You Snooze, You Cruise
The Vital Role of Sleep in Brain Health.
Sleep is more than a nightly retreat – it is a fundamental pillar of health, essential for survival and optimal functioning of the body and mind. Comparable in importance to nutrition and physical activity, sleep is critical for many functions, from physical recovery to emotional regulation, and cognitive resilience.
Though we may think of sleep as a time of rest, science tells us that it is a period of high cellular activity.
During sleep, the brain consolidates memories, clears toxins, and recharges neural circuits, preparing us to tackle challenges with clarity and focus.
The benefits extend beyond the brain, influencing heart health, immune function, and overall well-being.
Despite its significance, nearly one-third of all adults suffer from sleep disturbances, which can disrupt critical processes and contribute to long-term health risks, including cardiometabolic disorders (e.g., diabetes and heart disease), cancer, accelerated brain aging, and neurodegeneration.
In their 2023 review and editorial in The Lancet, Public Health, the World Sleep Society Global Health Taskforce emphasized that the consequences of sleep deficiency are a threat to global health and the health budget of every country. Yet, sleep remains under-recognized in data collection and health policies.
CURRENT EVIDENCE SUGGESTS THAT IF SLEEP IS PRIORITIZED AS A CORE HEALTH-PROMOTING BEHAVIOUR, THIS WILL IMPROVE POPULATION HEALTH AND HELP TO ADDRESS HEALTH INEQUITIES.
STAGES OF SLEEP
Brain cells constantly communicate with each other using electrical impulses. An electroencephalogram (EEG) is a test that measures the amplitude (size) and frequency of the brain impulses and depicts them as brain waves.
Using EEG, sleep has been categorized into two phases: rapid eye movement (REM) characterized by low-amplitude and fast oscillating waves, and non-rapid eye movement (NREM) with high-amplitude and slow oscillating waves. NREM is also referred to as slow-wave sleep and is further differentiated into three stages: N1, N2, and N3.
SLEEP BOOSTS THE BRAIN
Dr. Jean-Philippe Chaput, senior scientist with the Healthy Active Living and Obesity Research Group, and a leading researcher in sleep science, highlights the range of brain health benefits of sleep:
Sleep enhances memory, protects against mental decline, and fosters emotional strength.
MEMORY CONSOLIDATION
Sleep allows the brain to process and organize information from the day. This strengthens neural connections, enhancing learning and transforming short-term memories into long-term ones.
When it comes to big decisions, it looks like the strategy of “sleeping on it” really can help you to weigh information and make informed choices!
A 2023 review in Neuron by Dr. Brodt and colleagues explained that while memory consolidation also occurs when we are awake, we are better able to synchronize neural activity with long-term memories encoded in the hippocampus part of the brain when we are asleep.
SYNCHRONIZED BRAIN ACTIVITY HELPS US TO GENERALIZE OUR EXPERIENCES FROM DIFFERENT CONTEXTS, PRODUCING STRONGER MEMORIES THAN THOSE FORMED WHEN WE ARE AWAKE.
Greater demand to integrate learning from daily experiences and form long-term memory is one of the reasons why infants require more sleep than children, and children more than adults.
TOXIN CLEARANCE
The glymphatic system, the brain’s waste-removal network, is most active during sleep. Glymphatic clearance filters harmful proteins like tau and beta-amyloid proteins out of the brain and reoxygenates the brain tissues.
A 2020 publication on the glymphatic system by Drs. Reddy and van der Werf in Brain Sciences explained there is an 80-90% increase in glymphatic clearance during the N3 stage of NREM compared to when we are awake.
The efficiency of this waste-removal system appears to decrease naturally over the course of aging, aligning with poorer sleeping patterns among older adults. This has prompted the exploration of lifestyle interventions that may be able to enhance glymphatic function, including consumption of omega-3 fatty acids, intermittent fasting, and regular exercise.
