Prefecture-Level Mean Elevation, Sleep Duration, and Depressive Symptoms Among Middle-Aged and Older Adults in China: A Cross-Sectional CHARLS Study

Background: Prefecture-level mean elevation, as an area-level proxy of residential altitude, has been associated with sleep disturbance and depressive symptoms, but it may also reflect broader regional differences in social conditions. The roles of sleep duration and regional context remain uncertain among long-term community residents. Objectives: To examine these associations among adults aged 45 years or older in China. Methods: This cross-sectional study linked nationally representative China Health and Retirement Longitudinal Study Wave 4 data from 15,562 adults aged 45 years or older with prefecture-level mean elevation. Linear regression with province fixed effects assessed sleep duration and CESD-10 scores. Altitude-by-sleep interactions, generalized additive models, restricted cubic splines, and exploratory bootstrap mediation analyses were conducted. Results: Moderate and high altitude were associated with higher CESD-10 scores in unadjusted models, but not after adjustment for sleep category, individual covariates, and province fixed effects. They were associated with 0.280 and 0.363 h longer self-reported sleep. The altitude-by-sleep interaction was significant, and predicted CESD-10 scores were highest among short sleepers across altitude groups. Nonlinear patterns were observed, whereas indirect effects through continuous sleep duration were not significant. Conclusions: The apparent association between higher altitude and depressive symptoms was not robust after regional adjustment. Sleep duration did not show evidence of mediation, although sleep category was associated with differences in the observed altitude–depressive symptom pattern.