Sleep duration and cognitive function in middle-aged and older adults: a multinational study in China, England, and India

As the global population ages, the preservation of cognitive function in middle-aged and older adults has become a critical public health issue. Sleep duration represents a modifiable factor associated with cognitive performance, yet its nonlinear relationship across diverse socioeconomic and cultural contexts remains underexplored. This multinational cross-sectional study harmonized data from three representative aging cohorts: the China Health and Retirement Longitudinal Study (CHARLS), the English Longitudinal Study of Ageing (ELSA), and the Longitudinal Aging Study in India (LASI), comprising 25,783 adults aged 50 years or older. Linear regression, piecewise linear models, and random-effects meta-analysis were employed to examine associations between self-reported sleep duration and global cognitive function, adjusting for sociodemographic, lifestyle, and health-related covariates. A consistent inverted U-shaped association was observed between sleep duration and cognitive function across all populations. Both short (≤ 4 h) and long (≥ 9 h) sleep durations were significantly associated with poorer cognitive performance compared to 7 h of sleep (reference). Age and sex significantly moderated this relationship: middle-aged adults (50–64 years) showed greater vulnerability to extreme sleep durations, whereas adults aged 75 years and older were predominantly affected by long sleep. Men were more susceptible to cognitive impairment from short sleep, whereas women exhibited greater sensitivity to long sleep. This study provides the first cross-national evidence of a robust nonlinear sleep-cognition relationship in aging populations across high- and middle-income countries. Our findings suggest that maintaining approximately 7 h of sleep may be optimal for cognitive health in later life. Public health strategies should consider age- and sex-specific interventions to promote healthy sleep patterns and mitigate cognitive decline.