read time: 10 minutes.
sleep + stress: part I.
table of contents.
- maladaptive resource allocation of chronic stress
- broad term that defines the consequences of long term stress
- focus on sleep + stress
- minimizing stress and maintaining appropriate sleep architecture is critical for a well-oiled, healthy functioning body and optimal mind.
- why we sleep
- neurotransmitter activity
- conserve energy resources
- repair and rejuvenate
- brain plasticity
- memory, mood + emotion modulation
- circadian rhythm
- what is it?
- the processes it effects
- sleep/wake cycle
- cognitive function
- effects of stress on sleep
- circadian rhythm becomes off
- time it takes to fall asleep and stay asleep
- interrupted sleep cycle (waking up mid-sleep)
- disrupts deep sleep or rem sleep
- biological effects (deprivation or poor sleep)
- brain fog
- glymphatic system
- suppressed immune system
- lower defenses (cytokines to infections)
- higher risk of short term and chronic illness
- increase in inflammatory cytokines
- increased cortisol/ caffeine and adenosine
- stimulates and keeps you alert
- pattern t/o the day (biorhythm)
- inconsistent sleep schedules
- combat stress and support healthy sleep hygiene
- healthy diet and hydration
- healthy stress
- minimizing stressors
- allowing your body to rest and digest when needed
- improve your sleep environment
- comfort (mattress)
- create a space for sleep and only sleep
the witching hour has arrived. your eyelids shoot open as you roll over to click the home button on your phone - 3:20 am. just as you expected. an internal sigh of exasperation. time to take the next hour or two trying to figure out how to get back to sleep.
with the constant stimulation each day brings, daily stressors have become permanent guests. some we are so accustomed to that we may not even recognize the impact they have on our minds and bodies. the daily grind has most of us in a state of perpetual fight or flight (fof), pushing us to the limit and keeping the sympathetic nervous system on high. so instead of managing a stress-adapting, healthy ship, valuable resources are being diverted to produce energy to keep the ship in battle mode. this maladaptive resource allocation leads to chronic stress and its countless consequences.
lack of quality sleep is very common and often the result of high nervous system tension being carried into the evening as a result of chronic, imbalanced stress. 65% of americans report getting less than 6 hours of sleep/night, which reliably predicts increased risk of all-cause mortality.
let’s get into it.
why we sleep.
we’re going to start with the basic concept of: why we sleep.
this topic is one that has baffled scientists for years, and there isn’t exactly a clear-cut, 1-off answer to this question. however, there are some pretty good collective theories that we know are on the right path.
as animals, our bodies have evolved to be on what is called the circadian rhythm (more on this in a bit). this rhythm has us up and about during the light hours, and down for the count during the darker hours.
during sleep, we see highly important, can’t-live-without processes taking place. some of these biological functions include an increase in glymphatic functioning, rest and ramp-up of neurotransmitter action, protein synthesis, detoxification, and tissue repair. however, in order for some of these processes to take place, our brains and bodies have to reach certain stages in our sleep cycle.
due to the fragility of this cycle (there are many internal and external factors that have to line up) many people are not getting adequate amounts of each stage.
you might notice this when you think you get enough sleep, but still feel as though your energy and concentration are lacking. this is often the consequence of not getting adequate stage 3 deep sleep.
there’s a fine line when it comes to maintaining a healthy sleep cycle. in order to best explain, we're going to break it down stage by stage.
stages of the sleep cycle.
during the sleep cycle, we go through different stages of non-rapid eye movement sleep (nrem) and rapid eye movement sleep (rem). together, they create a cycle of about 90 minutes - each stage making up 25% of the cycle (varying throughout the night and from person to person). a healthy amount of sleep consists of about 6 cycles in 8-9 hours.
rem is the fourth stage of sleep, where we get our deepest, quality sleep, and where we dream. this is also where areas of our brain are stimulated into processing new information and retaining memories. nrem is broken up into three different stages, the third (n3) is where deep sleep begins.
in the beginning of the night, adult brains start off getting the least amount of rem sleep, but as the night progresses, rem begins to grow and n3 starts to sacrifice its time.
since we see the most significant biological functions taking place in these two stages, and since there is only a certain amount of time spent in each crucial stage, prioritizing deep sleep is important.
