Prospective study of predictors and consequences of insomnia: personality, lifestyle, mental health, and work-related stressors.

Objective: To prospectively investigate the reciprocal relationships between personality traits, lifestyle factors, mental health, sleepiness, and work-related stressors against insomnia.
Methods: A total of 799 Norwegian shift-working nurses (mean age 33.2 years, 90% female) participated in this prospective cohort study. They were assessed on self-report instruments (Bergen Insomnia Scale, Diurnal Type Scale, Hospital Anxiety and Depression Scale, Negative Acts Questionnaire-Revised, Work-Family Interface Scale, among others) in 2008/2009 (wave 1) and 2011 (wave 3). Structural equation modeling was employed to investigate the bidirectional relationship between a wide range of individual and work-related variables and insomnia.
Results: Languidity (β = 0.18***), anxiety (β = 0.11**), depression (β = 0.14***), exposure to bullying behavior (β = 0.08*), and negative spillover between work and family life (work to family, β = 0.08*; family to work, β = 0.07*) predicted increased symptoms of insomnia over time. Morningness (β = -0.09*) and positive spillover from work to family (β = -0.11**) predicted less symptoms of insomnia over time. No support was found for night work as a predictor of increased insomnia. Insomnia was a precursor for anxiety (β = 0.11**), but not for depression (*p <0.05, **p <0.01, ***p <0.001).
Conclusion: The data suggested that insomnia more often emerges as a consequence of individual and work-related factors than as a precursor to them. The scope of factors causing insomnia, and factors protecting against it, should be further investigated. Insomnia should be considered in prediction models for mental illnesses and as an outcome of adverse work-related experiences.
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