Dr. Barry Jarvis
Sleep is vital for physical health, brain function, emotional regulation, memory, and so much more. But not all sleep is equal in terms of restorative benefits. The most critical part of our sleep is “core sleep” – comprised of the deep, rejuvenating stages.
Understanding the different cycles and stages of core sleep versus light sleep can help you optimize your slumber to feel energized, mentally sharp, and emotionally balanced daily.
In this comprehensive guide, we’ll explain what core sleep is, what stages and cycles comprise it, and why it’s the most important sleep for feeling refreshed and operating at your best during the day.
What Is Core Sleep?
Core sleep refers to the critically restorative stages of deep non-REM and REM sleep that allow true physical and mental rejuvenation.
It is sometimes also called “slow wave sleep” since it is characterized by slow brain waves. Core sleep stands in contrast to light non-REM sleep.
During core sleep stages, our body carries out crucial processes like:
- Tissue growth and repair
- Energy restoration
- Immune system strengthening
- Memory consolidation
- Emotional regulation
Without sufficient core sleep, we wake feeling groggy no matter how long we’ve slept. Getting adequate core sleep is essential for optimal daily performance – both mental and physical.
Now let’s explore exactly what comprises core sleep and its distinct stages.
The Stages of Human Sleep
There are two main types of sleep:
Non-REM sleep – Our brain and body cycle through lighter to deeper non-REM sleep stages.
REM sleep – REM brings vivid dreaming as our brain becomes active but our body remains paralyzed.
Within non-REM, scientists categorize 3 stages ranging from lightest to deepest:
Stage 1 Non-REM – The lightest sleep and transition from wakefulness. Easy to disrupt.
Stage 2 Non-REM – Still light but with periods of muscle/brain relaxation.
Stage 3 Non-REM – The deep, slow wave core sleep rejuvenating the body.
REM sleep is its own unique stage, cycling with non-REM throughout the night.
Let’s look at how core sleep fits within these stages and cycles.
Core Sleep Comprises Deep Non-REM and REM
Not all sleep stages provide the same restorative benefits. The most critical rejuvenating sleep occurs during:
Slow wave deep non-REM (Stage 3 NREM) – The deepest phase of human sleep. Brain waves are extremely slow as the mind and body recharge. This allows tissue growth and repair.
REM sleep – Vivid dreams occur as the brain becomes active in REM but muscles stay paralyzed. REM supports emotional regulation and memory consolidation.
Together, deep slow wave NREM combined with REM form what is considered core sleep where the most transformative restoration takes place both physically and mentally.
The lighter stages 1 and 2 non-REM are not considered core sleep. While better than no sleep, light sleep does not provide the same recuperative advantages.
Now let’s dive deeper into deep NREM and REM to understand why they are so essential.
Slow Wave Deep Non-REM Sleep
During deep non-REM, our heartbeat and breathing slow while brain waves become long and extremely slow. This facilitates complete mind/body restoration.
Here are the key benefits occurring during deep sleep:
Cellular Repair and Growth
Deep NREM triggers the release of human growth hormone which repairs muscles and tissues. Without enough deep sleep, the body can’t fully regenerate on a cellular level.
Immune System Strengthening
Deep sleep allows white blood cell production to ramp up. This boosts immune function so you resist infection and stay healthy.
Brain Detox
Cerebrospinal fluid flows rapidly during deep sleep to wash away neurotoxic waste buildup from the brain leaving you mentally sharp.
Energy Restoration
Slow wave sleep allows metabolic processes like glucose production to restore energy stores for the body and brain to function optimally.
Clearly deep non-REM sleep provides incredible rejuvenation effects. Without enough we suffer both physically and cognitively.
Next let’s explore the magic of REM sleep.
REM Sleep Benefits
When REM was first discovered in the 1950s, researchers described it as a “paradoxical state of sleep with characteristics remarkably different from the usual ones.”
Here are some ways REM provides its own unique restoration:
Emotional Regulation
REM helps process and consolidate emotional experiences from the day. Missing REM is linked to emotional volatility, anxiety, and depression.
