Dietary Patterns and Their Association with Cognitive Function: A Stratified Analysis by Sleep Duration in Japanese Older Adults

Background/Objective: This study investigated the associations between dietary patterns and cognitive function among older Japanese adults and examined whether these associations differed according to sleep duration. Methods: This longitudinal cohort study was conducted using data from the Community Empowerment and Care study (2017–2020). Data were obtained from the Community Empowerment and Care Study of the T-Village, Aichi Prefecture, Japan. Latent class analysis was used to identify dietary patterns based on the intake frequencies of seven food groups. Logistic regression models assessed the associations between dietary patterns and cognitive function stratified by sleep duration (optimal: 7–8 h; unfavorable: <7 or >8 h). Results: The following three dietary patterns were identified: diverse, balanced, and restricted. Diverse (odds ratio [OR], 0.44) and balanced (OR, 0.39) diets were associated with lower odds of cognitive decline. Stratified analysis revealed stronger protective effects of these diets in those with unfavorable sleep. Conclusion: Dietary quality plays a key role in cognitive health and may be particularly beneficial for older adults with suboptimal sleep durations. The study findings underscore the need for integrated lifestyle interventions that target both nutrition and sleep in aging populations.