A new study involving a Montreal researcher warns that losing just 1% of deep, slow-wave sleep per year in people aged 60 or older increases the risk of dementia by 27%.
Nighttime sleep typically involves several stages of deep, slow-wave sleep, which together account for about one-fifth of total sleep time.
“There have already been many hypotheses regarding the importance of deep slow-wave sleep for memory (…), but this is the first time we have shown that the loss of this deep slow-wave sleep can be associated with an increased risk of cancer.” “Alzheimer’s disease develops years later,” concluded researcher André-Anne Baril, from the University of Montreal.
The researchers looked at just under 350 people aged 60 or older who were participating in the Framingham Heart Study. Participants took part in two sleep studies — the first between 1995 and 1998 and the second between 2001 and 2003 — with an average interval of five years in between.
We then monitored the emergence of signs of dementia in these participants from the second study until 2018. About fifty cases of dementia were detected during the 17 years of follow-up. Even taking into account factors such as age, gender, smoking, use of sleeping pills, antidepressants and anxiolytics, every 1% decrease in deep sleep time increases the risk of dementia by 27%.
The exact nature of this association remains to be clarified. However, researchers know that during deep sleep the brain gets rid of metabolic waste, such as proteins that clump together in Alzheimer’s patients. So this may mean that deep sleep is a modifiable risk factor for dementia.
“We think there are several mechanisms for restorative sleep functions that occur[during deep slow-wave sleep],” Burrell said. There is also an important role for synaptic plasticity, memory, and enhanced learning that occurs during deep sleep.
We also do not know exactly in which direction the correlation is established. Since Alzheimer’s disease develops for several years before the first symptoms appear, it is not impossible that the disease itself could be responsible for the deep slow-wave sleep disorder.
“It can also be a vicious cycle,” Ms Burrell said. We sleep less well, it affects the brain, which affects sleep, etc. Our results suggest a significant association with deep slow-wave sleep, but this does not necessarily mean that it causes Alzheimer’s disease.
She added that currently available scientific data suggests that poor sleep quality can facilitate the pathological processes of Alzheimer’s disease, but the warning signs of Alzheimer’s disease can also affect sleep, “so there is a good chance that we are in a vicious cycle here.”
However, other studies have shown that regular physical activity can increase the amount of deep slow-wave sleep.
The results of this study were published in the medical journal JAMA Neurology.