Sleep habits in older adults in Ireland: Associations with physical and cognitive function

Abstract

Sleep acts as the rest cycle for the body, during which restorative processes such as muscle growth, repair and memory consolidation occur. Sleep duration and chronotype have been identified as areas of interest to improve healthy ageing in older adults. The study of sleep is complex, with numerous interacting factors contributing to worse sleep behaviours. This thesis aimed to investigate the sleep habits of older community-dwelling adults in Ireland. Data were from The Irish Longitudinal Study on Ageing, a nationally representative study of community-dwelling adults aged 50 years and older in Ireland. Self-reported sleep was captured using survey questions and objective sleep measured using accelerometer devices. Study 1 established baseline findings of objective sleep duration in older adults in Ireland, identifying social and health correlates, many of which are modifiable, of impaired sleep duration. Study 2 assessed discrepancies between measurements of self-reported and objective sleep duration. Disagreement between self-reported and objective measures of sleep duration was found, with insomnia symptoms shown to be an independent driving factor. Study 3 measured cross-sectional associations between sleep duration, sleep quality and cognition. Long self-reported sleep duration, short objectively measured sleep duration, and sleep quality were all associated with worse cognitive performance. Study 4 was a longitudinal analysis of sleep duration and cognitive function trajectories using repeated cognitive assessments. Long self-reported sleep duration was consistently associated with a decline in performance at two-, four- and six-year follow-up periods. Study 5 was a longitudinal analysis which assessed sleep chronotype as a risk factor for physical frailty. Late sleep chronotypes were associated with an increased risk of developing frailty. This thesis established important associations between sleep, cognitive and physical function in a large sample of older, community-dwelling adults. Interventions to improve sleep and address the underlying conditions which lead to impaired sleep will contribute to the healthy ageing of our older population.