Though findings in animal model studies are promising, randomized controlled trials with humans are needed to develop clinically significant recommendations that can boost the function of the glymphatic system with age.
NEURAL PLASTICITY & EMOTIONAL REGULATION
Sleep supports neural plasticity – the brain’s ability to adapt and form new connections. This neural plasticity also helps to regulate emotions, reducing stress and anxiety.
Associations between sleep and mental health are well-established, and accumulating evidence supports a causal relationship: improved sleep significantly alleviates mental health disorders.
In 2021, Dr. Scott and colleagues published a systematic review and meta-analysis in Sleep Medicine Reviews that examined 65 randomized controlled trials with more than 8,000 participants. Findings showed that interventions to improve sleep had significant positive effects on a composite of mental health outcomes as well as separate positive effects on depression, anxiety, and stress.
Greater improvements led to greater benefits across a variety of sleep interventions and outcomes, providing strong evidence that enhancing sleep quality results in better mental health.
Future research is needed to uncover the mechanisms responsible for this causal relationship and to fine-tune the dose of various sleep characteristics necessary for mental health improvements.
SLEEP DISORDERS & BRAIN HEALTH
Sleep disorders not only disrupt nightly rest but also have long-term implications for brain health by increasing the risk of cognitive decline, emotional dysregulation, and neurodegenerative diseases.
INSOMNIA
Insomnia is when you have difficulty falling asleep or staying asleep. Chronic insomnia can impair memory, concentration, and emotional regulation. It is also associated with increased anxiety and depression.
WOMEN ARE AT A HIGHER RISK OF INSOMNIA COMPARED TO MEN, WITH HORMONAL DIFFERENCES PLAYING A ROLE.
A 2023 review by Dr. Anderson and colleagues in Frontiers in Sleep, noted that fluctuations in progesterone and estrogen are associated with sleep disruption, and among women, those with irregular menstrual cycles have twice the risk of insomnia compared to women with regular cycles.
OBSTRUCTIVE SLEEP APNEA (OSA)
OSA, characterized by repeated interruptions in breathing during sleep, reduces oxygen supply to the brain and impairs toxin clearance through the glymphatic system.
People with sleep apnea tend to spend less time in deep sleep (stage N3), and are at a higher risk of Alzheimer’s disease (AD), as well as cardiovascular problems like stroke and hypertension.
OSA APPEARS TO BE MORE COMMON IN MEN THAN IN WOMEN, WITH WIDELY VARYING ESTIMATES OF PREVALENCE IN POPULATION STUDIES.
Research suggests that female sex hormones are protective against OSA because of their role in dilating the airways, however, OSA becomes more common in women after menopause, narrowing differences between women and men.
REM SLEEP BEHAVIOUR DISORDER: AN EARLY WARNING SIGN FOR NEURODEGENERATIVE DISEASES
One sleep disorder that has garnered increasing attention is REM Sleep Behaviour Disorder (RBD). In 2023, the American Academy of Sleep Medicine published a systematic review and meta-analysis in Journal of Clinical Sleep Medicine that noted a 1% prevalence of RBD in middle to older adults, affecting approximately 80 million people worldwide. Some studies show a higher prevalence among men than women, while others report no sex differences.
RBD is characterized by acting out dreams, often through shouting, kicking, or punching during sleep. RBD occurs because the natural paralysis of the muscles during REM sleep does not work properly, allowing individuals to move their bodies in response to their dreams.
Vigorous limb movements during sleep can lead to injuries for the person with RBD and even their bed partner, making it important to create a safe sleep environment.
Research links RBD to structural changes in one part of the brainstem called the pons, a critical area for regulating REM sleep. The American Academy of Sleep Medicine explained that abnormal accumulation of a specific type of protein, known as alpha-synuclein protein, often starts in the neurons (nerve cells) of the gut and ascends through the nervous system to the REM sleep generators in the pons, compromising their function.
