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37 FACTORS · 5 CATEGORIES · PEER-REVIEWED
What actually influences your REM sleep?
REM is the stage tied to dreaming, emotional processing, and memory — and it's unusually sensitive to chemistry and body temperature. We dug into the research on what really moves dream sleep, ranked by evidence strength. Here's what helps, what hurts, and what's just hype.
REM is defended
peer-reviewed
140%
of baseline REM on the first recovery night after REM loss — your brain pays back its dream-sleep debt automatically.
Endo et al. 1998
37
Factors analyzed
37
Peer-reviewed sources
5
Categories of influence
−11
min
Alcohol's nightly hit to REM
Start here
Quick answers.
Our top picks, ranked on evidence strength and practical impact. Tap any to expand.
Best Lever You Control
Sleep Longer
Key Stat: 4 h vs 9 h: REM cut first
REM is back-loaded into the early morning, so a short night with a fixed alarm cuts dream sleep before any other stage. Protect the back half of the night.
Category: Environment & Habits
Quickest Environmental Win
Keep the Room Cool
Key Stat: 32°C vs 22°C: less REM
A 32°C bedroom lowered REM vs 22°C, and a cooling topper restored it. Cool protects REM, but going colder won't add more.
Category: Environment & Habits
Biggest REM Killer
Alcohol
Key Stat: −11.3 min REM, +18 min delay
Even a couple of drinks delay REM, and each extra drink cuts more. A nightcap leaves you under-recovered.
Category: Substances & Nutrition
Most Defended
REM Rebound
Key Stat: 140% of baseline on recovery night
Lose REM and your brain pays it back the next night, with extra dream sleep on the first recovery night.
Category: Environment & Habits
Best Supplement
Melatonin (if your REM is low)
Key Stat: REM% 14.7% → 17.8% (low-REM patients)
Raised REM% in patients whose REM started abnormally low, but not in healthy men. For most people it's a timing aid, not a REM booster.
Category: Supplements
Most Overblown Worry
Caffeine
Key Stat: REM unchanged; deep sleep −11.4 min
A meta-analysis found no change in REM%, REM minutes or REM latency. Caffeine's real cost is deep sleep, not REM.
Category: Substances & Nutrition
What to change
Do more / cut back.
The changes with real evidence behind them, with the dose that was tested and what it did. Tap any row for the full study details.
Do more
4 habits that protect REM
- Sleep longer Protect the last hours of the night Short nights cut REM first Strong evidence
- Keep the bedroom cool Around 22°C; cool the bed in a heatwave 32°C room lowered REM Strong evidence
- Sleep on your body clock Regular hours; limit jet lag and shift swings REM peaks just after the body-temperature low Strong evidence
- Don't cut carbs to zero Higher-carb meals vs low-carb REM time and share up (11 trials) Moderate evidence
Cut back
8 things that cut or delay REM
- Alcohol From about 2 drinks; more, bigger hit REM 18 min later, 11.3 min shorter Strong evidence
- Hard late workouts Ending 0.5–4 h before bed REM −2 points; moderate is fine Strong evidence
- Nicotine Patch or smoking; more, bigger hit REM down by dose Moderate evidence
- All-night noise Steady noise machine or hum REM −18.6 min at 50 dB Moderate evidence
- Hours of bright screens 4 h before bed; 90 min was fine REM 109 vs 121 min Moderate evidence
- Stress before bed Wind down before lights out REM% down, more broken Moderate evidence
- Sleeping at altitude The higher, the bigger the cut REM share falls step by step Moderate evidence
- First night somewhere new Hotels, new bedrooms; gone by night 2 Less, later REM on night 1 Strong evidence
Show all 8
Only factors you can change, with strong or moderate evidence. Supplements that helped only in patients are left out; they stay in the full list below.
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Explore all 37 factors.
Pick a category, then tap any factor for its plain-English takeaway, mechanism, dose, and source.
Environment & Habits
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Substances & Nutrition
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Exercise
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Demographics & Body
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Most of the levers you control live here. REM is back-loaded into the last hours of the night and is sensitive to heat, noise and timing, so protecting the end of your night matters most.
