Age-related changes in bone mass, structure, and strength--effects of loading.

The incidence of vertebral fracture has increased three- to fourfold for women and more than fourfold for men during the last 30 years. These data are age-adjusted and therefore highlight the decrease in bone mass or bone quality from generation to generation. To arrest or reverse these increases in osteoporotic fractures, effective preventive regimens must be established. However, in order to do so, a basic understanding of age-related changes in the quality and strength of vertebral bone is crucial. In this study, the normal age-related changes in human bone have been investigated by using a combination of different techniques: normal histomorphometry, structural analyses, scanning electron microscopy (SEM), and biomechanical testing. It has been demonstrated that age by itself is the major determinant of vertebral bone strength, mass, and microarchitecture. When the sex-related differences are investigated, three different factors are disclosed: Men have, at the age of 20-30 years, a higher peak bone mass and strength than women. Men show an age-related compensatory increase in bone size (cross-sectional area of the vertebral bodies) which can not be found in women. There is, after the age of 50 years (menopause), a higher tendency for disconnection of the trabecular network in women than in men. Furthermore, it was shown that loading plays an important role in the maintenance of trabecular connectivity (through the remodeling process) and in the periosteal apposition and thereby increase in cross-sectional area (through the modeling process). Loading affects bone mass, microarchitecture, and size throughout life. Loading is therefore important for the maintenance of bone strength during normal aging--and exercise plays an important role in the prevention of osteoporotic fractures.