as we delve into stages n3 and rem, the reasons behind making them a priority start to unfold. we’ll start off with how sleep encourages energy conservation.
energy conservation support.
introducing: glycogen, adenosine and cortisol. three energy-related compounds.
glycogen is a product of broken-down glucose molecules. these molecules play a critical role in storing energy in the brain. during waking hours, as we expend energy we see a decrease in glycogen levels. however, when we rest and reach levels n3 and rem of our sleep cycles, those glycogen stores start to increase as they prepare our brains for an energetic next day. when it comes to adenosine, we see the opposite effect.
adenosine is a product of a broken-down molecule called adenosine triphosphate (atp). this is a molecule that neurons in the brain break down for energy. throughout the day, more and more adenosine accumulates and attaches to receptors letting the brain know that it has burned through lots of energy and needs to take a rest.
think: lots of adenosine = sleepy brain.
while we are in deep sleep, the body clears out the excess adenosine and we are able to wake up the next day raring and ready to go.
this chemical dance between adenosine and glycogen is one of many that makes up what we call sleep homeostasis. during sleep, we see our bodies conserving energy by decreasing the use of costly processes like respiration, heart rate, and muscle mobility. as we reduce the energy used for these systems, we're able to allocate that energy towards important processes that take place during sleep homeostasis!
we’re talking about replenishing those glycogen stores and boosting immune function. all because we decided to make a true commitment to sleep.
introducing: cortisol + melatonin.
cortisol, the hormone keeping us alert during the day (and released during fof), is at its peak levels in the morning. these high levels of cortisol occur due to a drop off of melatonin (the sleep hormone). towards the end of the day cortisol levels start to drop off, stimulating melatonin secretion and winding our alertness down. this is part of our circadian rhythm.
think: cortisol during the day to keep us grinding. melatonin towards the evening to put us to sleep.
unfortunately, if stress creeps into the evening, keeping cortisol levels high, melatonin will continue to remain low. this influences your ability to fall asleep and in turn, decreases sleep quality.
the last conservation effort we are going to discuss is the turning off of certain neurotransmitters in the brain during nrem, in order to regain their sensitivity during the waking state. some of these neurotransmitters include norepinephrine, serotonin and histamine which are involved with alertness and mood modulation. norepinephrine is also directly correlated to the glymphatic system (which we will touch more on in a bit).
repair and rejuvenate.
another reason why we snooze is to allow our systems to repair and rejuvenate. since we go pretty hard day to day, when we are finally able to rest this is the time for our systems to do some analysis and damage control.
we’re human... we’re bound to push the envelope, it’s how we become better each day. sleep is that friend that lays us down and tells us to take a beat so anything that needs fixing and refilling can be done.
muscle growth, tissue repair, protein synthesis, etc. are all a part of the physiological ‘repair and rejuvenate’ process. sleeping is their moment to shine, and during n3 and rem is where we see many of these crucial processes taking place. one of the major rejuvenation moments for our brains was that ballet we just mentioned between adenosine and glycogen.
along with adenosine activity in the brain, scientists are finding that the phenomenon of brain plasticity and sleep are connected. brain plasticity is about brain growth and reorganization, and neurons having the opportunity to make new pathways and connections. all so that we can continue to learn new abilities and keep our cognitive functioning sharp. in order to make these processes successful, we give a huge shout-out to neural connections called synapses. when we learn new skills, the data in our short-term memory triggers our synapses to shift and change.
the longer we practice and use this information, the stronger the synapses become. this is all largely happening while we are in the stage of rem sleep. and as previously mentioned, our brains have to venture through those first three stages of nrem (about 75% of the cycle) in order to achieve the rem stage (the last 25%). it’s a journey.
while we’re on our way to rem, stopping in n3 is highly important.
many of you have heard of our body’s lymphatic system, the system that is part of our immune system and the highway for white blood cells. we now give you: the glymphatic system.
this system works tirelessly during n3 to increase cerebrospinal fluid (csf) flow and clear out any toxic cellular trash that has built up in the brain.
when the brain isn’t able to take out the garbage, we see build-up of metabolites like amyloid-beta (a by-product of a protein that supports synapse formation and neural plasticity).
