Why sleep matters: New study links lack of deep sleep to risk of dementia — what to know

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Consider the odd late-night Netflix binge, or scrolling into the late hours on your phone. Even now, in December, the sunlight has noticeably receded and our routines are feeling off-kilter.

Many things can contribute to poor sleep habits. And though a night of poor sleep can be remedied, studies have shown the detrimental effects of poor sleep over long periods of time.

One thing sleep researchers have been focusing on is the link between sleep and dementia. Read on for everything you need to know about the latest findings.

What is dementia?

According to the Alzheimer's Society of Canada, dementia describes symptoms relating to memory impairment, "caused by disorders affecting the brain."

The agency explained dementia is not a normal part of aging, despite the misconception. It's different from age-associated memory impairment, which impacts about 40 per cent of people over the age of 65.

In Canada, there are more than half a million people living with dementia — a number that's expected to double by 2030 due to an aging population.

Researchers still don't know what causes "most" dementias, but some factors that can increase chances of its development are known. Those include, among others, high blood pressure, smoking, lack of physical activity and social isolation.

Could sleep also be a factor? Here's what we know.

Can poor sleep habits increases chances of dementia?

A study published in JAMA Neurology in late October examined this correlation between deep sleep and dementia. It found that even a subtle one per cent reduction in deep sleep per year, among individuals aged 60 and above, was associated with a higher risk of developing dementia.

The study looked at the experiences of approximately 350 participants who underwent two overnight sleep studies and decades of follow-up, contributing to a nuanced understanding of their sleep patterns. The researchers identified 52 instances of dementia among the study's participants.

Adjusting for variables such as age, gender, and the use of sleep medications, the researchers uncovered a striking correlation: each percentage decrease in deep sleep per year corresponded to a 27 percent higher risk of dementia.

"What's really unique about this article is that it actually provides an objective sleep measure, like slow-wave sleep," said Thanh Dang-Vu, a neurologist and associate director for clinical research at the Institut Universitaire de Gériatrie de Montréal.

Dang-Vu, who is also a professor at Concordia University and the director of the sleep, cognition and neuroimaging laboratory, researches the relationship between sleep and cognition. This includes looking at how important sleep is for memory formation.

Why do sleep patterns matter?

Not all sleep is created equal when it comes to memory formation.

Researchers have honed in on the importance of the different sleep stages, particularly the elusive deep sleep, also known as slow-wave sleep. It is during this stage that sleep researchers and experts say our memories are consolidated and tidied of the mental clutter accumulated throughout the day.

"During sleep, your brain is able to reactivate memories that you acquired before sleep," Dang-Vu explained. "And 'reactivate' means that the brain circuits that were engaged when you were learning this information are replayed during sleep."

Imagine your brain as a bustling library, where books represent memories. As you engage with the world during waking hours, you collect new books. It's during sleep, however, that the librarian meticulously organizes these books, placing them on the proper shelves for future retrieval. This process, known as memory consolidation, is vital for learning and retaining information.

The absence of adequate sleep can be likened to a library with books scattered haphazardly.

Sleep deprivation disrupts the brain's ability to organize and store memories effectively, leading to cognitive lapses and diminished mental sharpness. Everyday tasks become akin to searching for a misplaced book in a disorderly library, with frustration mounting as the brain struggles to recall vital information.

"It has been shown that people with different kinds of sleep disorders, like people with sleep apnea or insomnia, have low performances in memory, in some aspects of attention and concentration or executive functions," Dang-Vu said.

And for those who may not have sleep disorders but might have periods of poor sleep, the short-term effects might lead to long-term consequences.

Consider the familiar scenario of misplacing keys. After a night of insufficient sleep, this simple act can transform into a scavenger hunt. The brain — deprived of its essential organizing time — falters in recalling where the keys were last seen. Multiply this scenario across various aspects of daily life, from forgetting appointments to struggling with decision-making, and the toll of sleep deprivation becomes painfully apparent.

Thanh Dang-Vu said it's important to note, the study may not strictly point to poor sleep as a cause of dementia, since it's known that sleep habits change as we age, and people with dementia may also suffer from poor sleep.

But, he added, sleep is an excellent recommendation when it comes to dementia prevention, and many other health issues.

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