Lowers REM
Alcohol is the clearest REM suppressor on this page, and nicotine is close behind. Caffeine, the usual suspect, does not cut REM at all: its cost lands on deep sleep.
Lowers REM
Lowers REM
The supplement literature for REM is thin. Only melatonin (in people whose REM is abnormally low) and ketone esters (after very hard training) moved REM in sleep-lab studies. Treat any "boosts REM" claim as unproven unless it cites REM on a sleep study (PSG).
Raises REM
REM is surprisingly stable across age, sex and genes. The clear sex and age differences are in deep sleep, not REM.
No clear effect
Age
~0.6 pts/decade, or none with modern scoring
Evidence: Strong
What this means
REM changes little with age. Total sleep and sleep efficiency carry most of the age decline.
Mechanism
Ageing mostly erodes deep sleep and sleep efficiency. REM, driven by brainstem circuits and the circadian clock, is comparatively well preserved.
Dose / context
REM% fell about 0.6 points per decade through most of adulthood, levelling off in the mid-70s; a 2019 meta with modern scoring found no significant change (0.0 points per decade). Floyd 2007 (382 studies, n=4,171); Boulos 2019 (169 studies, n=5,273).
Source
No clear effect
Sex / Hormones
REM% didn't vary with sex across 169 PSG studies
Evidence: Strong
What this means
REM is about the same in men and women. Deep sleep is where the sexes differ.
Mechanism
Sex differences show up in deep sleep, which is higher in women. Hormonal shifts within a person (menstrual phase, pregnancy) move REM more than sex itself.
Dose / context
REM% did not vary with the share of men across 169 PSG studies; the clear sex gap is deep sleep, which is higher in women. Boulos 2019 (n=5,273); Redline 2004 (SHHS, n=2,685).
Source
Boulos et al., Lancet Respir Med 2019
Lowers REM
Menstrual Cycle (Luteal)
Minor REM dip in the mid-luteal phase
Evidence: Moderate
What this means
REM dips a little in the two weeks before a period, likely because body temperature runs higher.
Mechanism
Progesterone raises core body temperature in the luteal phase, and REM is temperature-sensitive. The dip appears at specific circadian phases.
Dose / context
REM was reduced in the mid-luteal phase at specific circadian phases; reviews call it a minor luteal decrease, linked to higher body temperature. Shechter 2010 (n=8); Baker 1999.
Source
Lowers REM
Late Pregnancy
Fewer REM minutes in third trimester (lab PSG)
Evidence: Moderate
What this means
REM tends to be lower late in pregnancy, along with lighter sleep.
Mechanism
Late pregnancy brings physical discomfort, more awakenings, breathing changes and high progesterone, which together lighten sleep and trim REM.
Dose / context
27 women in the third trimester had fewer REM minutes than 24 non-pregnant women on lab PSG; small longitudinal studies are mixed.
Source
Wilson et al., Aust N Z J Obstet Gynaecol 2011
Lowers REM
Obesity (BMI 30+)
7.8 min less REM with apnea excluded (n=1,014)
Evidence: Moderate
What this means
Extra weight is linked to at most a few minutes less REM once sleep apnea is ruled out.
Mechanism
Much of the link between weight and poor sleep runs through sleep apnea, which fragments REM. With moderate or severe apnea excluded, the remaining REM gap is small.
Dose / context
With moderate or severe sleep apnea excluded, BMI 30+ had 7.8 min less REM (p=0.003); in 2,745 older men, REM was not linked to body composition. Pessoa 2025 (Baependi, n=1,014); Rao 2009 (MrOS).
Source
Lowers REM
Acute Illness
Evening endotoxin cut REM share (n=15)
Evidence: Emerging
What this means
Fighting an infection can trim REM for a night, but real colds haven't shown a clear REM drop.
Mechanism
Endotoxin raised body temperature and released immune signalling molecules (cytokines) and stress hormones; non-REM sleep rose and REM fell in step with them.
Dose / context
Endotoxin given in the evening cut REM share in healthy men (P<0.05); the same dose mid-sleep did not; a real cold cut sleep about 23 min with no REM change reported. Pollmächer 1993 (n=15); Haack 2001 (n=10); Drake 2000 (n=21).
