Secular trends in adult sleep duration: a systematic review.
Level 3 - non-randomized controlled study
Systematic review of repeat cross-sectional observational surveys, graded by non-clinical design analogy.
PubMed 22075214 · doi:10.1016/j.smrv.2011.07.003
What was done
Authors conducted a systematic review across five electronic databases and grey literature (theses, conference proceedings, government reports) without language or date limits to evaluate adult sleep duration trends over 40 years. They included repeat cross-sectional studies of community-dwelling adults using comparable sampling methods and measures over time. Twelve studies covering 15 countries from the 1960s to the 2000s were identified from 278 potential reports.
What was found
Self-reported adult sleep duration did not consistently decline across nations. Average sleep duration increased in seven countries (Bulgaria, Poland, Canada, France, Britain, Korea, Netherlands) by 0.1 to 1.7 minutes per night each year. Average sleep duration decreased in six countries (Japan, Russia, Finland, Germany, Belgium, Austria) by 0.1 to 0.6 minutes per night each year. Results were inconsistent across surveys for the United States and Sweden.
Why it matters
The findings challenge the widespread assumption that modern adult populations universally sleep less than previous generations. Secular trends in average sleep duration appear country-specific rather than universally declining.
Limits
All included studies relied on subjective self-reported sleep duration rather than objective recordings. The synthesis examined mean sleep duration and could not determine whether tails of the distribution (proportions of very short or very long sleepers) changed over time.
Cited by
- contradicts Global total sleep time has decreased by approximately 60 minutes over the last 60 years.