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 B MD using dual X-ray absorptiometry were collected from 984 women over 17 years of age (mean age 51.6) at eight medical research centers. The y were followed up for 20.9 months on average without any treatment in fluencing bone and calcium metabolism. Measurements of BMD obtained by two different scanners were converted into standardized BMD (sBMD) va lues. The multiple linear regression model predicts that spinal sBMD i ncreases up to about 23 years of age: the estimated average rates of i ncreases 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 perimenop ausal women, the rate of loss was 2.1%/year. In postnatural menopausal women, the rates of loss decreased exponentially with increasing year s 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/m(2) decrease in body mass index. No significant differences in changes in sBMD were found between scanners and between centers after multiple adjustment. We con clude that the rates of change in spinal sBMD are associated with age in premenopausal women, and with years since menopause and weight or B MI in postmenopausal women. Caution is needed, however, when using dat a from different densitometers to evaluate rates in bone loss in multi center trials.