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Longevity Briefs: More Evidence That Deep Sleep Helps Prevent Dementia

Posted on 11 June 2024

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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

As we age, the risk of developing dementia increases, and one potential contributing factor is the amount of slow-wave sleep we get. Slow-wave sleep is the deepest and most restorative stage of our sleep cycle. During slow wave sleep, neurons throughout the brain activate slowly and in synchrony, like a crowd of people chanting in unison. This causes a pattern of slow, large brainwaves from which this sleep stage gets its name.

Slow wave sleep seems to be important for learning and memory, as well as the clearance of waste products from the brain. These waste products include the misfolded proteins that seem to play a role in neurodegenerative diseases. Since time spent in slow-wave sleep shortens with increasing age, scientists have speculated that loss of slow-wave sleep may contribute to the development of dementia. Previous studies show that people who get more slow-wave sleep are less likely to develop dementia, but are unable to prove a causal link.

The discovery:

In this paper, researchers looked at 346 participants of the Framingham heart study, in which participants are followed up over an extended period and various lifestyle and health factors are monitored, including overnight sleep studies. Participants were at least 60 years old and had no dementia at the time of the first sleep recordings which occurred in the late 1990s. 

Researchers found that the percentage of sleeping time spent in slow wave sleep decreased with age, and that the extent of this decrease correlated with the risk of developing dementia later on. Each percentage point of slow wave sleep loss per year was associated with a 27% increase in dementia risk, and an even larger (32%) increase in the risk of Alzheimer’s disease specifically. This was after controlling for confounding factors like smoking and genetic risk of dementia. However, researchers also found that being genetically predisposed to developing dementia was associated with accelerated declines in slow-wave sleep.

The implications:

The study provides more evidence that a loss of slow-wave sleep is associated with an increased risk of developing dementia later on. Specifically, it suggests that a more rapid decline in slow-wave sleep duration predicts greater risk of dementia later on. However, this study still doesn’t prove that loss of slow-wave sleep causes dementia and not the other way around. Subtle changes in the brain that precede dementia by decades might lead to sleep disruptions, an idea supported by the fact that genetic risk of dementia was associated with a more rapid loss of slow-wave sleep. On the other hand, studies in animal models (and a few in humans) suggest that enhancing slow-wave sleep leads to cognitive benefits like[such as] improved memory. It seems likely that this relationship works both ways and we can be hopeful that sleep interventions would have some benefit for preventing dementia in humans.

If you want to learn more about how you can improve your sleep quality, check out part 3 of our sleep optimising guide.

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    Association Between Slow-Wave Sleep Loss and Incident Dementia

    Title image by Gregory Pappas, Upslash

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