This study involved 346 participants aged 60+ who were enrolled in the Framingham Heart Study, who completed two overnight sleep studies from 1995- 1998 and 2001-2003 with an average of 5 years between the two studies. Participants were followed for dementia from their second sleep study to 2018. The analysis revealed that on average the amount of deep sleep between the studies indicated the loss of slow-wave sleep with aging. Over the next 17 years of follow-up, 52 participants developed dementia. Each percentage decrease in deep sleep each year was associated with a 27% increase in the risk of dementia, even after adjusting for various factors.
“Slow-wave sleep, or deep sleep, supports the ageing 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.
“However, to date we have been unsure of the role of slow-wave sleep in the development of dementia. Our findings suggest that slow wave sleep loss may be a modifiable dementia risk factor.”
Associate Professor Pase said that the Framingham Heart Study is a unique community-based cohort with repeated overnight polysomnographic (PSG) sleep studies and uninterrupted surveillance for incident dementia.
“We used these to examine how slow-wave sleep changed with ageing and whether changes in slow-wave sleep percentage were associated with the risk of later-life dementia up to 17 years later,” he said. “We also examined whether genetic risk for Alzheimer’s Disease or brain volumes suggestive of early neurodegeneration were associated with a reduction in slow-wave sleep. We found that a genetic risk factor for Alzheimer’s disease, but not brain volume, was associated with accelerated declines in slow wave sleep.”
