Incidence and risk factors of insomnia in a population-based sample.

INTRODUCTION: Despite the high prevalence of insomnia, there is little information about its incidence and risk factors. This study estimated the incidence of insomnia and examined potential risk factors in a cohort of good sleepers followed over a one-year period.

METHODS: Participants were 464 good sleepers who completed 3 postal evaluations over a one-year period (i.e., baseline, 6 months, and 12 months). Questionnaires assessed sleep, psychological and personality variables, stressful life events and coping skills, and health-related quality of life. Participants were categorized into 3 subgroups: (a) good sleepers (i.e., participants who remained good sleepers at the 3 assessments), (b) insomnia symptoms incident cases (i.e., developed insomnia symptoms either at 6- or 12-month follow-up), and (c) insomnia syndrome incident cases (i.e., developed an insomnia syndrome either at 6- or 12- month follow-up).

RESULTS: One-year incidence rates were 30.7% for insomnia symptoms and 7.4% for insomnia syndrome. These rates decreased to 28.8% and 3.9% for those without prior lifetime episode of insomnia. Compared to good sleepers and insomnia symptoms incident cases, insomnia syndrome incident cases presented a premorbid psychological vulnerability to insomnia, characterized by higher depressive and anxiety symptoms, lower extraversion, higher arousability, and poorer self-rated mental health at baseline. They also presented a higher level of bodily pain and a poorer general health. Five variables were associated with a new onset of an insomnia syndrome: previous episode of insomnia, positive family history of insomnia, higher arousability predisposition, poorer self-rated general health, and higher bodily pain.

CONCLUSION: The one-year insomnia incidence rate was very high and several psychological and health factors were associated with new onset insomnia. Improved knowledge about the nature of these predisposing factors would be helpful to guide the development of effective public health prevention and intervention programs to promote better sleep quality.