(Montreal) A loss of only 1% of deep slow-wave sleep per year among people aged 60 and over increases their risk of dementia by 27%, warns a new study in which a Montreal researcher participated.
A night’s sleep normally includes several phases of deep slow-wave sleep, which together account for about a fifth of the total sleep time.
“There were already many hypotheses regarding the importance of deep slow-wave sleep for memory […]but this is the first time that we have shown that this loss of deep slow-wave sleep could be associated with an increased risk of developing Alzheimer’s disease years later,” summarized researcher Andrée-Ann Baril, from the ‘Montreal university.
Researchers looked at just under 350 subjects aged 60 and older who were participating in the Framingham Heart Study. Subjects participated in two sleep studies ― the first between 1995 and 1998 and the second between 2001 and 2003 ― with an average time of five years in between.
We then monitored the appearance of signs of dementia in these participants from the second study until 2018. Around fifty cases of dementia were detected during 17 years of follow-up. Even accounting for factors like age, gender, smoking, and use of sleeping pills, antidepressants, and anxiolytics, every one percent decline in deep sleep time increased the risk of dementia.
The exact nature of this association remains to be clarified. Researchers know, however, that it is during the deep sleep phase that the brain eliminates metabolic waste ― such as the proteins that clump together in patients with Alzheimer’s disease. So this could mean that deep sleep is a modifiable risk factor for dementia.
“It is thought that there are several mechanisms of sleep restorative functions that occur (during deep slow-wave sleep),” Ms.me Barrel. There is also an important role in synaptic plasticity and memory, the consolidation of learning which occurs in deep sleep. »
We also do not know exactly in what direction the association is made. Since Alzheimer’s disease develops for several years before the first symptoms appear, it is not impossible that the disease itself is responsible for the disruption of deep slow-wave sleep.
It can also be a vicious circle. We sleep a little less well, it affects the brain, which affects sleep, and so on. Our results suggest an important association with deep slow-wave sleep, but this does not necessarily mean that it causes Alzheimer’s disease.
Andrée-Ann Baril, researcher at the University of Montreal
The scientific data available at the moment suggests that poorer quality sleep could facilitate the pathological processes of Alzheimer’s disease, she added, but the warning signs of Alzheimer’s could also affect the sleep, “so there is a good chance that we are in the presence of a vicious circle here”.
However, other studies have shown that regular physical activity can increase the amount of deep slow-wave sleep.
The findings of this study were published by the medical journal JAMA Neurology.