Association between sleep duration and all-cause mortality in old age: 9-year follow-up of the Bambuí Cohort Study, Brazil

This study investigates the association of sleep duration with risk of all-cause mortality among elderly Brazilians using data from a 9-year population-based cohort study and applying a multivariable longitudinal categorical and continuous analysis using Cox's proportional hazards models. This analysis used data from the Bambui Health and Ageing Study (BHAS), conducted in Bambuí city (approximately 15000 inhabitants) in southeastern Brazil. The study population comprised 1512 (86.8%) of all eligible 1742 elderly residents. In multivariable analysis, using sleep duration as categorical variable and controlling for multiple measures of sociodemographic and health status, those who slept 9h or more per night were found to be at higher risk of mortality than those who slept 7h hazard ratio (HR): 1.53; 95% confidence interval (CI): 1.12-2.09. Excluding those whose deaths occurred within 2years after entry, this association remained significant (HR: 1.56; 95% CI: 1.12-2.18). In analyses using sleep duration as a continuous variable, a linear correlation was found between sleep duration and mortality in all adjusted models in the whole sample (HR: 1.08; 95% CI: 1.02-1.15) and following exclusion of those whose deaths occurred within 2years after entry (HR: 1.13; 95% CI: 1.06-1.21). Both linear and quadratic terms were significant, reflecting a predicted relationship, with mortality predominantly increasing in association with long sleep duration but with the addition of a slight decrease in association with shorter sleep duration. In conclusion, long rather than short sleep duration was associated principally with all-cause mortality in this sample. It is therefore reasonable to suggest that clinicians should be aware of the potential adverse prognosis associated with prolonged sleep.