Memory Processing
The hippocampus replays memories and learnings during REM to transfer them from short to long-term storage. Lack of REM hampers learning.
Creative Problem-Solving
REM increases communication between the right and left brain hemispheres. This cross-talk fuels creative insights and new perspectives on problems.
Healthy Nervous System
REM triggers protein production needed for maintaining and building new neural connections. This keeps the nervous system thriving.
Clearly both non-REM deep sleep and REM sleep serve complementary purposes that keep our minds and bodies humming.
Ideal Sleep Architecture: The Right Mix of Stages
Now that we understand the different sleep stages, what mix of light sleep, deep sleep, and REM is considered ideal nightly?
Research indicates the optimal sleep architecture includes:
- 10-30% in Stage 1 light sleep
- 40-60% in Stage 2 light sleep
- 15-25% in deep slow wave non-REM
- 20-25% in REM sleep
Adults should aim to spend at least 85 minutes in deep NREM and 90 minutes in REM per night. Older adults benefit from even more slow wave deep sleep given reduced sleep efficiency.
Ideally we seamlessly cycle between light, deep and REM sleep 4-6 times over a 7-9 hour sleep period as illustrated below:
Chart source: Wikimedia Commons
Without sufficient core non-REM and REM, we awaken feeling unrested no matter our total sleep duration. Optimizing those critical sleep stages results in higher energy, better concentration, improved mood, and reduced disease risks.
How Much Core Sleep Do Adults Need?
The American Academy of Sleep Medicine and the Sleep Research Society recommend adults get a minimum of 7 hours nightly to maintain optimal health and performance.
Within those 7 hours, they further recommend:
- At least 85 minutes of deep non-REM sleep
- At least 60 minutes of REM sleep
That equates to getting roughly 2 full 90-120 minute sleep cycles including both deep and REM.
However, individual differences in sleep needs vary. Some feel their best with a consistent 8-9 hours embracing 3 full cycles nightly of core sleep stages.
The key isn’t total sleep duration. It’s prioritizing those essential deep NREM and REM cycles in the time you allot for sleep. Nailing consistent, high-quality core sleep is what matters most.
Why Is Core Sleep So Important?
We’ve touched on many of the benefits like tissue repair, memory consolidation, energy restoration and emotional regulation that occur during core non-REM and REM sleep.
But why is core sleep so much more restorative than lighter sleep stages? Here are some of the key reasons:
Metabolic Changes
Deep sleep triggers a metabolic shift resulting in reduced body temperature, breathing rate, oxygen usage and heart rate. This facilitates cellular restoration.
Neural Oscillations
The synchronized neural oscillations between brain regions during deep sleep are critical for memory, learning and cognition.
Memory Consolidation
Deep sleep clears and consolidates short term memories while REM transfers them to long term storage. Light sleep provides minimal memory benefit.
Hormone Release
Vital hormones like human growth hormone and prolactin are secreted primarily during deep and REM to drive cellular repair, immune function and bone growth while we sleep.
Reduced Cortisol
Core sleep stages lower cortisol, the stress hormone. Light sleep provides smaller reductions in cortisol, resulting in less stress relief.
As you can see, core sleep delivers a host of mind/body benefits unmatched by lighter sleep. Prioritizing your inner clock to maximize time in restorative stages is key to feeling refreshed.
Tips to Maximize Core Sleep
Looking to optimize your core sleep amounts? Here are some tips:
Maintain consistency – Keep a fixed sleep schedule, even weekends, to sync your circadian rhythm.
Limit alcohol – Drinking close to bed disrupts non-REM and REM cycles all night. Have your last drink 3+ hours before bed.
Avoid sleeping pills – Many sedatives reduce time spent in deep and REM sleep.
Cut out nighttime distractions – Light, noise, pets and an uncomfortable mattress all impair deep sleep.
Manage stress – Anxiety and rumination make it hard to relax into deep NREM.
Check your supplements – Some supplements like melatonin may reduce REM sleep.
Exercise earlier in the day – Exercising too close to bed makes it harder to wind down.
