Changes in sleep duration and the risk of incident dementia in the elderly Japanese: the Ohsaki Cohort 2006 Study

STUDY OBJECTIVES: To examine the association between changes in sleep duration and the risk of incident dementia in the elderly. METHODS: In 2006, we conducted a cohort study of 7422 disability-free Japanese individuals aged ≥65 years who lived in Ohsaki City, Japan. In both 1994 and 2006, the individual amount of sleep obtained was assessed using a self-reported questionnaire. Based on sleep duration at these two time points, participants were categorized into five groups according to the change in sleep duration. Data on incident dementia were retrieved from the public Long-term Care Insurance database, and the subjects were followed up for 5.7 years (between April 2007 and November 2012). The Cox proportional hazards model was used to estimate the multivariate-adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for incident dementia. RESULTS: During 36338 person-years of follow up, 688 cases of incident dementia were documented. Compared with subjects who had no change in sleep duration, the multivariate HRs (95% CIs) of incident dementia were 1.31 (1.07 to 1.60) for those whose sleep duration increased by 1 hr, and 2.01 (1.51 to 2.69) for an increase of ≥2 hr. CONCLUSIONS: Increased sleep duration is associated with a significantly higher risk of incident dementia in the elderly. Future studies using well-validated measurements are needed to confirm the association between sleep and dementia.