Investigation of the relationship between sleep duration, all-cause mortality, and preexisting disease.

OBJECTIVE: To examine the relationship between sleep duration and mortality and to quantify the likely impact of residual confounding due to poor health status on any observed association.
METHODS: The sample included 227,815 Australian adults aged 45 years and older recruited from 2006-2009 (the 45 and Up Study). Sleep duration and relevant covariates (e.g., health status, demographic factors) were assessed through a self-report questionnaire. These data were linked with mortality data from the New South Wales Registry of Births, Deaths, and Marriages up to December 2010 (mean follow-up period, 2.8 y). Cox proportional hazards models examined the relationship between sleep duration and all-cause mortality adjusting for relevant sociodemographic covariates (e.g., age, gender, marital status), with further stratification by baseline health status based on physical functioning and preexisting disease.
RESULTS: The adjusted mortality risk was significantly higher in individuals reporting <6 hours of sleep (hazard ratio [HR], 1.13[1.01-1.25]) and ≥10 hours of sleep (HR, 1.26[1.16-1.36]), compared to those reporting 7 hours of sleep per night. These associations differed by baseline health status (p[interaction]=0.026) such that there was no significant relationship of sleep duration to mortality in those with good health at baseline.
CONCLUSION: Following careful prospective controlling for baseline health, mortality risk does not significantly vary according to sleep duration. Previous findings suggesting a relationship between sleep duration and mortality could be affected by residual confounding by poor preexisting health, as reflected by a combination of preexisting illnesses and functional limitations.