Sleep is a fundamental component of our daily lives, and its significance in maintaining overall health has been increasingly recognized. Within the realm of sleep, slow-wave sleep (SWS) stands out as a crucial stage with potential implications for brain health and dementia.
While previous research has indicated that SWS supports the aging brain, particularly in clearing proteins associated with Alzheimer’s disease, the connection between SWS and dementia development remains somewhat unclear. This prospective cohort study aimed to investigate the relationship between SWS loss due to aging, genetic risk factors for Alzheimer’s disease, and the risk of incident dementia.Â
This study involved participants from the Framingham Heart Study who underwent two overnight polysomnography (PSG) studies between 1995-2008. To be included in the study, individuals had to be aged 60 or older and free from dementia at the time of their second PSG. The data analysis was conducted from January 2020 to August 2023, and the primary exposure variable was the change in SWS percentage measured across the two PSG studies, with a mean time interval of 5.2 years.Â
The study cohort consisted of 346 participants with an average age of 69 years, and slightly more than half were female. The data revealed that SWS declined with age across the two PSG studies, showing an average annual decrease of 0.6% in SWS percentage. Over the subsequent 17-year follow-up period, 52 cases of incident dementia were documented.Â
To understand the relationship between SWS loss and dementia risk, Cox regression models were employed, adjusting for various factors, including age, sex, APOE ε4 allele presence, smoking status, use of sleeping medications, antidepressants, and anxiolytics. The results indicated that for each percentage decrease in SWS per year, there was a 27% increase in the risk of developing dementia (hazard ratio, 1.27; 95% CI, 1.06-1.54; P = 0.01). In essence, the more SWS individuals lost as they aged, the higher their risk of dementia.Â
Furthermore, the study explored how genetic factors associated with Alzheimer’s disease and hippocampal volumes, indicative of early neurodegeneration, influenced SWS loss. It was found that SWS loss was accelerated in the presence of the APOE ε4 allele, a known genetic risk factor for Alzheimer’s disease. However, hippocampal volumes measured near the time of the first PSG did not significantly impact the rate of SWS decline.Â
This cohort study sheds light on the relationship between slow-wave sleep loss and the risk of incident dementia. It demonstrates that SWS percentage declines with both age and the presence of Alzheimer’s disease genetic risk factors, and a more substantial reduction in SWS is associated with a higher risk of developing dementia. These findings underscore the potential modifiability of dementia risk factors by addressing sleep-related issues, specifically SWS loss.Â
Understanding the complex interplay between sleep, aging, and genetic factors like APOE ε4 in dementia risk is essential for developing strategies to prevent or mitigate the impact of this devastating condition. As research in this area progresses, interventions to promote SWS and overall sleep quality could emerge as valuable tools in the fight against dementia.Â
Journal Reference Â
Himali JJ, Baril A, Cavuoto MG, et al. Association Between Slow-Wave Sleep Loss and Incident Dementia. JAMA Neurol. Published online October 30, 2023. doi:10.1001/jamaneurol.2023.3889Â