amyloid-beta is considered plaque and is directly linked to neurodegenerative diseases like alzheimer's.
further, looking back on our inhibition of neurotransmitters, the decline of norepinephrine is directly responsible for the increase of interstitial space in the brain. without the turning off of these neurotransmitters, there would be no increase in csf and therefore no clearance of toxic waste.
there are consequences when n3 doesn’t thrive throughout the night.
onto our circadian rhythms.
as mentioned, these rhythms are our internal clock systems and are a result of evolution. for human beings, they function on a 24-hour, light-dark cycle using cues from the environment (sunset) to nudge our bodies into the appropriate action (sleep time).
however, this is a rather simplistic view as our circadian rhythms carry much more weight than simply telling us when it is time to lay our heads down.
internally, as our rhythms trigger sleep, they, in turn, trigger the biological processes mentioned above - sort of like a domino effect.
this leads to more of that groggy and tired feeling when you know you got that 8+ hours of sleep. stress is a major culprit of keeping nervous tension high throughout the evening and causing a rift in the circadian rhythm.
when stress is triggered in the body, the response prioritizes short-term survival over long-term health. your brain reacts by keeping you in the lighter stages of sleep just in case you need to be alert for any potential threats.
think about sleeping in an unfamiliar place, like a hotel room. did you get a “restful” night of sleep, but still feel the grogg we mentioned earlier? that’s because the brain did what it has evolved to do, and was on watch for most of the night.
if you’re not productively balancing the inevitable stress in your daily life, you’re probably carrying higher tension into the evening on a regular basis and throwing off the sleep cycles. this means you're not getting optimal sleep on a regular basis which will negatively impact all health and performance, mental and physical.
so the conclusion is, in order to be functioning and performing at our peak capacity, we want good, restful, uninterrupted sleep. unfortunately, with the way chronic stress rules over many of us these days, that quality sleep we just put on a pedestal is not always, or never an option.
our next piece on sleep and stress dives into why quality sleep can be hard to come by, and what you can do to reach your dream sleep goals.
the circadian rhythm is a biological clock that responds to internal + external cues and regulates the human sleep-wake cycle. during this cycle, there are physical, mental, and behavioral changes that occur. this entire cycle is roughly 24 hours.
starting in the morning, there is an increase in the hormone cortisol which causes alertness. when cortisol is released, melatonin (sleep hormone) is inhibited. there is an increase in blood pressure first thing in the morning and heart rate, respiration and digestion ramp up from lower levels during sleep.
throughout the day alertness, coordination, reaction time and body temperature increase as the body burns through atp energy molecules. when atp is broken down by the brain, the by-product adenosine builds up and fits into receptors that let the brain know it is getting tired from burning energy. the more atp used→ the more adenosine builds up→ the more tired you become. this usually happens around the late afternoon/evening when the body is also getting external cues from the sun that it is time to wind down.
once the eyes stop receiving blue light from the sun, there is no longer inhibition of melatonin and the hormone begins to release. melatonin secretion gradually increases right after darkness, reaching a peak in the middle of the night (around 2am-4am). from there, melatonin begins to decrease up until the release of morning cortisol.
during sleep, the body reaches its lowest temperature, blood pressure, heart and respiration rate. brain activity slows down at the beginning stages of sleep and spikes during rem stage. brain plasticity and the immune system are highly active during sleep hours.
humans have evolved to sleep as it is a way for the body and brain to repair, rejuvenate and conserve energy. this evolution has been fine-tuned over thousands of years so that the human species can survive and thrive at peak capacity.
a unique system in the brain that uses specialized tunnels, called perivascular tunnels or space, cerebrospinal fluid (csf) and interstitial fluid to clear out neurotoxic waste products that build up in the brain. this system is the most active during the third stage of nrem sleep (n3) and is mostly inactive during waking hours. when the body and brain reach n3, the flow of fluid increases from 15%-24% and clearance of waste is expedited. without significant time spent in n3, the glymphatic system is unable to take out the cellular garbage and *neurodegenerative diseases can ensue.
