AGE-RELATED BONE CHANGES

Bone changes occur during normal aging in both men and women. Changes are both quantitative and qualitative in nature, and include: 1) alterations in the dynamics of bone cell populations, resulting in uncoupling of the normal process of bone resorption and formation; 2) changes in bone architecture (e.g., rearrangement of trabecular struts) and cross-sectional geometry (characterized by subperiosteal expansion and enlargement of the medullary cavity); 3) accumulation of microfractures; 4) localized disparity in the concentration of deposited minerals, with hypomineralization in some areas and hypermineralization in others; 5) changes in the crystalline properties of mineral deposits; and 6) changes in the protein content of matrix material. In addition, there are age-related changes in the status of calcium and phosphate regulating hormones: parathyroid hormone increases, and production of the most active metabolites of vitamin D3 decreases. These hormonal changes undoubtedly affect the maintenance of normal bone homeostasis. Other important factors which can profoundly influence bone status in the elderly are decreased physical activity and dietary inadequacies. Bone tissue is particularly responsive to mechanical loading, and the magnitude of bone mass loss as a consequence of decreased physical activity may not be fully appreciated. Interactions of the above mentioned changes are not completely understood, and the degree to which these changes have been documented in humans varies considerably. Clearly, however, the overall net result is the occurrence of age-related loss of bone tissue and bone strength. This process is accelerated after menopause in women, resulting in the clinical condition commonly known as osteoporosis. In addition to loss of bone mass (usually reported as a decrease in bone mineral content), osteoporosis is accompanied by bone pain, spinal deformity, loss of height, and fractures.