Reproductive span and four-year risk of incident metabolic syndrome among postmenopausal Chinese women: a longitudinal CHARLS study

Previous studies have mainly examined prevalent metabolic syndrome (MetS) and have reported differing directions for reproductive-timing associations; longitudinal evidence among women already postmenopausal is limited. We analyzed the 2011 and 2015 China Health and Retirement Longitudinal Study waves. Reproductive span was calculated from retrospectively recalled ages at menarche and menopause. Among 1,665 women with classifiable MetS status at both waves, 776 were free of MetS in 2011; of these, 188 had MetS in 2015. One woman with missing smoking status was excluded from the adjusted model, leaving 775 women and 187 events. Log-binomial regression with community-cluster-robust inference and marginal standardization estimated risk ratios (RRs) and risk differences (RDs). For a five-year longer reproductive span, the adjusted RR was 1.13 (95% confidence interval [CI], 0.98 to 1.31) and the RD was 3.2 percentage points (95% CI, -0.6 to 7.0). Estimates were similar after adjustment for baseline MetS-component count (RR, 1.11), restriction to women aged 55 years or older (RR, 1.13), and observation-weighted sensitivity analysis (RR, 1.15). The estimate was imprecise and compatible with no association or a modest increase in four-year incident MetS. Substantial outcome non-ascertainment, recalled reproductive timing, uncertain menopause etiology, and residual confounding limit definitive interpretation.