Moderating effects of age-friendly neighborhood on the impact of multimorbidity trajectories on functional decline and depressive symptoms in middle-aged and older Chinese adults: a longitudinal study

Multimorbidity accelerates functional decline and worsens depressive symptoms in aging populations, yet it remains unclear how the dynamic accumulation of chronic conditions affects health deterioration over time and whether supportive neighborhood environments can buffer these effects. Using data from 10,043 Chinese adults aged ≥ 45 years across five waves (2011–2020) of the China Health and Retirement Longitudinal Study, we identified three distinct multimorbidity trajectories via group-based trajectory modeling: no multimorbidity (11.9%), moderate increase (57.1%), and rapid increase (31.0%). Latent growth curve models showed that faster multimorbidity progression was associated with accelerated functional decline (β = 0.050) and worsening depressive symptoms (β = 0.191). However, favorable neighborhood environments—particularly transportation infrastructure, housing quality, and government support—significantly buffered these adverse effects. Improved transportation slowed disability progression (β=-0.057) and depressive symptom increase (β=-0.183); better housing linked to lower baseline depression (β=-0.322); and government support reduced functional impairment (β=-0.179). These findings highlight that age-friendly neighborhood design can mitigate the cumulative negative health impacts of multimorbidity, offering promising community-level intervention targets such as enhancing transport accessibility, improving housing, and strengthening social participation facilities.