Source
Pollmächer et al., Am J Physiol 1993
No clear effect
Genetics
REM heritability h2 0.07 (n.s.) vs deep sleep 0.35
Evidence: Emerging
What this means
How much REM you get looks driven more by circumstances than genes.
Mechanism
In family data, deep sleep was clearly heritable while REM time was not, suggesting REM depends more on circumstances than genes. Some twin studies disagree.
Dose / context
REM time showed no significant heritability (h2 0.07, p=0.19) while deep sleep did (0.35); some twin studies disagree. n=684 family members.
Source
Leocadio-Miguel et al., J Sleep Res 2025
Keep exploring
Melatonin
REM% ~14.7% → 17.8% in low-REM patients
Evidence: Moderate
What this means
Helps REM only if yours is abnormally low. Otherwise it's a timing aid.
Mechanism
Melatonin acts on the circadian clock, and REM follows the clock. In animals the MT1 receptor selectively enhances REM; in humans the REM gain showed up only in patients who started with reduced REM.
Dose / context
3 mg for 4 weeks raised REM% from about 14.7% to 17.8% (placebo fell to 12.0%) in sleep-disorder patients with low REM; in healthy men REM% did not change. Kunz 2004 (2 RCTs, n=14 total); Rajaratnam 2004 (n=8).
Source
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No clear effect
Valerian
REM unchanged after 28 days (n=184)
Evidence: Moderate
What this means
Valerian doesn't shift REM either way.
Mechanism
Valerian is thought to act on GABA and adenosine signalling. In sleep-lab studies that has not shown up as any change in REM.
Dose / context
REM unchanged after 28 days of valerian-hops in mild insomnia, and in two small PSG studies. Morin 2005 (n=184, industry funded); Schulz 1994; Balderer 1985.
Source
Protects REM
Ketone Ester After Hard Exercise
Kept REM at 117 vs 93 min after hard training
Evidence: Emerging
What this means
In trained cyclists, ketone drinks offset the REM loss from a very hard late training day. Untested in everyday life.
Mechanism
Hard training ending an hour before bed cut REM by 26% and nearly doubled time awake overnight. The ketone drink raised dopamine excretion, which the authors offer as a preliminary explanation; the pathway is not confirmed.
Dose / context
A hard training day ending 1 h before bed cut REM from 125 to 93 min; 25 g ketone ester after each session and 30 min before bed (75 g total) kept REM at 117 min (p=0.011 vs placebo). Robberechts 2023 (n=10, crossover); Poffé 2026 (n=24, 7 weeks).
Source
Robberechts et al., Med Sci Sports Exerc 2023
No clear effect
Glycine (3 g)
Faster sleep onset; REM unchanged (n=11)
Evidence: Emerging
What this means
Glycine may help you fall asleep faster but doesn't change REM.
Mechanism
Glycine lowers core body temperature and speeds entry into deep sleep, without changing REM latency or stage proportions.
Dose / context
Shortened time to fall asleep and to reach deep sleep; REM latency and stage proportions unchanged. n=11 poor sleepers, crossover; authors from Ajinomoto, a glycine maker.
Source
Yamadera et al., Sleep Biol Rhythms 2007
No clear effect
CBD (300 mg)
REM 17.6% placebo vs 16.6% CBD
Evidence: Emerging
What this means
One dose of CBD didn't change REM.
Mechanism
Unlike THC, CBD does not strongly activate CB1 receptors. A single 300 mg dose in healthy sleepers left sleep architecture, including REM, intact.
Dose / context
REM 17.6% placebo vs 16.6% CBD; REM latency also unchanged. n=26, crossover; authors hold CBD patents.
Source
Linares et al., Front Pharmacol 2018
Keep exploring
Evening Intense Exercise
Hard late session: REM −1.95 points (28 trials)
Evidence: Strong
What this means
Hard late workouts trim REM a little and push it later. Morning or moderate sessions don't.
Mechanism
A hard session close to bed likely keeps core temperature, heart rate and sympathetic drive raised into the first part of the night, which delays and trims REM. The studies measured single nights after one session.
