Study objective: To study prospectively the relations of insomnia to the development of anxiety disorders and depression in a population-based sample.
Design: Cohort study based on data from 2 general health surveys of the adult population.
Setting: Two general health surveys in the adult population in Nord-Trøndelag County of Norway, HUNT-1 performed in 1984-6 and HUNT-2 in 1995-7
Participants: Participants without significant anxiety and depression in HUNT-1 were categorized according to the presence and absence of insomnia in the 2 surveys (N=25,130).
Measurements and results: Anxiety disorders and depression in HUNT-2 were assessed by the Hospital Anxiety and Depression Scale and analyzed using multivariate logistic regression analysis adjusted for age, gender, education, comorbid depression/anxiety, and history of insomnia. Anxiety disorders in HUNT-2 were significantly associated with the group with insomnia in HUNT-1 only (OR 1.6; 95% CI, 1.1-2.3), the group with insomnia in HUNT-2 only (OR 3.4; 95% CI, 3.1-3.8), as well as with the group with insomnia in both surveys (OR 4.9; 95% CI, 3.8-6.4). Depression in HUNT-2 was significantly associated with the group with insomnia in HUNT-2 only (OR 1.8; 95% CI, 1.6-2.0), but not with the groups with insomnia in HUNT-1 only or with insomnia in both surveys.
Conclusions: Only a state-like association between insomnia and depression was found. In addition to being a state marker, insomnia may be a trait marker for individuals at risk for developing anxiety disorders. Results are consistent with insomnia being a risk factor for the development of anxiety disorders.