Association of educational attainment with incident orientation impairment among Chinese older adults with and without stroke: evidence from a longitudinal study with external validation

Background Orientation impairment is an early and clinically meaningful marker of cognitive vulnerability in older adults and is associated with subsequent functional decline, dementia, and mortality. Although stroke is a well-established risk factor for late-life cognitive impairment, its association with incident orientation impairment in community-dwelling populations remains unclear. Educational attainment, a key indicator of cognitive reserve, may modify the cognitive consequences of stroke, but longitudinal evidence addressing this hypothesis is limited. Methods We conducted a population-based longitudinal study using data from the China Health and Retirement Longitudinal Study (CHARLS). Participants aged ≥ 60 years who were free of orientation impairment at baseline (2018) were followed for incident orientation impairment in 2020. Stroke history was defined by self-reported physician diagnosis at baseline. Educational attainment was primarily modeled as a continuous variable (per three-year increase) and additionally evaluated using categorical specifications in sensitivity analyses. Modified Poisson regression with robust variance estimation was used to estimate relative risks (RRs). Effect modification by education was assessed using interaction terms and marginal effect estimation. Sensitivity analyses included inverse probability weighting for loss to follow-up, competing-risk models accounting for death, alternative outcome definitions, and complementary machine-learning analyses. External validation was conducted to examine the transportability of relative risk patterns rather than to formally validate a clinical prediction model. Results Among 9,080 participants free of orientation impairment at baseline, 5,289 participants with observed follow-up orientation assessments were included (complete-case with respect to the outcome), of whom 744 developed incident orientation impairment over two years. Stroke history was not independently associated with incident orientation impairment after multivariable adjustment (RR 0.88, 95% CI 0.63–1.24). In contrast, higher educational attainment showed a strong and consistent protective association: each additional three years of education was associated with a 25.6% lower risk of incident orientation impairment (RR 0.74, 95% CI 0.65–0.86). Formal tests for stroke–education interaction were not statistically significant on multiplicative or additive scales; however, marginal estimates were directionally consistent with attenuation of stroke-associated risk at higher education levels, but estimates were imprecise and confidence intervals crossed the null. Results were robust across sensitivity analyses. Machine-learning models demonstrated modest discrimination and did not materially outperform traditional regression models. External validation showed moderate discrimination but indicated miscalibration of absolute risk estimates, suggesting the need for recalibration in different population settings. Conclusions In this nationally representative cohort of older adults, educational attainment emerged as a consistent and robust protective factor against incident orientation impairment, whereas stroke history showed no independent association after adjustment. Evidence for education modifying the stroke–orientation relationship was suggestive but inconclusive. These findings highlight the central role of educational gradients in late-life cognitive vulnerability and underscore the challenges of detecting domain-specific cognitive consequences of stroke in population-based studies.