Dose / context
One hard session (77%+ HRmax, ending 0.5 to 4 h before bed) cut REM by 1.95 points of total sleep vs no exercise; 2.5 points when it ran over 30 to 60 min. Moderate and light sessions: no significant change. Evening exercise also delayed REM onset by 7.7 min. Morning exercise showed no REM change in timing studies. Yue 2022 (network meta, 28 trials, n=325); Frimpong 2021 (−2.34 points); Stutz 2019 (23 studies).
Source
Yue et al., Nat Sci Sleep 2022
No clear effect
Cold Water Immersion After Exercise
No change in REM vs exercise alone (n=11)
Evidence: Emerging
What this means
An ice bath after an evening workout didn't change REM.
Mechanism
Cold water lowers core temperature after exercise, but REM timing and amount did not respond in this study.
Dose / context
No difference in stage proportions or REM onset vs exercise alone. n=11.
Source
Robey et al., Med Sci Sports Exerc 2013
Keep exploring
Alcohol
REM 18 min later, 11.3 min shorter (27-study meta)
Evidence: Strong
What this means
Even a couple of drinks delay REM, and each extra drink cuts more. This is why a nightcap leaves you under-recovered, and why using a drink to fall asleep backfires.
Mechanism
Alcohol's sedative (GABAergic) effect suppresses the cholinergic activity that generates REM early in the night. As it wears off, the rebound arousal and fragmentation hit the second half of the night, where REM concentrates.
Dose / context
REM started 18.0 min later and ran 11.3 min shorter (REM share −2.8 points). Each 1 g/kg added 30.1 min to REM onset and cut 40.4 min of REM. REM delay began around 0.35 g/kg (about 2 drinks), REM loss around 0.5 g/kg (about 3). Meta-analysis of 27 studies in healthy adults.
Source
Gardiner et al., Sleep Med Rev 2024
No clear effect
Caffeine
No change in REM% (k=19); deep sleep −11.4 min
Evidence: Strong
What this means
Caffeine doesn't cut REM. It cuts deep sleep.
Mechanism
Caffeine blocks adenosine receptors. Adenosine mainly drives deep-sleep pressure, so caffeine's clearest cost lands on slow-wave sleep, not REM.
Dose / context
No significant change in REM% (k=19), REM minutes (k=17) or REM latency (k=14); deep sleep fell 11.4 min. Meta-analysis.
Source
Gardiner et al., Sleep Med Rev 2023
Lowers REM
Nicotine
7 or 14 mg patch cut REM, dose-dependently
Evidence: Moderate
What this means
Nicotine cuts REM, and more nicotine cuts more. That held for a patch in non-smokers and for a 24-hour patch in smokers.
Mechanism
Nicotine activates acetylcholine receptors that promote arousal and fragment sleep. A patch keeps nicotine in the blood all night, so the effect covers the REM-heavy early morning.
Dose / context
A 7 or 14 mg patch cut REM time and REM% dose-dependently in non-smokers (n=12); a 24 h patch lowered REM% in smokers (n=15).
Source
Mixed
Cannabis / THC
High-dose THC suppresses REM; quitting rebounds it
Evidence: Moderate
What this means
Heavy THC can suppress dream sleep, and quitting brings vivid dreams back. At typical doses, the effect on REM is unclear.
Mechanism
THC acts on CB1 receptors and reduced REM eye movements and, less so, REM time in early high-dose studies. Stopping after regular use unmasks a consistent REM rebound.
Dose / context
High-dose THC reduced REM eye movements and, less so, REM time in small early studies; newer lower-dose studies show mixed or no change; REM rebound on withdrawal is consistent. Velzeboer 2025 (meta, 18 PSG studies); Feinberg 1975 (n=7).
Source
Velzeboer et al., Sleep Med Rev 2025
Raises REM
Diet (Carbs)
High-carb raised REM vs low-carb (11 trials)
Evidence: Moderate
What this means
More carbs nudges REM up a little. Low carb shifts sleep toward deep sleep instead.
Mechanism
Carbohydrate raises insulin, which helps tryptophan reach the brain for serotonin and melatonin synthesis, one proposed route to more REM. Low-carb diets shift the balance toward slow-wave sleep.
Dose / context
High-carb meals or diets raised REM time and share vs low-carb; low-carb raised deep sleep; REM latency unchanged. Meta-analysis of 11 short-term trials (n=179).
