Keeping track of the health and lifestyle factors tied to dementia is proving to be increasingly challenging.
Recent research has identified various elements of our lives that might contribute to the risk of developing dementia later on.
Some of these factors are fairly easy to change, like brain exercises, diet, and physical activity. However, others are much harder to control and don’t link neatly to simple lifestyle changes.
Chronic stress, aging, heart disease, and depression have all been individually associated with increased dementia risk. New reviews of studies are suggesting they might actually be tied together.
So, what connects all these aspects? It seems to be sleep. More specifically, how sleep may assist the brain in clearing out metabolic waste that builds up while we’re awake.
“Many disorders that elevate dementia risk also disrupt sleep patterns,” says neuroscientist Maiken Nedergaard from the University of Rochester in the US.
“Our findings indicate these issues may not be separate after all; they could be linked through the brain’s waste clearance capabilities during sleep.”
Sleep is one of those great mysteries in biology. It’s crucial – lack of proper sleep leads to numerous problems.
Recent studies have even indicated it’s vital for maintaining bodily functions. For example, a 2020 study found that deadly sleep deprivation in fruit flies linked back to issues in the gut rather than the brain itself, hinting that when sleep is absent, the body’s repair systems can lag.
Nedergaard’s lab made a groundbreaking discovery over ten years ago in 2012: the glymphatic system and its roles.
Originally identified in mice and later in humans, this network is thought to facilitate the flow of cerebrospinal fluid in the brain.
Moreover, it might play a significant role in removing metabolic waste. Some researchers theorize that this system could help eliminate proteins linked to Alzheimer’s and Parkinson’s diseases.
The notion that the glymphatic system is more active during sleep has been supported by several research studies, though a notable one in 2024 found results that contradicted this, raising concerns about the relationship between sleep and the brain’s cleaning mechanisms, as well as how sleep might affect dementia risk.
Nedergaard’s review proposes a more complex picture, indicating that the quality of sleep is crucial for glymphatic efficiency.
“Sleep isn’t merely a quiet, inactive phase,” Nedergaard notes.
“During sleep, the brain engages in a specific rhythm that seems essential for its housekeeping tasks.”
She talks about a group of neuromodulators – brain chemicals such as norepinephrine, serotonin, dopamine, and acetylcholine that regulate areas like sleep, mood, and attention.
Several recent findings indicate that during non-REM sleep, these chemicals pulse together in cycles, roughly every 50 seconds.
This is important because these same chemicals can influence blood vessels.
Nedergaard suggests that in healthy sleep, this rhythm could aid blood vessels to expand and contract gently, creating waves to help move cerebrospinal fluid around in the brain.
If sleep is disrupted or influenced by drugs, that rhythm may falter, which may hinder the brain’s waste removal ability.
Consequently, chronic stress, mental health issues, cardiovascular conditions, and even age-related changes in sleep could disrupt this nighttime maintenance system.
“For years, we viewed sleep mainly through the lens of memory and restoration,” Nedergaard states.
“Now, we’re starting to see sleep as a highly organized state that transports fluids and supports brain health.”
Since our understanding of the biological reasons for sleep is still limited, it’s hard to determine if there is a causal link with dementia.
This review doesn’t resolve that question, but it does imply that the connections between sleep and overall health are inextricably linked – and understanding these links is vital for grasping a broader range of health issues, not just brain-related ones.
This overview has been published in Science.
