Further research is necessary in order to investigate whether poor sleep can be a potential risk factor for dementia.
Due to an insignificant amount of data that includes follow-ups and objective measures of sleep, researchers have been uncertain whether poor sleep can be a potential dementia risk.
To study associations between polysomnography (PSG)-derived sleep and the risk of dementia and related cognitive conditions, The Sleep and Dementia Consortium was established. In a recent study, researchers wanted to find potential associations between sleep and dementia.
Based on a combination of previous smaller scaled studies, researchers wanted to find which sleep variables are linked to cognition, what cognitive domains are influenced by differences in sleep, and whether there are systematic differences by key variable (i.e., sex and APOE ε4 genotype).
The study evaluated 5946 adults at least 45 years of age without stroke or dementia across 5 population-based cohorts (Atherosclerosis Risk in Communities [ARIC] study, Cardiovascular Health Study [CHS], Framingham Heart Study [FHS], Osteoporotic Fractures in Men Study [MrOS], and Study of Osteoporotic Fractures [SOF]) to determine whether there is an association of sleep architecture and obstructive sleep apnea (OSA) with cognitive function.
Participants completed at-home PSGs, where electrooculogram, electromyogram, thoracic, and abdominal displacement (inductive plethysmography bands), airflow (nasal-oral thermocouples), finger pulse oximeter, a single bipolar electrocardiogram, body position by a mercury gauge sensor, and ambient light were all recorded.
The different sleep stages—stage 1 (N1), stage 2 (N2), stage 3 (N3), and rapid eye movement (REM) sleep—were expressed as a percentage of total sleep time duration. In addition, the Epworth Sleepiness Scale (ESS), an 8-item questionnaire to determine the likelihood of falling asleep, was used to measure sleepiness during the daytime.
Results indicate that better sleep consolidation and the absence of OSA were linked to superior general cognitive function, and normal sleep duration was shown to be associated with better attention and processing speed. Though there are both direct (e.g., sleep fragmentation or intermittent hypoxia leading to ischemic brain injury) and indirect (e.g., cardiovascular instability or systemic inflammation) mechanisms that possibly link OSA with poorer cognition, conclusions regarding causation could not be made from this study. Further, there was no association found between sleep architecture and verbal learning and memory found in the study.
Compared to individuals who were referred clinically for PSG, those diagnosed with OSA based on incidental findings may have different characteristics, such as comorbidities, overall dementia risk factor burden, and the severity of sleep disturbances. In addition, there were no consistent patterns of interactive associations to suggest that sex, APOE ε4, or excessive daytime sleepiness interacted with associations.
Previously, it was believed that sleep stage percentages were associated with global cognition, although this evidence was not present across cohorts. N3 sleep plays a significant role in memory consolidation, although associations between N3 percentage and cognitive function were not found, which is consistent with a previous study that found no connection between N3 sleep time and dementia. The researchers of the current study acknowledge that associations between N3 and cognition may differ by variables that were not taken into consideration (e.g., cognitive status or brain amyloid burden).
Limitations of this study include the fact that sleep and cognition were assessed only once and that longer follow-up durations are necessary due to sleep and brain health likely being bidirectional. It is important to note that it is unclear whether there are sensitive periods in adult life in which good sleep is essential for preventing cognitive impairment later in life.
Pase MP, Harrison S, Misialek JR, et al. Sleep Architecture, Obstructive Sleep Apnea, and Cognitive Function in Adults. JAMA Netw Open. 2023;6(7):e2325152. doi:10.1001/jamanetworkopen.2023.25152