Source
Vlahoyiannis et al., Nutrients 2021
No clear effect
Late Dinner
REM 20.8% vs 20.6% (P=.87), crossover
Evidence: Moderate
What this means
Eating dinner an hour before bed didn't reduce REM.
Mechanism
A late dinner raised overnight glucose and cortisol and lowered fat burning in this study, but sleep architecture, including REM, held steady.
Dose / context
REM 20.8% vs 20.6% (P=.87) with dinner at 22:00 vs 18:00 (the 18:00 arm had a 22:00 snack). Crossover, n=20.
Source
Gu et al., J Clin Endocrinol Metab 2020
Lowers REM
Ramadan-Style Daytime Fasting
REM 25.6% → 18.6% during Ramadan (n=8)
Evidence: Emerging
What this means
Daytime fasting with a pre-dawn meal is linked to less REM, but the 3:30 am wake-up to eat may be the real cause. Both studies were small.
Mechanism
The pattern moves meals into the night and adds a pre-dawn wake-up, which breaks into the REM-rich early morning and shifts circadian cues. The studies cannot separate fasting itself from the schedule change.
Dose / context
REM share 25.6% at baseline vs 18.6% during Ramadan, with sleep times and calories fixed (p<0.05); a separate lab also found less REM. BaHammam 2013 (n=8); Roky 2001 (n=8).
Source
BaHammam et al., Behav Brain Funct 2013
Keep exploring
Short Sleep / Early Alarm
4 h vs 9 h: REM minutes cut first (n=27)
Evidence: Strong
What this means
REM is back-loaded, so a short night with a fixed alarm cuts it first.
Mechanism
REM is concentrated in the early morning, so cutting sleep short trims REM more than any other stage, while deep sleep's share actually rises.
Dose / context
4 h vs 9 h for 5 nights cut REM and stage 2 minutes, while deep sleep's share rose. n=27, crossover, PSG.
Source
Shechter et al., Am J Physiol 2012
Lowers REM
Bedroom Heat
32°C room lowered REM vs 22°C; cooling restored it
Evidence: Strong
What this means
A hot, especially humid, bedroom costs you REM. Staying cool protects it, but going colder won't add more.
Mechanism
During REM the body largely suspends temperature control (little effective sweating or shivering), so the sleeper is exposed to the room. Animal studies suggest the brain shortens REM in heat to protect body temperature.
Dose / context
A 32°C bedroom cut total sleep by 24.8 min and lowered REM vs 22°C; a cooling mattress topper restored 21.4 min of sleep and the lost REM. At normal room temperature, cooling added deep sleep, not REM. Pasquier 2025 (n=15, crossover, PSG); Kräuchi 2024 (n=72).
Source
Pasquier et al., J Sleep Res 2025
Lowers REM
Unfamiliar Room (First Night)
Less, later REM on night 1 (53-study meta)
Evidence: Strong
What this means
Your first night in a hotel or new bedroom costs some REM. It recovers by night two.
Mechanism
In a new place the brain likely stays partly on guard, so sleep is lighter and more broken, and REM starts later and runs shorter until the setting feels familiar.
Dose / context
Across 53 studies, the first night in a new sleep setting had less REM and a later REM onset than the second night (p ≤ 0.001); smallest at ages 20 to 29. Meta-analysis, n=1,422.
Source
Raises REM
REM Deprivation
REM rose to 140% of baseline on recovery night
Evidence: Strong
What this means
Lose REM and your brain pays it back the next night.
Mechanism
REM is homeostatically regulated: a REM debt builds pressure that is repaid with extra REM on recovery nights, scaled to the size of the debt.
Dose / context
3 nights of selective REM deprivation cut REM to 9.2% of baseline; it rose to 140.1% on the first recovery night. n=8 men.
Source
Endo et al., Am J Physiol 1998
Sets timing
Circadian Timing
REM peaks just after the body-temperature low
Evidence: Strong
What this means
Most REM lands in the last hours of the night. Jet lag and shift work misalign it.
Mechanism
REM is gated by the circadian clock. Its propensity peaks just after the core body temperature minimum, on the rising part of the curve, which normally falls in the early morning.
Dose / context
REM propensity peaks just after the body temperature low point, on the rising part of the curve. n=10, 306 subject-days.
