HIGHER DEMENTIA RISK AT AGE 90+ IS ASSOCIATED WITH SHORT SLEEP A QUARTER OF A CENTURY EARLIER: THE 90+ STUDY

Abstract

Short sleep has been linked to an increased risk of dementia in several studies. Although dementia risk is highest in the oldest-old (aged 90 or older) and sleep problems become more prevalent with age, the relationship between dementia risk and sleep at this age has not been studied. Our aim is to examine the risk of dementia in the oldest-old in relation to sleep reported on average 24 years earlier. We analyzed data on 581 participants with no dementia at baseline from The 90+ Study. These participants had reported on sleep as part of the Leisure World Cohort Study 16–36 years before joining The 90+ Study, when they were on average 69 years of age (range: 54–84 years). We analyzed self-reported nocturnal sleep duration, napping, and 24-hour sleep duration (sum of nocturnal sleep and nap duration). Sleep duration was categorized into <6, 6, 7, 8 and ≥9-hour groups. As part of The 90+ Study, participants were assessed for dementia (DSM-IV) every six months. Cox regression was used to estimate the hazard ratios (HR) for the sleep variables in relation to risk of dementia, controlling for age, sex, and education. Participants were on average 93 years old (range: 90-103) at The 90+ Study baseline visit and most were women (72%). 275 participants developed dementia during follow-up (mean=3 years; range: 0.4 – 13.8 years). Short (<6 hours) nocturnal sleep, reported 16–36 years earlier, was significantly associated with an increased risk of dementia (HR=1.70) compared with optimal sleep (8 hours) (Table). Short 24-hour sleep (<6 hours) showed a non-significant increased dementia risk (HR=1.57) compared with optimal sleep. Dementia risk did not differ between those who napped and those who did not. Increased risk of dementia in the oldest-old is associated with short sleep duration reported 16–36 years earlier. Possible explanations for this relationship include poor amyloid clearance, brain atrophy, systemic inflammation, and comorbidities. Early identification of and intervention for sub-optimal sleep duration may be beneficial for maintaining cognition in the oldest-old.