Sleeping at the limits: the changing prevalence of short and long sleep durations in 10 countries.

Short (≤6 hours) and long (>9 hours) sleep durations are risk factors for mortality and morbidity. To investigate whether the prevalences of short and long sleep durations have increased from the 1970s to the 2000s, we analyzed data from repeated cross-sectional surveys of 10 industrialized countries (38 nationally representative time-use surveys; n = 328,018 adults). Logistic regression models for each country were used to determine changes in the prevalence of short and long sleep durations over time, controlling for sampling differences in gender, age, number of weekend days included, and season of data collection. Over the periods covered by data, the prevalence of short sleep duration increased in Italy (adjusted odds ratio = 2.64, 95% confidence interval (CI): 2.41, 2.89) and Norway (adjusted odds ratio = 2.33, 95% CI: 1.77, 3.08) but decreased in Sweden, the United Kingdom, and the United States. The prevalence of long sleep duration increased in Australia (adjusted odds ratio = 1.14, 95% CI: 1.05, 1.25), Finland (adjusted odds ratio = 1.30, 95% CI: 1.14, 1.48), Sweden (adjusted odds ratio = 1.51, 95% CI: 1.35, 1.69), the United Kingdom (adjusted odds ratio = 2.03, 95% CI: 1.68, 2.46), and the United States (adjusted odds ratio = 1.50, 95% CI: 1.36, 1.65) but decreased in Canada and Italy. No changes were observed in Germany or the Netherlands. Limited increases in short sleep duration challenge the claim of increasingly sleep-deprived societies. Long sleep duration is more widespread than is short sleep duration. It has become more prevalent and thus should not be overlooked as a potential contributor to ill health.