Rates of change in spinal bone density among Japanese women.

To determine the rates of change in bone mineral density (BMD) at the spine in healthy Japanese women, longitudinal measurements of spinal BMD using dual X-ray absorptiometry were collected from 984 women over 17 years of age (mean age 51.6) at eight medical research centers. They were followed up for 20.9 months on average without any treatment influencing bone and calcium metabolism. Measurements of BMD obtained by two different scanners were converted into standardized BMD (sBMD) values. The multiple linear regression model predicts that spinal sBMD increases up to about 23 years of age: the estimated average rates of increases were 0.13%/year for women aged 20 years. After the age of 23, the sBMD began decreasing: the rates of loss increased by 0.045%/year for each year increase in age among premenopausal women. In perimenopausal women, the rate of loss was 2. 1%/year. In postnatural menopausal women, the rates of loss decreased exponentially with increasing years since menopause. The rates of loss increased by 0.04%/year for 1 kg decrease in body weight or by 0.1%/year for 1 kg/m2 decrease in body mass index. No significant differences in changes in sBMD were found between scanners and between centers after multiple adjustment. We conclude that the rates of change in spinal sBMD are associated with age in premenopausal women, and with years since menopause and weight or BMI in postmenopausal women. Caution is needed, however, when using data from different densitometers to evaluate rates in bone loss in multicenter trials.