Less than a 1 percent decrease in deep sleep per year for people over 60 translates to a 27 percent increase in dementia risk, according to a study that suggests increasing or maintaining deep sleep, also known as slow wave sleep, may stave off dementia in older years.
The research, led by Associate Professor Matthew Pass of the Monash School of Psychological Sciences and Turner Institute for Brain and Mental Health in Melbourne, Australia, was published today. Jama NeurologyLooked at 346 participants over age 60 enrolled in the Framingham Heart Study who completed two overnight sleep studies between 1995 to 1998 and 2001 to 2003, with an average of five years between the two studies.
These participants were then carefully followed for dementia from the time of the second sleep study until 2018. The researchers found, on average, the amount of deep sleep decreased between the two studies, indicating a loss of slow-wave sleep with aging. Over the next 17 years of follow-up, there were 52 cases of dementia. Even after adjusting for age, sex, cohort, genetic factors, smoking status, sleeping pill use, antidepressant use, and anxiolytic use, each percentage reduction in deep sleep per year was associated with a 27 percent increase in dementia risk.
Slow-wave sleep, or deep sleep, supports the aging brain in many ways, and we know that sleep increases the clearance of metabolic waste from the brain, including the clearance of proteins that aggregate in Alzheimer’s disease.
However, until today we were uncertain about the role of slow-wave sleep in the development of dementia. “Our findings suggest that loss of slow wave sleep may be a modifiable dementia risk factor.”
Associate Professor Matthew Pass from the Monash School of Psychological Sciences and Turner Institute for Brain and Mental Health in Melbourne, Australia
Associate Professor Pass said 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 changes with aging and whether changes in the percentage of slow-wave sleep were associated with later-life dementia risk after 17 years,” he said.
“We also examined whether genetic risk for Alzheimer’s disease or brain volume indicative of early neurodegeneration was associated with a decline in slow-wave sleep. We found that a genetic risk factor for Alzheimer’s disease, but not brain volume, was associated with accelerated decline. Slow-wave sleep .”
Himali, J.J., etc (2023) Association between slow-wave sleep loss and incident dementia. Jama Neurology. doi.org/10.1001/jamaneurol.2023.3889.