Prevalence and associated factors of DSM-V insomnia in Norway: the Nord-Trøndelag Health Study (HUNT 3).

Background: Many studies have assessed the prevalence of insomnia, but the influence of non-participants has largely been ignored. The objective of the present study was to estimate the prevalence and associated factors of insomnia in a large adult population using DSM-V (diagnostic and statistical manual of mental disorders, 5th ed.) criteria, also taking non-participants into account.

Methods: This cross-sectional study used data from a questionnaire in The Nord-Trøndelag Health Study (HUNT 3) performed in 2006-2008, and a subsequent non-participant study. The total adult population (n=93,860 aged > or =20 years) of Nord-Trøndelag County, Norway, was invited. Of these, 40,535 responded to the insomnia questionnaire. Among 42,024 eligible non-participants, 6918 (17%) responded to two insomnia questions.

Results: Insomnia was diagnosed by applying modified DSM-V criteria. The age-adjusted insomnia prevalence was estimated using the age distribution of all adult inhabitants of Nord-Trøndelag. Supplementary prevalence data were estimated by extrapolating data from the non-participant study. Additionally, the association between insomnia and self-reported health was estimated, adjusting for known confounders. The total age-adjusted prevalence of insomnia was 7.1% (95% confidence interval [CI], 6.9-7.4) (8.6% for women, 5.5% for men). Adjusting for non-participants, the prevalence estimate changed to 7.9% (95% CI, 7.3-8.6) (9.4% for women, 6.4% for men). Insomnia was more than eight times more likely (OR, 8.3; 95% CI, 6.2-11.1) among individuals with very poor versus very good self-reported health, adjusting for age, gender, employment status, chronic musculoskeletal complaints, anxiety and depression.

Conclusions: The adjusted insomnia prevalence estimate in Nord-Trøndelag was 7.9%. Insomnia was strongly associated with poor self-reported health.