Objective: This study aimed to examine the relationship between sleep duration and all-cause mortality, and to assess the role of cognitive impairment, physical disability, and chronic conditions on this association among very old adults.

Design: A prospective cohort study.

Setting and Participants: Within the Chinese Longitudinal Healthy Longevity Surveys, 17,637 oldest-old aged 80-105 years were followed up to 10 years (2005- 2014).

Measures: Data on sleep duration at baseline were based on self-report and were categorized as short (<7 hour), moderate (7-9 hours), and long sleep (>9 hours). Information on cognitive function using the Mini-Mental State Examination (MMSE), physical disability using Activities of Daily Living (ADL), and chronic conditions including diabetes, heart disease, stroke, asthma, and cancer were collected at baseline based on a structured questionnaire. Information about vital status was ascertained and confirmed by a close family member or village doctor of the participant during the follow-up. Data were analyzed using Cox proportional hazards models, with adjustment for potential confounders.

Results: During the follow-up of 10 years, 11,067 (62.7%) participants died. The multivariate-adjusted hazard ratios (HRs) with 95% confidence interval (CI) for mortality were 1.03 (0.98-1.09) for short sleep and 1.13 (1.08-1.18) for long sleep compared with moderate sleep duration. In stratified analysis by cognitive impairment, physical disability, and chronic conditions, the risk of morality was present only among people with MMSE scores <= 24 but did not differ much when stratified by physical disability and chronic conditions. There was a statistically significant interaction between long sleep and cognitive impairment on mortality (P for interaction = .002).

Conclusions and Implications: Long sleep duration is associated with higher risk of mortality in very old adults independently of health conditions. Cognitive impairment may enhance this association. These findings suggest that health practitioners and families should be aware of the potential adverse prognosis associated with long sleep.