The Importance of REM and Deep Sleep and How to Improve Them
Updated: Sep 19
Written by Dr Saneka Chakravarty, MD, FACC. Dr Chakravarty is a board-certified cardiovascular disease specialist focused on personalized preventive cardiovascular care.
Getting a full night's rest isn't just about how long you sleep, it's about how well you move through your sleep stages. Two of the most important stages for your health are REM (rapid eye movement) sleep and deep sleep (also called slow-wave sleep, or SWS). Each supports the brain and body in distinct ways, from memory and mood to physical repair.
Here's what the science actually says about these stages and what you can realistically do to improve them.
What Is REM Sleep?
REM sleep is a mentally active stage that recurs in cycles across the night, growing longer with each cycle toward morning. It's when most vivid dreaming occurs, and it's marked by rapid eye movements, near-complete muscle relaxation (atonia), and fast, wake-like brain activity.
Why REM sleep matters:
Emotional processing and mood. REM sleep helps regulate emotional reactivity by rebalancing activity between the brain's emotional (limbic) and regulatory (prefrontal) regions. Sleep loss and disrupted REM in particular, is linked to heightened emotional reactivity, anxiety, and depression (Tempesta et al., Sleep Medicine Reviews, 2018; Perogamvros et al., Frontiers in Psychology, 2013).
Memory consolidation. REM sleep is implicated in synaptic plasticity, neural reorganization, and the consolidation of emotional and procedural (skill-based) memories, though its precise role in fact-based learning is still debated (Ayati et al., Scientific Reports, 2026; Pérez-Carbonell & Iranzo, Current Neurology and Neuroscience Reports, 2023).
Creativity and flexible thinking. REM has long been associated with novel associations and creative insight. It's worth noting that much of this evidence comes from studies that deprived people of REM rather than enhanced it, so the link is real but not fully settled (Elliott et al., Journal of Psychopharmacology, 2025).
What Is Deep Sleep (Slow-Wave Sleep)?
Deep sleep, or N3, dominates the first half of the night. It's defined by large, slow "delta" brain waves, along with reduced heart rate, breathing, and blood pressure , the most physically restorative stage.
Why deep sleep matters:
Memory stabilization. Slow-wave sleep is central to consolidating declarative (fact-based) memories. During this stage, coordinated slow oscillations, sleep spindles, and hippocampal "ripples" help transfer memories from the hippocampus to long-term cortical storage (Pérez-Carbonell & Iranzo, Current Neurology and Neuroscience Reports, 2023; Cairney et al., Current Biology, 2018).
Physical recovery and immune health. Growth hormone release, tissue repair, and immune restoration are concentrated in deep sleep.
Brain waste clearance. During slow-wave sleep, the brain's glymphatic system flushes metabolic waste . including beta-amyloid and tau, most efficiently. This clearance is strongly associated with N3 sleep; whether improving it directly lowers Alzheimer's risk is a promising hypothesis still under active study, not a settled fact (Xu et al., Molecular Psychiatry, 2026; Gottesman et al., AHA Scientific Statement, Circulation, 2024).
REM vs. Deep Sleep at a Glance
Feature | REM Sleep | Deep Sleep (SWS/N3) |
Brain waves | Fast, wake-like | Slow, high-amplitude delta |
When it occurs | More in the second half of the night | More in the first half of the night |
Key functions | Emotional processing, procedural memory, creativity | Fact-based memory, physical repair, waste clearance |
Share of total sleep | ~20–25% | ~13–23% |
Science-Backed Ways to Improve REM and Deep Sleep
1. Keep a consistent sleep schedule. Going to bed and waking at the same times supports circadian alignment and lets you complete full sleep cycles, protecting both REM and deep sleep (Wang et al., PLoS One, 2025).
2. Limit caffeine and alcohol. Caffeine blocks adenosine (the chemical that builds sleep pressure), delaying sleep and reducing deep slow-wave sleep, effects that can persist even when caffeine is taken only earlier in the day. Alcohol may speed sleep onset but suppresses REM early and fragments sleep later in the night (Weibel et al., Scientific Reports, 2021; Badin et al., Current Psychiatry Reports, 2016; Song & Walker, PLoS One, 2023).
3. Get morning light. Early daylight anchors your circadian rhythm, which governs the timing of REM and overall sleep quality (Bishop et al., Sports Medicine, 2025).
