Insomnia symptoms as a predictor of incident treatment for depression: Prospective cohort study of 40,791 men and women

ObjectiveTo examine the quantity and quality of insomnia symptoms as predictors of treatment for depression in the largest cohort study to date.MethodsForty thousand seven hundred and ninety-one Finnish public sector employees (mean age 43.9 years, 81% female), free of depression at baseline, participated in this prospective observational cohort study. Participants responded to the survey in 2000–2002 or 2004 and the mean follow-up was 3.3 years. Self-reported sleep was linked to comprehensive individual-level health registers to assess treatment for depression (antidepressant medication, commencements of psychotherapy or hospitalization due to depression).ResultsOne thousand seven hundred and three participants fulfilled any of our set criteria for depression-related treatment. After adjustments for baseline characteristics, insomnia symptoms five to seven nights/week were associated with an increased risk of incident treatment for depression, hazard ratio 1.64 (95% confidence interval 1.44–1.86). Hazard ratio for symptoms two to four nights/week was 1.46 (1.29–1.64). Difficulties initiating or maintaining sleep and non-refreshing sleep increased the risk when analyzed separately. Those reporting all four symptoms at least twice a week had 2.09-fold (1.75–2.49) risk. The findings did not materially change after excluding depression cases within the first two years of the follow-up.ConclusionsThese data suggest an association between insomnia symptoms and moderately increased risk of clinically significant depression outcomes. Insomnia should be considered as a component in prediction models for new-onset depression.