The association between sleep variability and cognitive function: A systematic review and meta analysis

Sleep variability, also known as sleep irregularity, is an important factor in the physical and mental health of individuals. Numerous previous studies have demonstrated the negative impact of sleep variability on cardiovascular health, metabolic health, and mental health. However, like cardiovascular health, metabolic health, and mental health, cognitive health is a key area of sleep health, but its relationship with sleep variability is still controversial. To uncover the relationship between sleep variability and cognitive health and to explore potential moderators, we conducted a three-level meta-analysis study. By searching three databases, PubMed, Web of Science, and Scopus, we ultimately included 20 published articles including 103 effect sizes (N = 15,828). Analyses showed that higher sleep variability was associated with poorer cognitive performance (r = -0.12, t = -5.13, df = 102, p < 0.001). Age, but not gender or cultural background, significantly moderated this process (F(2,100) = 3.56, p = 0.032). Specifically, the correlation between sleep variability and cognition was significantly lower in adolescents and middle-aged adults compared to older adults. Overall, this study confirms the important impact of sleep variability on cognitive health using meta-analysis and highlights that cognitive health in older adults is more susceptible to impairment by sleep variability, providing guidance for the development of future sleep policies and recommendations as well as the prevention and treatment of dementia in older adults.