Age-related bone loss in women evaluated by the single and dual photon technique.

Bone mass and density were measured at two forearm sites (proximal and distal BMC/BMD) and in the spine (spinal BMC/BMD) by respectively single and dual photon absorptiometry in 141 healthy women aged 20-80 years. The proximal forearm site contains approximately 15% trabecular bone and the distal site equal amounts of trabecular and cortical bone. At all three sites linear regression analysis on pre- and postmenopausal women separately revealed accelerated decline in bone density after the menopause. Polynomial regressions in BMC and BMD versus menopause-adjusted age fitted the changes better than a linear regression in the peripheral skeleton, but not in the spine. In both the forearms and the spine the age-related reduction in bone could be described by a combined model, assuming a linear decrease before the menopause and an exponential one thereafter. According to this model, the premenopausal annual changes were 0.067% (proximal site), 0.187% (distal site) and 0.098% (spine). The annual changes during the first postmenopausal year were 3.7, 3.7 and 4.6%. No matter which model was applied to the data, the reduction in the oldest women was lowest in the spine. These data indicate that there are some small differences in the age-related changes in cortical and trabecular bone, but that the reduction of both types of bone accelerates after the menopause.