Sleep duration, depression, and cognitive function among older adults in China: A longitudinal cohort study

OBJECTIVE: To explore interactions between depression and sleep duration and their impact on long-term cognitive trajectories. METHODS: This longitudinal study (2011-2020) analyzed depressive symptoms and sleep duration in relation to 10-year cognitive trajectories in 7649 Chinese adults aged 45-80 years. Exposures included sleep duration and depressive symptoms. Cognitive function was the primary outcome, standardized using regression models adjusted for age, sex, and education. Standardized Z-scores for global cognition, episodic memory, and mental status were derived. Growth mixture modeling identified three cognitive trajectories. Multivariable logistic regression examined exposure-trajectory associations. RESULTS: Three distinct cognitive trajectories were identified: persistently high, moderately stable, and persistently low. Compared with the "non-depression-optimal sleep" group, all other sleep-depression groups showed significantly reduced associations, with "depression-long sleep" exhibiting the highest risk of low cognition. Within the persistent moderate group, all combinations except "non-depression-short sleep" showed significant negative associations, with "depression-long sleep" exhibiting the greatest risk. Sleep duration had a U-shaped relationship with cognitive scores, whereas depressive symptoms were negatively associated. Optimal cognitive maintenance occurred among participants with no depression and a 6-8 h sleep duration. CONCLUSIONS: Promoting regular, healthy sleep and reducing depression risk may help preserve cognitive function in old age.