RBD is more than just a disruptive condition – it is an early marker of neurodegenerative diseases.
A large multi-centre cohort study published in Brain in 2019 followed patients around the world with RBD for up to 19 years. At baseline, participants were on average 66 years old and 82.5% were male. Analyses revealed that nearly 74% developed Parkinson’s disease, dementia with Lewy bodies, or another neurodegenerative syndrome within 12 years of diagnosis.
The authors suggest that RBD could serve as an important early indicator of brain health issues, making patients with RBD ideal candidates for neuroprotective trials. As well, by studying RBD patients, researchers hope to better understand the pathways that lead to neurodegenerative diseases and develop better preventive measures.
POOR SLEEP CHARACTERISTICS
We all know that it is important to get a good night’s rest, but did you know that there’s more to it than the time you spend lying in your bed? Sleep duration is just one of several sleep characteristics studied by researchers. Poor sleep characteristics include:
short sleep duration;
bad sleep quality;
difficulty initiating sleep;
difficulty maintaining sleep;
early morning awakening; and
daytime sleepiness.
Sleep disturbances are often reported during menopause, a stage linked to the decline of estrogen in women.
That 2023 review by Dr. Anderson and colleagues in Frontiers in Sleep mentioned earlier in this story, showed that 40-60% of menopausal women have trouble initiating and maintaining sleep, and experience early morning awakening.
It is possible that these sleep disturbances, particularly during
N3 deep sleep, can affect glymphatic clearance among menopausal women, placing them at higher risk of developing AD.
Sleep disturbances are also associated with sex hormones in men, with more sleep disturbances reported by men with low testosterone, and testosterone production linked to uninterrupted periods of sleep.
The Sleep Regularity Index (SRI) was developed to look at sleep and wake times measured by accelerometers, devices that detect the body’s movement. The SRI accounts for variability in several sleep characteristics like the time when someone goes to bed, how often they wake up during sleep, how long they sleep, and when they wake up.
SRI is scored on a scale from 0 (completely random sleep patterns) to 100 (perfectly regular sleep patterns) and can be used to categorize people into regular, moderately irregular, and irregular sleep patterns.
Data from a large prospective cohort study of men and women published in 2024 by Drs. Chaput and Biswas and colleagues in Journal of Epidemiology and Community Health found that irregular sleep was strongly linked to major adverse cardiovascular events like heart failure, myocardial infarction (heart attack), and stroke.
Furthermore, findings suggested that an irregular sleep schedule puts you at a higher risk of major adverse cardiovascular events even if you met sleep duration recommendations.
It may be that maintaining a regular sleep routine protects your heart health even more than getting the daily recommended 7+ hours of sleep.
POOR SLEEP & ACCELERATED BRAIN AGING
Emerging research shows that even in the absence of a sleep disorder, there may be a connection between poor sleep habits in mid-life and accelerated brain aging, putting individuals at risk of developing neurodegenerative diseases sooner.
A 2024 study in Neurology revealed that 40-year-old adults with three or more poor sleep characteristics – such as short sleep duration, poor sleep quality, or irregular sleep schedules – showed signs of advanced brain aging via MRI brain images.
Dr. Cavaillès and colleagues observed that individuals with poor sleep exhibited brains that were 2.6 years older than those with healthier sleep patterns!
THESE FINDINGS SUGGEST THAT MID-LIFE IS A GOOD TIME TO SET DOWN HEALTHY HABITS THAT IMPROVE SLEEP AND PRESERVE YOUR BRAIN HEALTH.
Sleep is a powerful, yet often overlooked, ally in maintaining brain health. By prioritizing good sleep habits, we can enhance cognitive performance, reduce the risk of neurodegeneration, and enjoy a healthier, more resilient mind.
As Dr. Chaput summarized, “A brain that gets quality and regular sleep functions more effectively, fuelling creativity, improving focus, and safeguarding memories.”
Source: Mind Over Matter V20