Irregular sleep is linked to poorer mental health: A pooled analysis of eight studies

Objectives: Greater sleep disturbances on average are a risk factor for impaired mental health. Recent research has shown that more intraindividual variability (i.e., inconsistency) in sleep (hereafter called “sleep intraindividual variability”) may also be uniquely related to mental health, even above the influence of mean sleep patterns averaged across days. The current study examined associations between sleep intraindividual variability and symptoms of anxiety, depression, and insomnia across different facets of sleep intraindividual variability (sleep duration, efficiency, and timing) and sleep measurement types (sleep diary and actigraphy). Methods: We pooled eight datasets (N = 3053 participants) that assessed repeated measures of sleep diary- and/or actigraphy-determined sleep across multiple days, as well as one-time measures of mental health or sleep disorder symptoms (i.e., anxiety, depression, and insomnia). Multilevel regression analyses were conducted to examine associations between sleep intraindividual variability and mental health or sleep disorder symptoms. Results: Greater diary- and actigraphy-determined sleep duration intraindividual variability was associated with more depression symptoms (diary: b = 0.02, p < .001; actigraphy: b = 0.03, p = .006) and more insomnia symptoms (diary: b = 0.02, p < .001; actigraphy: b = 0.02, p < .001). Greater diary-determined sleep efficiency intraindividual variability was associated with fewer anxiety symptoms (b = − 0.23, p = .019) and fewer insomnia symptoms (b = − 0.15, p < .001). Greater diary- and actigraphy-determined sleep midpoint intraindividual variability was associated with more insomnia symptoms (diary: b = 0.41, p = .044; actigraphy: b = 0.66, p = .021). Conclusions: More inconsistent sleep duration and sleep timing may be a correlate of poorer mental health. Future experimental work should examine whether stabilizing sleep patterns can improve mental health outcomes.