Intraindividual variability in sleep among people with insomnia and its relationship with sleep, health and lifestyle factors: an exploratory study

Abstract

Objective: To explore associations between intraindividual variability (IIV) in sleep patterns and sleep problems, lifestyle factors, and mental and physical health in individuals with chronic insomnia. Methods: Cross-sectional study of 1720 adults with chronic insomnia (67.8% female, mean age = 44.5) who completed online self-report questionnaires and kept a sleep diary (for at least 10 out of 14 days). Linear regression analyses examined IIV in sleep patterns as independent variables, and sleep problems, lifestyle factors, and mental and physical health outcomes as dependent variables. Analysis of each sleep variable was separately adjusted for the mean value of the corresponding variable and for selected background factors. Results: IIV in sleep variables was significantly and positively associated with scores on the Insomnia Severity Index (ISI), dysfunctional beliefs and attitudes about sleep (DBAS-16), the Chalder Fatigue Scale (CFQ), body mass index (BMI) and alcohol consumption (AUDIT-C) at study entry. The association between IIV and mental health outcomes (ie the Hospital Anxiety and Depression Scale [HADS] and subjectively reported mental health status [SF-12 Mental health]) were not significant. IIV was associated with higher (ie more positively rated) mean level of sleep quality. Conclusion: IIV of sleep patterns may be a useful construct for understanding subjective experiences of sleep problems, fatigue and health in people with chronic insomnia. Our findings support notions suggesting that IIV offers additional insights beyond those offered by studying mean values alone; however, discordant findings regarding sleep quality highlight the need for further studies to examine the consequences of IIV.