Pre- and postmenopausal bone mineral density of the spine and proximal femur in Japanese women assessed by dual-energy x-ray absorptiometry: a cross-sectional study.

To investigate the influence of menopause on bone mineral density (BMD) of Japanese women, BMD of the spine and proximal femur was measured by dual-energy x-ray absorptiometry (DXA) in 220 premenopausal and 166 postmenopausal Japanese women. The peak bone density of the spine in premenopausal women was detected between 35 and 39 years of age, and that of femur before 20. Thereafter spinal and femoral BMD showed a slight decrease, but they did not show a significant decrease until menopause or menstruation became irregular. Duration of substantial bone loss at lumbar spine continued for about 10 years after menopause, but that at the femur was much longer. To investigate the effect of early menopause on bone loss, postmenopausal women were divided into two groups according to the age at onset of menopause. The BMD of postmenopausal women whose menopause occurred before 50 was significantly less over the latter part of life than that of women whose menopause occurred after 50. These results suggest that bone loss is related to menopause or irregular menstruation rather than age per se, and early menopause should be recognized as one of the risk factors for involutional osteoporosis.