Skip late snacks – Finish eating 2-3 hours pre-bed to optimize sleep hormone release.
Adjusting these lifestyle factors can help you maximize time spent in the most restorative core sleep stages.
Signs You’re Not Getting Enough Core Sleep
How can you tell if you’re not spending sufficient time in deep non-REM and REM sleep? Signs include:
- Needs an alarm to wake up
- Difficulty waking up
- Excessive grogginess upon waking
- Fatigue persisting throughout the day
- Impaired concentration, memory and reaction time
- Increased clumsiness and accidents
- Reduced motivation and mood
- Sugar and carb cravings
- Increased pain sensitivity
- Frequent sickness and infections
- Skin issues and bags under eyes
Pay attention to these signs your body may be starved of rejuvenating core sleep.
Optimizing Your Core Sleep With Sleep Tracking
Wondering how much core sleep you’re actually getting? Sleep tracking provides insight.
Devices like the Óura ring, Fitbit trackers, or Beddr sleep sensor can monitor your sleep cycles and stages all night by tracking metrics like:
- Heart rate variability
- Body temperature
- Respiratory rate
- Oxygen levels
- Movement
Apps then provide breakdowns showing your time in light, deep and REM sleep.
Track your sleep quality for 2 weeks using these devices. Try to optimize your sleep environment and habits naturally to increase your deep and REM sleep amounts.
If you continue having low core sleep, speak to your doctor or a sleep medicine specialist for additional guidance.
The Takeaway On Core Sleep
Core sleep comprising deep non-REM and REM stages provides the true mental and physical rejuvenation benefits allowing us to function optimally.
Prioritize consistency, minimize disruptions around bedtime, and practice good sleep hygiene to maximize your time spent cycling through light sleep into those essential deep and REM stages nightly.
Quality over quantity applies when it comes to sleep. Focus on optimizing the aspects of core sleep to wake up feeling restored and thriving every day.
FAQs About Core Sleep
What are the 4 stages of sleep?
The four stages of sleep are: Stage 1 light sleep, Stage 2 light sleep, Stage 3 deep slow-wave sleep, and REM sleep. Stages 3 and REM comprise “core” sleep.
Why is deep sleep more important than light sleep?
Deep non-REM sleep triggers growth hormone release, immune strengthening, tissue repair, brain detox and energy restoration. Light sleep does not provide the same whole-body rejuvenation.
Is REM or deep sleep more important?
REM and deep non-REM play complementary roles. Deep sleep restores the body physically while REM impacts emotional regulation and memory function. Both are critical for feeling well rested.
How can I get more deep sleep?
Maximize deep sleep by avoiding alcohol before bed, reducing screen time, maintaining a cool room temperature, sticking to a consistent bedtime, exercising earlier in the day, and managing stress.
How much deep sleep should I get?
Most adults need about 15-25% of total sleep time in the deep non-REM stage to reap its full restorative benefits. That equates to around 85-100 minutes over 7-9 hours.
How can I tell if I’m getting good core sleep?
Track your sleep with a device like Fitbit or Oura ring. If you wake feeling refreshed with enough energy to perform both physically and mentally without needing to snooze, it’s a sign you’re getting sufficient high-quality core sleep.
Prioritizing those essential stages of core non-REM and REM sleep transforms how you feel and function daily. Use these insights to optimize your bedtime routine and habits so you secure consistent, restorative sleep.
Originally posted on September 18, 2023 @ 6:19 am
Author
Dr. Barry Jarvis
Dr. Barry Jarvis is a renowned sleep specialist, dedicating their illustrious career to the intricate world of sleep medicine. Holding a medical degree from a prestigious institution, Dr. Jarvis has cultivated a deep understanding of the complex mechanisms that govern sleep and its pivotal role in overall health and well-being. With a compassionate approach and a meticulous eye for detail, Dr. Jarvis has helped countless individuals reclaim restful nights and vibrant days. Beyond their clinical expertise, they have contributed to groundbreaking research in sleep medicine, unraveling the mysteries of sleep disorders and pioneering innovative treatments that stand at the forefront of the field.