*research shows that the glymphatic system is responsible for clearing our metabolite plaque such as aamyloid-beta, which is responsible for the neurodegenerative disease alzheimer’s.
maladaptive resource allocation.
the body's process in which valuable energy resources are diverted away from crucial biological processes (immune system, digestion, detoxification, neurogenesis, etc.) in order to fuel the fight-or-flight response that is triggered by the sympathetic nervous system. maladaptive resource allocation happens over time when the body and brain are chronically stressed as energy is consistently being utilized to support processes like increased heart rate and breathing, muscle strength, heightened vision, and a shift towards the instinctive, reactive part of the brain. over time, there is massive imbalance in the body as homeostasis is constantly being disrupted by the stress response
stages of sleep.
when we sleep, we go through stages. we then go through cycles of all the stages. nrem1→ nrem2→ nrem3 → rem. this cycle is repeated around six times per night and lasts about 90 minutes. although on average, each stage consists of 25% of the cycle, it does vary throughout the night. 8-9 hours of these cycles is considered the optimal amount of sleep, however, it should be noted that it is necessary to get a quality amount of certain stages (3+4) in order to feel rested and ready to go. below are the names of the stages and what is happening to the body and mind when we go through each stage.
non-rapid eye movement stage 1 (nrem 1): doze off stage. there might be some twitching as the muscles relax. the brain and body functions, as well as eye movements, begin to slow down. brain waves also begin to slow down in comparison to the active patterns during the day.
non-rapid eye movement stage 2 (nrem 2): light sleep stage. brain, body, and muscles start to slow down and relax even further. eye movement slows, then stops and the body’s temperature begins to drop. brain waves are even slower than in nrem 1, marked by larger brief pulses leftover from daytime activity.
non-rapid eye movement stage 3 (nrem 3): deep sleep stage. it is almost impossible to wake someone up in this phase. heartbeat and breathing are at their slowest and there is no eye movement. brainwaves are the longest and slowest in comparison to other stages. as to reasons why we sleep, many of them happen in this phase.
in the brain, specific neurotransmitters are turned off (norepinephrine, serotonin, and histamine) so that they are able to regain sensitivity and work at peak capacity during waking hours. the temporary retirement of norepinephrine triggers the glymphatic system to go into action. the glymphatic system is the brain's waste removal system. it clears out any toxic waste that has accumulated during the day, including adenosine, a byproduct of atp (energy molecule). adenosine builds up throughout the day and lets the brain know it’s burned through lots of energy and is now tired. in order to feel clear-headed, these adenosine molecules need to be cleared out and the glymphatic system is the one to do it!
elsewhere in the body, the immune system is getting a boost. integrin production increases. these are proteins that provide t-cells (adaptive immune system fighters) with their stickiness to latch onto invaders. without nrem3, t-cells lose much of their ability to attach to and eliminate unwanted foreign molecules. due to the boost during this stage, tissues and muscles are also receiving extra attention for repair. whether you’ve been working out or have an injury, nrem3 is when those repairs are attended to.
nrem3 is the hardest stage to consistently get as many factors can prevent the body and brain from entering this stage. take sleeping in a hotel room for example. the brain is aware that you are in an unknown space, and due to the evolution of survival, the brain needs to be on alert just in case there’s a threat. since nrem3 is the deepest sleep (and near impossible to wake someone up from), the brain chooses to not spend as much time in this stage.
a couple more examples include coffee and artificial blue light. both of these are mechanisms that prevent sleep triggers from occurring in the brain. with the delay of sleep triggers, the sleep cycles get pushed back and we aren’t able to spend the time we need in the important stages (nrem3 and rem). without quality time spent in these stages, the biological processes mentioned above occur less, which in turn causes detrimental consequences to our overall health.
- cdc. (2020). module 2. sleep and the immune system. centers for disease control and prevention. retrieved from: https://www.cdc.gov/niosh/work-hour-training-for-nurses/longhours/mod2/05.html.
- rodnitzky, r. l., tranel, d., & cooper, g. (2003). higher brain functions . higher brain functions. retrieved from: https://link.springer.com/chapter/10.1007%2f978-1-59259-371-2_29
- tosini, g., ferguson, i., & tsubota, k. (2016). effects of blue light on the circadian system and eye physiology. molecular vision. retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/pmc4734149/.
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