Sleep and Cognition at Older Ages and the Moderating Role of Fruit and/or Vegetable Intake: The Empirical Evidence from China

Background: Identifying factors associated with cognitive impairment among older adults is critical. This study investigates both concurrent and longitudinal associations between sleep quality, sleep duration, and cognitive performance among older adults in China, with particular emphasis on the moderating role of fruit and/or vegetable intake (FVI), a factor rarely examined in previous research. Methods: We pooled five waves of a specially designed nationwide sample of adults aged 65 years or older (N = 64,690; mean age: 86.3 years; men: 43.5%) in 2005, 2008, 2011, 2014, and 2018 in China. Cognitive impairment was assessed by the Mini-Mental State Examination. Among the sample, 10.7% were cognitively impaired. FVI was dichotomized into frequent (almost daily) versus infrequent (other low frequencies). Sleep hours were grouped into short (≤6 h), normal (7–9 h), and long (≥10 h) durations. Both concurrent and cross-lagged analyses were performed after adjusting for a wide set of covariates (demographics, socioeconomic status, family/social connections, health practices, disability, self-rated health, and chronic conditions). Analyses were further stratified by gender, age group, and urban–rural residence. Results: When all covariates were present (the full model), good sleep quality was associated with 22% lower odds of the prevalence of cognitive impairment, whereas the long sleep duration was associated with 24% higher odds as compared with the normal sleep duration. Although the short sleep duration was not associated with the prevalence of cognitive impairment in the full model, it was associated with 8% higher odds of cognitive impairment when health condition was not controlled for. Interaction analyses revealed that frequent FVI buffered the adverse cognitive effects of poor sleep quality and both short and long sleep durations. Subgroup analyses further show similar patterns across subpopulations, with more pronounced protective associations in older women and the oldest-old. Conclusions: Good sleep quality, normal sleep durations, and frequent FVI jointly contribute to better cognitive functioning at older ages. While the observed relationships are largely concurrent rather than causal, promoting both healthy sleep and dietary habits may be important for cognitive health among older adults.