Even a 1% reduction in deep sleep per year for people over 60 years old translates into a 27% increased risk of dementia, according to a new study. The finding suggests that enhancing or maintaining deep sleep, also known as slow wave sleep, in older years could stave off dementia.
The study, led by Associate Professor Matthew Pase of the Monash School of Psychological Sciences and the Turner Institute for Brain and Mental Health in Melbourne, Australia, looked at 346 Framingham Heart Study participants over 60 years old who completed two overnight sleep studies from 1995 to 1998 and 2001 to 2003, with an average of five years between the two studies.
Slow-wave sleep, or deep sleep, supports the aging brain in many ways, and we know that sleep augments the clearance of metabolic waste from the brain, including facilitating the clearance of proteins that aggregate in Alzheimer’s disease,
Associate Professor Pase said.
Deep Sleep Loss
From the start of the second sleep study until 2018, the subjects were closely monitored for dementia. The researchers discovered that the amount of deep sleep decreased on average between the two experiments, showing that slow wave sleep loss occurs with aging. There were 52 cases of dementia over the next 17 years of follow-up.
Even adjusting for age, sex, cohort, genetic factors, smoking status, sleeping medication use, antidepressant use, and anxiolytic use, each percentage decrease in deep sleep each year was associated with a 27% increase in the risk of dementia.
Until now, researchers have been unsure about the function of slow-wave sleep in the development of dementia. These data show that slow wave sleep loss may be a modifiable dementia risk factor.
Genetic Factors
According to Associate Professor Pase, the Framingham Heart Study is a unique community-based cohort with repeated overnight polysomnographic (PSG) sleep studies and continuous surveillance for incident dementia.
“We used these to examine how slow-wave sleep changed with aging and whether changes in slow-wave sleep percentage were associated with the risk of later-life dementia up to 17 years later,”
he said.
They also investigated whether a decline in slow-wave sleep was connected with a genetic predisposition for Alzheimer’s Disease or brain volumes suggestive of early neurodegeneration. The results showed that a genetic risk factor for Alzheimer’s disease was connected with increased decreases in slow wave sleep but not brain volume.
Abstract
Importance Slow-wave sleep (SWS) supports the aging brain in many ways, including facilitating the glymphatic clearance of proteins that aggregate in Alzheimer disease. However, the role of SWS in the development of dementia remains equivocal.
Objective To determine whether SWS loss with aging is associated with the risk of incident dementia and examine whether Alzheimer disease genetic risk or hippocampal volumes suggestive of early neurodegeneration were associated with SWS loss.
Design, Setting, and Participants This prospective cohort study included participants in the Framingham Heart Study who completed 2 overnight polysomnography (PSG) studies in the time periods 1995 to 1998 and 1998 to 2001. Additional criteria for individuals in this study sample were an age of 60 years or older and no dementia at the time of the second overnight PSG. Data analysis was performed from January 2020 to August 2023.
Exposure Changes in SWS percentage measured across repeated overnight sleep studies over a mean of 5.2 years apart (range, 4.8-7.1 years).
Main Outcome Risk of incident all-cause dementia adjudicated over 17 years of follow-up from the second PSG.
Results From the 868 Framingham Heart Study participants who returned for a second PSG, this cohort included 346 participants with a mean age of 69 years (range, 60-87 years); 179 (52%) were female. Aging was associated with SWS loss across repeated overnight sleep studies (mean [SD] change, −0.6 [1.5%] per year; P < .001). Over the next 17 years of follow-up, there were 52 cases of incident dementia. In Cox regression models adjusted for age, sex, cohort, positivity for at least 1 APOE ε4 allele, smoking status, sleeping medication use, antidepressant use, and anxiolytic use, each percentage decrease in SWS per year was associated with a 27% increase in the risk of dementia (hazard ratio, 1.27; 95% CI, 1.06-1.54; P = .01). SWS loss with aging was accelerated in the presence of Alzheimer disease genetic risk (ie, APOE ε4 allele) but not hippocampal volumes measured proximal to the first PSG.
Conclusions and Relevance This cohort study found that slow-wave sleep percentage declined with aging and Alzheimer disease genetic risk, with greater reductions associated with the risk of incident dementia. These findings suggest that SWS loss may be a modifiable dementia risk factor.
Reference:
- Himali JJ, Baril A, Cavuoto MG, et al. Association Between Slow-Wave Sleep Loss and Incident Dementia. JAMA Neurol. (Oct. 2023) doi:10.1001/jamaneurol.2023.3889