Effects of age and menopause on spinal bone mineral density in Japanese women: A ten-year prospective study

In order to determine the age and menopause-related changes in spinal bone mineral density (BMD) in healthy Japanese women, the spinal BMD at L2-4 was measured by dual X-ray absorptiometry (DXA) in 172 healthy Japanese women aged 31-69 years (mean age 53.1 +/- 6.7 years) in 1990 and 2000. This prospective study showed that there was no significant decrease of BMD in premenopausal women, but there was a significant decrease of BMD (-1.59%/year) in the early post menopausal women when compared with the premnenopausal and late postmenopausal women (P < 0.0001). The rate of decrease in BMD slowed down with the prolongation of the years since menopause (YSM). In postmenopausal women the annual rate of decrease in BMD for obese women was significantly lower than that for slim ones (P < 0.01), suggesting that fat tissue may be effective for preventing bone loss. A multiple regression analysis of variables contributing to the annual rate of decrease in spinal BMD showed that YSM and physiological age were the most influential factors, considering other factors such as weight, height and bone mass index. In conclusion, an accelerated bone loss was seen in the early postmenopausal stage. The YSM and physiological age were the most important factors that affect the rate of bone loss in healthy postmenopausal Japanese women.