Reproductive lifespan and cardiovascular health in postmenopausal women: a non-linear, behavior-driven association with cross-population validation - Jie Chen; Jia-yu Shi; Qian Guo; Shi-min Wu; Gu-quan Ma; Xiao-wei Zhao; Yong Tan; Ying-hao Pei (Frontiers in Medicine, 2026)