Objective: Evaluate the association between years since menopause and bone mineral density (BMD), and to identify the time point at which the slope of the association between BMD and years since menopause changes in postmenopausal women.
Subjects and Methods: A retrospective cross-sectional study based on DXA and medical records was conducted among 13,915postmenopausal women who underwent bone mineral density assessment at Hanoi Medical University Hospital between 2018 and 2025.
Results: T-scores and BMD at all skeletal sites declined significantly with increasing years since menopause (all p < 0.001). Pearson correlation coefficients between T-score and years since menopause were strongest at the femoral neck (r = -0.498 to -0.499) and weaker at the lumbar spine (r = -0.293 to -0.365).. Piecewise regression identified a change point in the rate of bone loss occurring 10-14 years after menopause, with 5 of the 7 skeletal sites showing a breakpoint at 10 years. Beyond this point, the rate of BMD decline at the lumbar spine decreased to 25-31% of the pre-breakpoint rate, whereas the femoral neck maintained approximately 50-58% of its earlier rate of decline.
Conclusions: BMD was significantly lower among women with longer time since menopause at all measured sites, with the strongest association at the femoral neck, and the slope of this association changed approximately 10 years after menopause. Years since menopause may provide supportive information for osteoporosis risk assessment, while decisions on DXA referral and treatment should remain based on age, fracture risk factors, BMD/FRAX and clinical guidelines..