Could how well you sleep be linked to diseases like dementia?

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A new peer-reviewed publication suggests quality of sleep could be linked to a higher risk of dementia.

In a new academic article published Thursday, Dr. Maiken Nedergaard, a neuroscientist from the University of Rochester Medicine, suggests conditions like chronic stress, depression, cardiovascular disease, fragmented sleep, aging, and cognitive decline are all connected to quality of sleep.

“The article presents a new way of thinking about sleep, not simply as a period of rest, but as a highly organized biological state that co-ordinates brain chemistry, blood vessel movement and cerebrospinal fluid flow to support the brain’s nightly cleaning process,” a news release said.

“Sleep is not a quiet or inactive state,” Nedergaard said in the news release. “During sleep, the brain shifts into a co-ordinated rhythm that appears to support one of its most important housekeeping functions.”

“For decades, we thought about sleep primarily in terms of memory and restoration,” she added. “What is emerging now is the idea that sleep is also a highly organized fluid-transport state that helps maintain brain health.”

What are neuromodulators?

According to the neuroscientist, the crux of the matter lies in understanding the role of neuromodulators.

Neuromodulators are chemicals in the brain – like norepinephrine, serotonin, dopamine, and acetylcholine – that regulate mood, attention, learning and behaviour in a person when they’re awake.

According to the neuroscientist, the neuromodulators act “fairly independently” when a person is awake, with each performing a function separate from the others.

“But when we go to bed and we sleep, they oscillate in synchrony,” Nedergaard told CTVNews.ca.

During non-REM sleep – the quiet, restful phase of sleep that accounts for nearly 80 per cent of total sleep time – these chemical systems behave differently, the review explains, becoming “synchronized into slow, repeating oscillations” that occur roughly every minute. These oscillations, or “rhythms,” are linked to changes observed in brain activity, heart rate, movement of blood vessels and the flow of cerebrospinal fluids.

These rhythms help power the body’s glymphatic system – the brain’s waste clearing network – by creating slow, rhythmic changes in blood vessel sizes known as “vasomotion.”

When these rhythms get disrupted by a number of factors, Nedergaard says the brain can become less efficient at flushing out toxic proteins, adding that many disorders that disrupt the brain’s sleep patterns can also increase the risk of cognitive disorders like dementia.

“Our work suggests these may not be separate phenomena,” she said. “They may be connected through the brain’s ability to clear waste during sleep.”

According to Nedergaard, these neurodegenerative diseases are driven by the accumulation of waste proteins like amyloid, tau and alpha-synuclein in the brain.

“When the brain doesn’t clean itself sufficiently, you get an inflammatory response, because that’s how the brain’s immune cell is engineered,” she said, adding that this results in nerve cells “dying” due to a less-than-optimal environment, leading to dementia.

Does irregular sleep lead to dementia?

Meanwhile, a sleep specialist and nursing professor emeritus at the University of British Columbia says this review is a “step forward,” due to the limited understanding surrounding the link between protein buildup in the brain and dementia.

Wendy Hall told CTVNews.ca that although there has been an understanding of the idea of clearance in the brain during sleep, there has not been enough discussion about how it might occur.

“This is a new concept – this idea that these systems that work in parallel with one another in wakefulness, actually work in synergy when you’re sleeping at night,” Hall said.

However, she noted that this is based on a review of many other studies and that other issues, such as psychiatric problems, traumatic brain injury and substance abuse, can also interfere with neuromodulators. There are also several medications that can influence this system.

Speaking about prior evidence regarding the connection between sleep and neurodegenerative diseases, Hall said there has been earlier research suggesting it.

“Does the dementia cause sleep dysregulation, or does the sleep dysregulation contribute to the dementia?” she said. “They (the author) believe that the link there is that the normal things that are secreted when you’re in sleep mode aren’t being secreted in the same way because of sleep dysregulation and sleep fragmentation, and short sleep duration, thereby putting you at more risk.”

Heartbeat timing

The review also noted that subtle changes in the timing between heartbeats could be a possible biomarker of “sleep-related brain health.”

Researchers have found that the fluctuations in heart rate during sleep appeared to be in tandem with the neuromodulator rhythms occurring in the brain.

Nedergaard believes that monitoring a person’s heart rate could eventually become a “non-invasive” method of monitoring the brain’s clearance system at night, potentially being used to identify people at increased risk for cognitive decline before symptoms appear.

“If your heart rate goes up about every minute and then down, it’s great, and you have a good prognosis for not getting dementia,” she said. “If your heart rate variability is low, meaning that it’s pretty constant all during sleep, your risk of getting dementia is higher.”

According to Hall, if this is true, it could be easily monitored using wearable “smart” devices that track your health, fitness and daily activity levels.

“You could easily put an Apple Watch on somebody and look at what their heart rate variability is over the course of the day, right?” she said.