A new study has found that, in people over 60, a reduction in deep sleep by as little as 1% per year equated to a 27% increased risk of dementia. The findings suggest that enhancing or maintaining deep sleep may be a way of keeping the disease at bay.
Slow-wave sleep, often called deep sleep, usually lasts between 70 and 90 minutes and occurs during the first hours of the night. In addition to being the type of sleep that makes you wake up feeling refreshed, during deep sleep, the body repairs muscles, bones, and tissues and strengthens the immune system.
Previous studies have suggested that the brain clears away toxic dementia-related proteins during deep sleep, but the role of deep sleep in the development of dementia remains ambiguous. Now, the results of a new study by researchers at Monash University suggest that a reduction in deep sleep is related to dementia risk in people over 60.
“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,” said Matthew Pase, one of the study’s co-authors. “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.”
The researchers recruited 346 participants who’d undertaken two overnight sleep studies in the periods 1995 to 1998 and 1998 to 2001. The mean age of the participants was 69, and around half (52%) were female.
“We used these [sleep studies] 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,” Pase said.
The researchers found that, on average, the amount of sleep declined between the two sleep studies, indicating that aging was associated with a loss of deep sleep.
Over 17 years of follow-up, there were 52 dementia cases. Adjusting for age, sex, genetic factors, smoking status, use of sleeping, anti-anxiety and antidepressant medications, each percentage decrease in deep sleep per year was associated with a 27% increase in dementia risk.
The researchers also found that the loss of deep sleep with aging was accelerated in the presence of Alzheimer’s disease genetic risk – the APOE e4 allele – but changes in brain volume weren’t.
“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,” Pase said. “We found that a genetic risk factor for Alzheimer’s disease, but not brain volume, was associated with accelerated declines in slow-wave sleep.”
The study was published in the journal JAMA Neurology.
Source: Monash University