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

Objective: To examine the quantity and quality of insomnia symptoms as predictors of treatment for depression in the largest cohort study to date. Methods: Forty 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). Results: One 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. Conclusions: These 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. (C) 2011 Elsevier B.V. All rights reserved.