Sleep and mortality: a population-based 22-year follow-up study.
STUDY OBJECTIVES
Long and short sleep have been associated with increased mortality. We assessed mortality and 3 aspects of sleep behavior in a large cohort with 22-year follow-up.


DESIGN/SETTING
Prospective, population-based cohort study.


PARTICIPANTS
21,268 twins aged > or =18 years responding to questionnaires administered to the Finnish Twin Cohort in 1975 (response rate 89%), and 1981 (84%).


INTERVENTIONS
N/A.


MEASUREMENTS
Subjects were categorized as short (<7 h), average, or long (>8 h) sleepers; sleeping well, fairly well, or fairly poorly/poorly; no, infrequent, or frequent users of hypnotics and/or tranquilizers. Cox proportional hazard models were used to obtain hazard ratios (HR) for mortality during 1982-2003 by sleep variable categories and their combinations. Adjustments were done for 10 sociodemographic and lifestyle covariates known to affect risk of death.


RESULTS
Significantly increased risk of mortality was observed both for short sleep in men (+26%) and in women (+21%), and for long sleep (+24% and +17%), respectively, and also frequent use of hypnotics/tranquilizers (+31% in men and +39% in women). Snoring as a covariate did not change the results. The effect of sleep on mortality varied between age groups, with strongest effects in young men. Between 1975 and 1981, sleep length and sleep quality changed in one-third of subjects. In men there was a significant increase for stable short (1.34) and stable long (1.29) sleep for natural deaths, and for external causes in stable short sleepers (1.62).


CONCLUSIONS
Our results show complicated associations between sleep and mortality, with increased risk in short and long sleep.