Prevalence of insomnia in the adult Norwegian population

A representative adult sample (18 years and above) of the Norwegian populat ion, comprising 2001 subjects, participated in telephone interviews, focusi ng on the one-month point prevalence of insomnia and use of prescribed hypn otics. Employment of DSM-IV inclusion criteria of insomnia yielded a preval ence rate of 11.7%. Logistic regression analysis performed on the different insomnia symptoms revealed that somatic and psychiatric health were the st rongest predictors of insomnia, whereas gender, age, and socioeconomic stat us showed a more inconsistent relationship. Use of prescribed hypnotic drug s was reported by 6.9% and was related to being female, elderly, and having somatic and emotional problems. Sleep onset problems and daytime impairmen t were more common during winter compared to summer. Use of hypnotics was m ore common in the southern (rather than the northern) regions of Norway. Fo r sleep onset problems a Season x Region interaction was found, indicating that the prevalence of sleep onset problems increased in southern Norway fr om summer to winter, while the opposite pattern was found in the northern r egions. The importance of clinically adequate criteria and seasonal variati on in the evaluation of insomnia is briefly discussed.