Secular trends in adult sleep duration: a systematic review

Objectives: Little evidence exists to support the common assertion that adult sleep duration has declined. We investigated secular trends in sleep duration over the past 40 years through a systematic review. Methods: Systematic search of 5 electronic databases was conducted to identify repeat cross-sectional studies of sleep duration in community-dwelling adults using comparable sampling frames and measures over time. We also attempted to access unpublished or semi-published data sources in the form of government reports, theses and conference proceedings. No studies were excluded based on language or publication date. The search identified 278 potential reports, from which twelve relevant studies were identified for review. Results: The 12 studies described data from 15 countries from the 1960s until the 2000s. Self-reported average sleep duration of adults had increased in 7 countries: Bulgaria, Poland, Canada, France, Britain, Korea and the Netherlands (range: 0.1-1.7 min per night each year) and had decreased in 6 countries: Japan, Russia, Finland, Germany, Belgium and Austria (range: 0.1-0.6 min per night each year). Inconsistent results were found for the United States and Sweden. Conclusions: There has not been a consistent decrease in the self-reported sleep duration of adults from the 1960s to 2000s. However, it is unclear whether the proportions of very short and very long sleepers have increased over the same period, which may be of greater relevance for public health.