Nonlinear association between self-reported sleep duration and cognitive function among middle-aged and older adults in China: The moderating effect of informal care

Background: Cognitive impairment is a major public health problem urgently to be solved. This study aims to examine the association between sleep duration and cognitive function and its two subdimensions: episodic memory and mental status, and to explore the moderating effects of informal care on these associations among middle-aged and older adults in China.

Methods: Data was drawn from China Health and Retirement Longitudinal Study (CHARLS) 2011, 2013, 2015 and 2018 datasets. Sleep duration and informal care were self-reported. Cognitive function was measured using CHARLS Harmonized Cognitive Assessment Protocol. Effects of informal care on sleep duration-cognitive function were assessed using Generalized Estimating Equations models. 

Results: The relationships between sleep duration and cognitive function, episodic memory, and mental status were all found to follow an inverted U-shaped pattern. Spouse care weakened the adverse effects of extreme sleep duration on cognitive function while the children care amplified them. Further, we only observed the moderating effects of spouse and children care on the association between sleep duration and episodic memory, but not mental status.

Conclusions: The relationships between sleep duration and cognitive function, along with its different dimensions, are nonlinear in nature. The impacts of sleep duration on cognitive function and its dimensions are contingent upon the levels of informal care received and the sources of that care. We provide valuable insights into the complex interplay between sleep duration, informal care, and cognitive function.