Prevalence and correlates of insomnia in the Swedish population aged 19-75 years.

OBJECTIVE: To assess the prevalence of insomnia symptoms, their associated factors and daytime symptoms in the general population of Sweden.

METHODS: This is a cross-sectional postal survey performed in the general population of Sweden aged between 19 and 75 years (6 million inhabitants). A total of 1209 out of 1705 randomly selected participants from the National Register of the Total Population completed the questionnaire. The participation rate was 71.3%. Participants filled out a paper-pencil questionnaire composed of 157 items covering sociodemographic characteristics, sleeping habits and environment, sleep quality and sleep symptoms, and health status.

RESULTS: We found 32.1% (95% confidence interval: 29.5-34.8%) of the sample reported having difficulty initiating (DIS) or maintaining sleep (DMS) or non-restorative sleep accompanied with sufficient sleep (NRS) at least 4 nights per week: 6.3% of the sample had DIS, 14.5% had DMS and 18.0% had NRS. Results from logistic regressions showed that restless legs symptoms, breathing pauses during sleep and depressive or anxious mood were associated with DIS and DMS but not NRS. Living in an urban area (OR:2.0) and drinking alcohol daily (OR:4.6) were associated only with NRS. Daytime symptoms were reported by over 75% of subjects with insomnia symptoms. DIS, DMS and NRS were associated with daytime fatigue but not excessive sleepiness as measured by the Epworth scale. DIS was associated with the use of sleeping pills or natural sleeping aid compounds in multivariate models.

CONCLUSIONS: Insomnia symptoms occurring at least 4 nights per week are frequent in Sweden, affecting about a third of the population. Subjects with NRS have a distinctly different profile than those with DIS or DMS, which suggests different etiological causes for this symptom.