Association of Reproductive Factors with Osteoarthritis and the Mediating Effect of Body Mass Index Among Postmenopausal Women.

Osteoarthritis (OA) is the leading cause of disability worldwide, with a higher prevalence and severity of functional impairment observed in women over the age of 50. However, the reasons for this gender disparity are not well understood. This study aims to investigate the potential association between reproductive factors and OA prevalence in postmenopausal women, as well as whether body mass index (BMI) mediates this relationship. Public data from 6,066 postmenopausal women collected by the National Health and Nutrition Examination Survey from 1999 to 2018 were used for the analysis. Weighted multivariable logistic regression assessed the association between reproductive factors and OA prevalence, with restricted cubic splines (RCS) analyzing nonlinear associations, and mediation analysis examining BMI's mediating role. RCS models revealed a W-shaped relationship between OA risk and age at menopause, a U-shaped relationship with age at first birth, and an inverted W-shaped relationship with age at last birth. Weighted multivariable logistic regression showed that postmenopausal women with bilateral oophorectomy (odds ratio [OR] = 1.29), exogenous hormone use (OR = 1.44), or a history of breastfeeding (OR = 1.31) had a higher risk of OA, while a later age at menarche was significantly associated with a lower risk (OR = 0.93). Mediation analysis indicated that BMI mediated 34.53% of the association between age at menarche and OA and 18.39% between bilateral oophorectomy and OA. Multiple reproductive factors are independent risk factors for OA. Early surveillance and preventive interventions for OA might be strengthened in high-risk populations with specific reproductive characteristics.