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 subjective 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 subjective cognitive function stratified by sleep duration (optimal: 7–8 h; unfavorable: <7 or >8 h). Results: Three dietary patterns were identified (diverse, balanced, restricted). Compared with the restricted pattern, the diverse (odds ratio = 0.13, 95% confidence interval: 0.07–0.26; p < 0.0001) and balanced patterns (odds ratio = 0.33, 95% confidence interval: 0.18–0.62; p = 0.0006) were associated with lower odds of poor subjective cognitive function. Associations were broadly similar across sleep groups, and interaction testing was not significant. Conclusions: Dietary quality was associated with better subjective cognitive function, particularly among older adults with unfavorable sleep duration. The study findings underscore the need for integrated lifestyle interventions that target both nutrition and sleep in aging populations.