Later Menopause Confers No Additional Protection Against Osteoporosis in Older Women

Background: Previous studies may have overestimated the effect of age at menopause when assessing osteoporosis risk and may have overlooked women with late menopause as a high-risk group. Therefore, we aim to clarify the association between age at menopause and osteoporosis risk, as well as to identify key characteristics of individuals with osteoporosis. Methods: This study utilized a nationally representative cross-sectional sample, including 5,804 postmenopausal women aged 55-79 years. Weighted multivariate linear regression and logistic regression models were used to assess the association between age at menopause and femoral neck BMD and osteoporosis. Core characteristics of the osteoporosis population were identified by calculating standardized coefficients and applying SHapley additive interpretation (SHAP) analysis. Restricted cubic spline (RCS) analysis and subgroup analysis were conducted on these core characteristics. Results: The age at menopause showed no significant association with osteoporosis risk in any model (P > 0.05). the two primary modifiable factors associated with reduced osteoporosis risk were BMI(OR = 0.84, 95% CI: 0.80-0.88) and hormone-use history (OR = 0.50, 95% CI: 0.33-0.74). Furthermore, RCS analyses revealed significant nonlinear relationships between age at menopause and both BMI (P < 0.001) and hormone-use history (P < 0.001). Subgroup analyses indicated that the compensatory effects of these two factors varied across different specific subgroups. Conclusion: This study reveals that the initial protective advantage in reducing osteoporosis risk conferred by a later age at menopause diminishes in later life. Maintaining a higher BMI and appropriate hormone therapy can effectively compensate for the initial risk disadvantage.