Study objective: To report the distribution of various sleep parameters in a population-based study.
Design: Population-based cross-sectional study with self-administered questionnaires.
Setting: Conducted as part of the Hordaland Health Study '97-'99 in collaboration with the Norwegian National Health Screening Service.
Participants: 8860 subjects, aged 40 to 45 years, answered the sleep questionnaire part of the study.
Interventions: N/A.
Measurements and results: Reports on habitual bedtimes, rise times, subjective sleep need, and various sleep characteristics were used in this study. Mean (+/- SD) nocturnal sleep duration during weekdays in men was 6 hours 52 minutes (+/- 55 minutes); in women 7 hours 11 minutes (+/- 57 minutes). Mean subjective sleep need was 7 hours 16 minutes (+/- 52 minutes) in men; 7 hours 45 minutes (+/- 52 minutes) in women. Sleep duration was shorter in shift workers and longer in married subjects and in those living in rural areas. Subjective sleep need was higher in subjects reporting poor subjective health and in subjects living in rural areas. In total, these variables accounted for only around 3% of the variance in sleep duration and sleep need. Ten percent of the men and 12.2% of the women reported frequent insomnia.
Conclusions: The wide distribution of sleep duration and subjective sleep need indicate large interindividual variations in these parameters. There were pronounced sex differences in these variables and in most of the sleep characteristics studied. Shift work, urban-rural living, marital status, and education in men were sources of significant, but small, variations in sleep duration.