Reproductive lifespan shows an age-specific cardiovascular signal in Chinese women
A longer reproductive lifespan was associated with higher cardiovascular disease risk in younger postmenopausal Chinese women, but the pattern did not extend across the full age range studied. In the CHARLS cohort, the association was nonlinear and appeared to change around a threshold of roughly 31 years of reproductive lifespan among women aged 45 to 55 at baseline. The finding matters because reproductive lifespan is a simple proxy for lifetime estrogen exposure, and estrogen biology is deeply intertwined with vascular function, lipid handling, endothelial health, and arterial inflammation.
The study followed 4,443 women aged 45 years or older who were free of cardiovascular disease at baseline in 2011. Over 7.53 years of follow-up, covering 33,442 person-years, 1,244 women developed incident cardiovascular disease, defined as self-reported physician-diagnosed heart disease or stroke. In that youngest age tertile, the relation between reproductive lifespan and later cardiovascular disease was not linear. Instead, it formed a U-shaped curve with a threshold at about 31 years, identified by two-piecewise Cox regression and supported by a log-likelihood ratio test.
A single threshold does not settle causality, but it does sharpen the clinical question.
Above the 31-year mark in the youngest group, each additional year of reproductive lifespan was associated with higher cardiovascular risk, with a hazard ratio of 1.08 and a 95% confidence interval from 1.03 to 1.13. The P value was 0.003. No comparable thresholds emerged in the older age tertiles, suggesting that age at baseline modified the observed relationship. Sensitivity analyses were described as robust, which strengthens confidence that the pattern was not a statistical artifact of one model choice or one analytic cut point.
Why reproductive lifespan may behave differently in midlife
Reproductive lifespan is calculated as menopause age minus menarche age, so a longer interval usually means a longer duration of endogenous estrogen exposure. In theory, more estrogen exposure should support vascular protection through favorable effects on lipids, nitric oxide signaling, endothelial reactivity, and arterial compliance. Yet biology rarely behaves in a straight line. Prolonged exposure may also track with hormonal patterns, metabolic changes, or reproductive factors that do not reduce to a simple protective story, especially in the years surrounding menopause when cardiometabolic risk begins to rise steeply.
The U-shaped relationship in the youngest postmenopausal women suggests that both shorter and longer reproductive spans may cluster with different cardiovascular risk profiles. Shorter reproductive lifespan can reflect earlier menopause, which has often been linked to adverse cardiometabolic risk. Longer reproductive lifespan in this cohort, however, was associated with higher risk beyond the threshold. One plausible explanation is that reproductive lifespan is acting as a marker for a broader hormonal and metabolic phenotype rather than as a direct causal exposure on its own. Endogenous estrogen exposure may interact with age-related changes in blood pressure, insulin sensitivity, adiposity, inflammation, and vascular remodeling, producing different risk signals depending on when in later life the measurement is made.
The analysis used restricted cubic splines to test nonlinearity, a sensible choice when the clinical question is whether the exposure-risk curve bends rather than marches in a straight line. Cox modeling then allowed the investigators to estimate risk over time while adjusting for follow-up duration. This combination is particularly useful for reproductive epidemiology, where hormonal exposures often have threshold effects, delayed consequences, or age-dependent interactions that standard linear models can miss.
The youngest tertile carried the clearest signal
Age mattered as much as reproductive lifespan itself. In women aged 45 to 55 at baseline, the association became visible and measurable; in older tertiles, the threshold effect disappeared. That age stratification suggests that the cardiovascular meaning of reproductive lifespan depends on the timing of observation, not just on the length of exposure. Midlife may be the period when the biological consequences of reproductive timing are most detectable, before later-life risk is increasingly dominated by accumulated vascular injury, medication use, comorbidity burden, and aging itself.
For clinicians, the immediate implication is not that longer reproductive lifespan should be treated as a standalone cause of cardiovascular disease. The study does not justify using reproductive lifespan in isolation to predict individual risk. It does, however, support the idea that reproductive history can carry clinically relevant information, especially in younger postmenopausal women who may otherwise appear low risk on casual review. Menarche age and menopause age are often asked about for gynecologic reasons; this cohort suggests they may also deserve a place in cardiovascular risk history taking.
A hypothesis-generating result that needs external confirmation
The endpoint was based on self-reported, physician-diagnosed heart disease or stroke, which is a practical definition for a large longitudinal cohort but still leaves room for misclassification. Even so, the consistency of the signal in sensitivity analyses argues that the overall pattern deserves attention. The central limitation is not merely statistical. This is an observational study, so reproductive lifespan may be capturing unmeasured factors tied to socioeconomic status, lifestyle, body composition, menopause timing, or other hormonal variables that were not fully resolved by the analysis presented here.
The cohort was drawn from Chinese women enrolled in CHARLS, so the findings may not translate directly to other populations with different reproductive histories, cardiometabolic patterns, or healthcare access. The study also leaves a practical question unanswered: whether reproductive lifespan adds enough incremental information to improve cardiovascular risk prediction beyond age, blood pressure, diabetes status, smoking history, and body mass index. That question remains open and will require formal validation in independent cohorts before reproductive lifespan can be considered for routine risk stratification.
For now, the clearest message is confined to younger postmenopausal women in this cohort: reproductive lifespan beyond about 31 years was associated with higher subsequent cardiovascular disease risk, while older women did not show the same threshold pattern. The biology is plausible, the curve is non-linear, and the age interaction is real enough to merit follow-up. What is still missing is proof that the metric changes clinical decisions or improves outcomes when added to existing cardiovascular risk assessment.