age, it is possible to predict the incidence of the disease at different ages. For instance, about 15% of women will have osteoporosis at 50 years old, 30% at 70 and 40% at 80. It should be noted that radiological evidence of osteopaenia is not associated with osteoporosis per se. So, the first clinical sign of osteoporosis is the occurrence of fractures.
The three major sites for osteoporotic fractures are the distal radius, the vertebral column and the neck of the femur. It has been estimated by Drs Liggett and Reid in Aberdeen, that in the UK alone 60 000 hip fractures occur annually and, with an ageing population, the value will rise to 90 000 by the year 2005. This figure could be higher if the increasing sedentary lifestyle of the population is taken into account.
Although the risk of osteoporosis is partly related to BMD, trauma also plays an important part. Risk of falling can specifically translate into hip fractures. About 33% of people over 65 years fall annually and about 1% of these falls results in a fracture. Falls in turn are related to instability of posture and reduced muscle power, since patients with low muscle strength are at increased risk of fracture.
Another salient feature of osteoporosis is insufficient production of bone matrix, the basic material from which bone develops, or a serious reduction in bone calcium content. In pronounced osteoporosis, large amounts of calcium are excreted in the urine and may lead to grave kidney complications. This disease is most commonly associated with the post-menopausal state in women, when decreased secretion of the female sex hormone oestrogen changes normal metabolic functions; but it is also attributed to malnutrition and reduced activity. Osteoporosis can therefore be considered primarily as a disorder of tissue metabolism, and only secondarily as a deficiency of calcium and phosphorus.
In osteoporosis, the calcium-hardened mass of all bones decreases because bone resorption, i.e., the normal loss of substance from bone, continues at a regular rate, while bone formation practically ceases. The body responds to this depletion by stimulating bone-generating cell activity so that bone mass is restored to some extent but seldom in sufficient quantity. In the malnutrition often associated with the poor eating habits of the elderly, all protein tissues are depleted; and lack of vitamin C results in reduced production of protoplasm, and this adds to the natural atrophy of bone and other tissues that occurs in older persons. Sometimes over activity of the thyroid gland will cause osteoporosis in younger people, because it increases the rate of metabolism and promotes excessive activity, and that, in turn, places added stress on the bones and increases bone depletion. Osteoporosis very rarely occurs in children; and when it does it is usually attributed to a serious metabolic disorder.
The disease osteoporosis is most common in women over the age of 50. The severity of symptoms has little bearing on the amount of osteoporosis seen on X-ray examination. About 50% of those patients X-rayed will show grossly decreased bone mass, 30% will reveal previously undetected fractures of the vertebrae, but only 10% will have experienced pain or other signs related to these fractures. Artificial or surgically induced menopause usually leads to a more severe degree of bone destruction; however spontaneous fractures of the spine and pelvis are fairly common. Only occasionally are bones of the skull and extremities (arms and legs) affected in osteoporosis. Sometimes the disease causes repeated formation of kidney stones.
It is not known to what extent the bone atrophy that accompanies old age is caused by under function of the sex organs. This under function may be a factor in osteoporosis, since a higher incidence of that disease occurs at an earlier age in women than in men; and men usually experience a climacteric (that group of physical and mental changes associated with decreased sexual activity in old age) much later in life compared to women.
Osteoporosis is influenced by various factors; the first of them is genetic. It has been known for a long time that genetic factors play an important role in the development of osteoporosis. Greater similarities have been found in bone density measurements between identical twins than between non-identical twins. Similarly, daughters of osteoporotic women have lower bone density than have those of matched women of the same age whose mothers have not got osteoporosis. Also bone density is low in relatives of osteroporotic patients. The genes which determine bone mass are very difficult to identify, using classical genetic linkage methods. Recently a vitamin D receptor has been shown to play a role as a genetic determinant of bone mass. Vitamin D, in association with its receptor, is known to play a crucial part in body calcium balance as well as cell differentiation and proliferation in other tissues. The association of vitamin D receptor with BMD is still a controversial subject among scientists.
It is certain that genetic factors are important in determining peak bone mass, a fact that could be important in the regulation of rates of bone loss in perimenopausal women and the elderly. It is hoped that in future one of these factors, or a combination of them, could be used as a predictive test of osteoporotic fractures.
The next factors that affect bone mass are environmental. Calcium intake comes first among them. Calcium supplementation slows down the rate of bone loss in late postmenopausal years, especially in those with average daily calcium intake of 400 mg or less. Studies by C.C. Johnston and co-workers have indicated that calcium intake is also important during bone development. Those scientists gave identical twins, mean age 10 years, 1.6 g calcium each daily for 3 years and found that those given calcium showed increased bone density, compared with controls. Some other workers such as R.B. Sandler and others showed a straight connection between milk intake, during childhood and early adulthood, and BMD in post-menopausal women. However, increased calcium intake has little effect on the rapid bone loss which occurs immediately after menopause.
Mechanical stress is another environmental factor. According to Slemenda and others, there is a positive correlation between physical activity during childhood and bone mass at various skeletal sites. Physical activity and muscle strength are both, in the elderly, related to risk of femoral fractures. Too little or too much exercise is not good for bones. Moderate exercise, such as high-impact weight-bearing activity, can increase bone mass. Smoking and alcohol have negative effects on bone mass, although R.M. Angus and others working in Australia showed that moderate intake of alcohol was associated with increased bone mass.
Exercise intended to be bone-building should be able to increase the load-bearing capacity of the bone. Therefore, the most effective form of exercise is the high-impact weight-bearing activity. This idea is supported by the current enthusiasm for step classes among young women. Even in older women, mean age 65 years, who participated in a 24-month programme of weight-bearing exercise combined with increased dietary calcium intake, there was a significant rise in bone mineral content in the most distal forearm, compared with a control group. The women who exercised fell less often than those who did not, suggesting that the exercise improved their balance, strength and flexibility, thereby reducing the risk of falling down.
Falling is the commonest cause of osteoporotic fractures. The person with disturbed balance and poor leg muscle strength is considerably more prone to fall than are normal individuals. There is now abundant evidence to suggest that exercise programmes directed at improving muscle tone and power can help to reduce the number of falls. For example, the Frailty and Injuries Co-operative Studies conducted in the USA indicated that 10 to 24 weeks of exercise reduced the risk of falling during the following 2 to 4 years. So, prevention of falls appears to be the single most important means of protecting elderly persons against fractures.
Various treatments for osteoporosis are available. There are drugs, such as Etidronate and Bisphosphonates which can be used to prevent bone resorption. These drugs can increase bone mass and reduce the risk of recurrent fractures significantly when given for over 3 years. Etidronate is well tolerated and is free of significant side affects. The use of vitamin D is another recognised mode of treatment. A single daily intake of 800 international units of vitamin D, together with calcium, can considerably reduce hip fractures in elderly patients living in homes. Also supplementary protein, carbohydrate, calcium and vitamins significantly improved outcome in elderly patients with hip fractures. As a secondary preventive for vertebral fractures, Didronel is among the best drugs available. Oestrogen (with or without progestogen) is often the preferred choice for primary prevention. Other treatment agents include calcitonin, fluoride, parathyroid hormone and anabolic steroids; these have been shown to increase bone mass, or prevent bone loss, in various short-term studies. Readers are advised not to resort to these treatments unless as prescribed by their doctors.