Examining the Bidirectional Relationship Between Sleep Disorders and Mental Health Across the Life Span in Nigeria: A Multi-Cohort Panel Study

The bidirectional relationship between sleep disorders and mental health outcomes is well-established in Western epidemiological literature, yet no multi-cohort longitudinal study has examined this bidirectionality across different life stages in Nigeria, where unique social, environmental, and cultural factors shape both sleep behaviour and mental health. This study examines bidirectional relationships between sleep disorders and mental health across adolescent, adult, and older adult cohorts in Nigeria through a multi-cohort panel design. Three independent cohorts of 300 participants each (adolescents 13 to 18, adults 25 to 50, older adults 60 and above) are recruited from Enugu State, Sokoto State, and Niger State respectively, each surveyed at three time points with 12-month intervals. The Pittsburgh Sleep Quality Index, the Insomnia Severity Index, the PHQ-9, and GAD-7 are administered at each wave alongside objective actigraphy in a sub-sample of 60 per cohort. Cross-lagged panel models and latent growth curve analysis in Mplus examine bidirectional temporal effects across life stages. Riemann's Cognitive Model of Insomnia, the Two-Process Model of Sleep Regulation, and Life Span Developmental Psychology Theory provide the theoretical framework. The original contribution is the first multi-cohort longitudinal study of sleep-mental health bidirectionality in Nigeria, providing age-differentiated evidence with direct implications for sleep and mental health intervention design across the Nigerian life span. Keywords: sleep disorders, mental health, bidirectional relationship, multi-cohort, Nigeria.