What changes in bone health occur with aging?
Prospective data indicate that peak bone mass occurs during late teenage years in women and about a decade later in men. Because of intimate structural and functional links between muscle and bone, the occurrence of peak bone mass likely corresponds with peak skeletal muscle development. It is generally thought that bone mass is maintained, or decreases slowly (< 0.2% per year), at least through age 40 years in women and age 50 years in men. Intuitively, a decline in physical activity during middle age might be expected to induce an even faster rate of bone loss. However, the increase in body weight that typically also occurs during middle age may counter this to a large extent by increasing mechanical loading forces acting on the skeleton during weight-bearing activity. There is an inevitable loss of bone mass in older age that increases the risk for osteoporosis in elderly men and augments the risk for osteoporosis in postmenopausal women. In elderly women and men, the decrease in bone mineral density (BMD) at the hip appears to be accelerated (∼1% per year) relative to changes at the spine. In fact, spine BMD may seem to increase in advanced age, when vertebral compression fractures and the development of extravertebral osteophytes lead to an apparent increase in BMD that does not actually reflect increased vertebral bone strength. The utility of measuring spine BMD for the diagnosis of osteoporosis in the elderly can, therefore, be compromised.
In addition to bone density, bone quality is an important component of overall bone strength and changes in bone quality can also increase the risk for an osteoporotic fracture. Bone quality properties include porosity, architecture and geometry, turnover, damage, and mineral content. Higher resolution imaging techniques suggest that overall bone quality declines with age because of factors such as increased cortical and trabecular porosity and decreased volumetric BMD. These changes are not captured by standard dual-energy x-ray absorptiometry (DXA) screening.