4. Wind down without screens. Evening blue light suppresses melatonin and can delay sleep. Swap screens for reading, stretching, or a warm bath (Jiang-Xie et al., Neuron, 2025).
5. Try relaxation rituals. Mindfulness meditation, relaxation techniques, and CBT-based approaches improve sleep quality and support cognitive function and are recommended as first-line for ongoing sleep problems (Siette et al., Scientific Reports, 2025).
6. Move your body, ideally earlier in the day. Regular physical activity builds sleep drive and can support REM sleep and heart-rate variability; morning exercise appears especially favorable, while vigorous late-evening exercise may disrupt sleep in some people (Wang et al., PLoS One, 2025).
A Note on "Sleep Hacks"
Techniques like targeted memory reactivation (TMR), replaying subtle sound cues during sleep to strengthen specific memories are a genuine area of research, but they belong in sleep labs, not bedrooms. Importantly, TMR works during deep NREM sleep, not during REM: a meta-analysis of 91 experiments found reliable memory benefits during stage 2 and slow-wave sleep, with no effect during REM or wakefulness (Hu et al., Psychological Bulletin, 2020).
Frequently Asked Questions
How much REM and deep sleep do I need? Most healthy adults need 7–9 hours total. That typically works out to roughly 1.5–2 hours of REM and about 1–2 hours of deep sleep, though the exact amounts vary by age and individual, deep sleep in particular declines with age.
Can I "make up" lost REM or deep sleep? Partly. After deprivation, the body tends to "rebound" by spending more time in the missed stage on subsequent nights. But chronic sleep loss accumulates costs that a weekend of catch-up sleep cannot fully reverse.
Are consumer sleep trackers accurate? They're useful for spotting trends but imperfect. Most estimate sleep stages from movement and heart rate and are considerably less accurate than medical-grade polysomnography, especially for distinguishing specific stages.
Should I take melatonin? Melatonin mainly helps shift circadian timing (for example, in jet lag or delayed sleep phase). It does not reliably boost REM or deep sleep and is best used at low doses and under clinician guidance.
When should I see a doctor?Persistent trouble falling or staying asleep, loud snoring with gasping or witnessed pauses in breathing, or daytime sleepiness that affects functioning all warrant evaluation: these can signal insomnia or obstructive sleep apnea, which are treatable.
This handout is for general education and is not a substitute for individualized medical advice.
See how we incorporate sleep metrics into our clinical evaluation at https://www.preventiononly.com/theapp
References
Promoting Memory Consolidation During Sleep: A Meta-Analysis of Targeted Memory Reactivation. Hu X, Cheng LY, Chiu MH, Paller KA. Psychological Bulletin. 2020;146(3):218-244. doi:10.1037/bul0000223.
Sleep-Related Changes Prior to Cognitive Dysfunction. Pérez-Carbonell L, Iranzo A. Current Neurology and Neuroscience Reports. 2023;23(4):177-183. doi:10.1007/s11910-023-01258-2.
The glymphatic system in sleep: a nexus of waste clearance, brain homeostasis, and disease intervention. Xu Y, Huang W, Jiang X, Fan Y, Bian Q. Molecular Psychiatry. 2026;:10.1038/s41380-026-03750-w. doi:10.1038/s41380-026-03750-w.
Impact of Sleep Disorders and Disturbed Sleep on Brain Health: A Scientific Statement From the American Heart Association. Gottesman RF, Lutsey PL, Benveniste H, et al. Stroke. 2024;55(3):e61-e76. doi:10.1161/STR.0000000000000453.
Imperatorin restores behavioral and recognition memory deficits induced by REM sleep deprivation in male rats. Ayati MM, Eslami M, Yekta BG. Scientific Reports. 2026;16(1):24610. doi:10.1038/s41598-026-49071-4.
The impact of daily caffeine intake on nighttime sleep in young adult men. Weibel J, Lin YS, Landolt HP, et al. Scientific Reports. 2021;11(1):4668. doi:10.1038/s41598-021-84088-x.
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Effectiveness of behavioural sleep programs for middle-aged adults on cognition and sleep and associated behaviour change techniques: a systematic review and meta-analysis. Siette J, de Vera-Pinpin MJR, Alsager SY, et al. Scientific Reports. 2025;15(1):40448. doi:10.1038/s41598-025-24009-4.
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