HK-ASAP study: protocol for an observational cohort study on sleep quality, brain reserve and cognitive phenotypes in community-dwelling older adults

Background: The changes of circadian rhythm are very common in senior adults, which can lead to decreased quality of life and jeopardize the brain health in the long run. Among all the types of sleep disturbances, poor sleep quality, as a modifiable condition, can greatly affect the daily activities, cognitive functions, quality of life, and even be implicated as a key potential contributing factor in the development of accelerated cognitive decline and prodromal dementia. Consequently, research efforts to understand, and thus potentially model, the effects of sleep quality on cognition and brain during ageing are of great pragmatic values.Methods: The Hong Kong Cohort of Abnormal Sleep in Ageing Population (HK-ASAP) project is a prospective cohort study recruiting 244 older adults with sleep disturbances. The HK-ASAP study plans to measure sleep quality, brain reserve and cognition at baseline and 2 years. Subjective sleep quality will be assessed by the Pittsburgh Sleep Quality Index (PSQI). Global cognition and domain-specific cognitive functions will be assessed by a comprehensive neuropsychological battery. High-resolution structural magnetic resonance imaging (MRI) data will be acquired and used to quantify the brain reserve, including gray matter volume, cortical thickness, folding and brain age matrices. Saliva samples will be collected for measuring the levels of Aβ40 and Aβ42. Using the data, we will estimate and compare the sleep quality and its associations with cognition, Aβ, and brain reserve in senior adults.Discussion: The bidirectional relationship between sleep quality and cognitive impairments in late adulthood presents an urgent need to understand how poor sleep quality affects cognition and its potential relationship to brain reserve and neuropathological factors. The HK-ASAP study will be a valuable resource for both epidemiological and clinical research, as it will provide fundamental information to identify at-risk individuals. Results from the HK-ASAP study will enable to develop interventions to improve the sleep quality, cognition and healthy longevity in old adults.