Study objectives: Although sleep curtailment has become widespread in industrialised societies, little work has examined the effects on mortality of change in sleep duration. We investigated associations of sleep duration and change in sleep duration with all-cause, cardiovascular, and non-cardiovascular mortality.
Design: Prospective cohort study. Data are from baseline (Phase 1, 1985-88) and Phase 3 (1991-93), with mortality follow-up of 17 and 12 years respectively.
Setting: The Whitehall II study of 10,308 white-collar British civil servants aged 35-55 at baseline.
Participants: 9781 participants with complete data were included in the analyses at Phase 1, and 7729 of the same participants were included in the analyses at Phase 3 and the analyses of change in sleep duration.
Measurements and results: U-shaped associations were observed between sleep (< or =5, 6, 7, 8, > or =9 hours) at Phase 1 and Phase 3 and subsequent all-cause, cardiovascular, and non-cardiovascular mortality. A decrease in sleep duration among participants sleeping 6, 7, or 8 hours at baseline was associated with cardiovascular mortality, hazard ratio 2.4 (95% confidence intervals 1.4-4.1). However, an increase in sleep duration among those sleeping 7 or 8 hours at baseline was associated with non-cardiovascular mortality, hazard ratio 2.1 (1.4-3.1). Adjustment for the socio-demographic factors, existing morbidity, and health-related behaviours measured left these associations largely unchanged.
Conclusions: This is the first study to show that both a decrease in sleep duration and an increase in sleep duration are associated with an increase in mortality via effects on cardiovascular death and non-cardiovascular death respectively.