ABSTRACT
Bone mass Implicit in the definition of osteoporosis by bone mass alone is the notion of a relationship between the amount of bone and fracture risk. Low bone mass is therefore analogous to high blood pressure or an elevated serum cholesterol concentration. The risk of fracture increases when bone mass declines, just as the risk of stroke rises with increasing blood pressure and as hypercholesterolaemia leads to an increased risk of myocardial infarction. Data from an age-stratified random sample of women in Rochester, Minnesota, USA2, were extrapolated to derive the prevalence of osteoporosis in each age group using the WHO definition (see page 28)1. As can be seen in Figure 3.1, most White women under the age of 50 years have normal bone density at all four skeletal sites, and osteoporosis is rare. With advancing age, however, a greater proportion has osteopenia or osteoporosis (Table 3.1). Among women aged 80 years and over, for example, 32% have osteoporosis of the lumbar spine, 47.5% of the hip and 70% at any of the hip, spine or radius. Of the latter group, 60% have experienced one or more fractures of the proximal femur, vertebra, distal forearm, proximal humerus, or pelvis. Overall, an estimated 16.8 million (54%) of postmenopausal white women in the United States have osteopenia and another 9-4 million (30%) have osteoporosis. About 4.8 million women (51% of the osteoporotic women and 16% of all White women age 50 years or above) are estimated to have established osteoporosis, i.e. osteoporosis with fracture3. The latter figure is probably an underestimate since most fractures in elderly women are related at least in part to low bone mass, but only selected fracture sites were considered here. Estimates from other parts of the world are currently being assembled, but hip bone density data from the United Kingdom
suggest that about 23% of women aged 50 years and above have osteoporosis according to the WHO definition1. This proportion would rise considerably if other sites (such as the spine and forearm) were included.
