Association of sleep duration at age 50, 60 and 70 with incidence of dementia

Abstract

AbstractBackgroundSleep dysregulation is a feature of dementia but whether sleep duration prior to old age is also associated with incidence of dementia remains unclear. We examined the association of sleep duration in midlife with risk of late‐life dementia.MethodData were drawn from 7959 participants (women=33.0%) of the Whitehall II cohort study, established in 1985‐1988, from which self‐reported sleep duration at age 50, 60, and 70 was extracted and categorized as “short: ≤6 hours per night”, “normal: 7 hours per night”, “long: ≥8 hours per night”. Incident dementia (N=521) cases were identified through electronic health registers until March 2019.ResultCompared to normal sleep duration, higher risk of incident dementia was observed among those with short sleep duration at ages 50 and 60 (mean follow‐up 25 and 15 years, respectively), although not significantly at age 70 (hazard ratio 1.22 (95% confidence interval 1.01‐1.48), 1.37 (1.10‐1.72), and 1.24 (0.98‐1.57), respectively). Persistent short sleep duration at age 50, 60, and 70 compared to persistent normal sleep duration was also associated with a 32% (hazard ratio 1.32 (1.02‐1.72)) increased risk of dementia independently of sociodemographic, behavioural, cardiometabolic, and mental health factors. These associations were also evidence when analyses were restricted to participants without a history of mental illness before age 65 years. In a subsample with objective measure of sleep (accelerometer data, N=3888), the association of short sleep duration with increased risk of dementia was confirmed.ConclusionThis study paying attention to both age at sleep duration and length of follow‐up along with inclusion of a wide array of covariates shows that short sleep duration in midlife is associated with an increased risk of dementia. Public health messages to encourage good sleep hygiene, may be particularly important for people at higher risk of dementia.