Policy threshold for decelerating chronic disease accumulation among older Chinese adults: Evidence from the Healthy China 2030 Initiative

Background: Health policy evaluations frequently overlook delayed or cumulative effects due to inadequate observation periods, leading to the premature rejection of beneficial interventions. The optimal duration of policy exposure necessary to achieve measurable health impacts is not well established. This study examines the time-dependent effects of China's Healthy China 2030 (HC2030) initiative on chronic disease accumulation among older adults, utilizing staggered provincial implementation as a natural experiment. Methods: Longitudinal data from 7,487 adults aged 60 years and older in the China Health and Retirement Longitudinal Study (CHARLS, 2011–2018) across 28 provinces were analysed. Staggered HC2030 implementation timing (0–21 month variation) was leveraged within a difference-in-differences framework. Provinces were grouped by exposure duration (short-, medium-, or long-term), and group-specific disease progression trajectories were estimated for each group. Overlap weighting, baseline covariate balancing, and wild cluster bootstrapping were employed to ensure robust inference with a limited number of clusters. Results: Prepolicy placebo tests confirmed the validity of the parallel trends assumption. The policy effects differed by exposure duration: short-term (≤15 months) and medium-term (15–18 months) exposures did not yield significant impacts, whereas divergence in disease progression trajectories emerged at approximately 13 months, indicating stabilization. Long-term exposure (≥19 months) significantly decelerated chronic disease accumulation (β = -0.325, 95% , p = 0.005, WCB), offsetting a substantial portion of the age-related disease burden (population mean increase: 0.45). These results indicate that sustained policy implementation is necessary to achieve meaningful health system benefits. Conclusion: Comprehensive health system reforms require extended implementation periods, with approximately 13 months needed to stabilize disease progression and sustained exposure (≥19 months) necessary to achieve significant cumulative effects (β = -0.325, p = 0.005) before measurable population health benefits are observed. Premature evaluations risk dismissing effective interventions. These threshold estimates provide empirical benchmarks for designing evaluation timelines in chronic disease policy research, particularly in low- and middle-income settings.