Source
Lowers REM
Continuous Background Noise
50 dB pink noise cut REM 18.6 min (n=25)
Evidence: Moderate
What this means
A constant noise machine or hum can trim REM. Earplugs mostly protect deep sleep, not REM.
Mechanism
Why steady broadband sound cuts REM is not established. The effect is specific: steady pink noise reduced REM, while on-and-off noise peaks mainly cut deep sleep, which earplugs protected.
Dose / context
50 dB pink noise all night cut REM by 18.6 min (118.1 to 99.5 min); 32 dB wind turbine noise cut REM 11.1 min and delayed it 16.8 min. On-and-off traffic noise mainly cut deep sleep instead. Basner 2026 (n=25, randomized crossover); Smith 2020 (n=48); same research group.
Source
Lowers REM
Evening Screens
4 h iPad: REM 109 vs 121 min; 90 min phone: no change
Evidence: Moderate
What this means
Hours of bright screen time before bed can trim REM. A normal evening on your phone did not.
Mechanism
Hours of bright, blue-rich light in the evening suppress and delay melatonin, pushing the body clock later. REM follows the clock, so a fixed alarm cuts into it.
Dose / context
4 h of iPad reading at full brightness for 5 evenings: REM 109 vs 121 min with a printed book (p=0.03). 90 min of phone reading ending 50 min before bed: REM unchanged (about 19 to 20%). Chang 2015 (n=12, crossover); Höhn 2024 (n=62).
Source
Lowers REM
Presleep Stress
Lab stressor lowered REM% and raised REM density
Evidence: Moderate
What this means
Stress before bed chops REM up. People whose sleep reacts to stress lose the most.
Mechanism
Stress raises cortisol and arousal into the night. In people with high sleep reactivity, that fragments REM, lowers REM time and loads it with more eye movements.
Dose / context
A lab stressor before bed lowered REM% and raised REM density; REM minutes fell only in people with stress-reactive sleep. n=62, PSG.
Source
Feng et al., Nat Sci Sleep 2023
Lowers REM
Altitude
Higher altitude, less REM (4,559 m vs 490 m)
Evidence: Moderate
What this means
Sleeping high cuts REM, and higher cuts more.
Mechanism
Low oxygen triggers periodic breathing and frequent arousals, which break up REM and deep sleep. The thinner the air, the bigger the effect.
Dose / context
At 4,559 m, REM and deep sleep share fell across nights 1 to 4 vs 490 m; simulated 2,000 and 4,000 m cut REM share step by step. Nussbaumer-Ochsner 2011 (n=14); Li 2021 (n=25).
Source
Nussbaumer-Ochsner et al., High Alt Med Biol 2011
No clear effect
Daytime Napping
Naps didn't reduce the next night's REM (n=38)
Evidence: Moderate
What this means
Naps don't eat into your nighttime REM. A late nap may shift when it starts.
Mechanism
Naps spend some sleep pressure, which mostly drives deep sleep. REM follows the circadian clock more than sleep pressure, so nighttime REM amount holds.
Dose / context
Naps from 09:00 to 18:00 did not reduce the next night's REM in young or older adults; an early-evening nap made REM start sooner. Campbell 2005 (n=38); Werth 1996.
Source
Campbell et al., Neurobiol Aging 2005
No clear effect
Phone Radio Signals
Sleep architecture unchanged (double-blind)
Evidence: Moderate
What this means
Phone signals haven't been shown to change REM.
Mechanism
Phone-type radio exposure has nudged some EEG power bands in lab studies, but not the amount or timing of sleep stages.
Dose / context
GSM-type exposure before or during sleep left sleep architecture unchanged (double-blind). Regel 2007 (n=15); Fritzer 2007 (n=10).
Source
Regel et al., J Sleep Res 2007
Lowers REM
Sleeping Sitting Up
Upright seat: 79% less REM than flat (n=6)
Evidence: Emerging
What this means
Sleeping upright on a plane or in a car cuts REM most. Recline as far as you can.
Mechanism
The authors give two likely reasons: the head is hard to keep comfortable upright, worse in REM when muscle tone is very low, and an upright posture raises sympathetic (fight-or-flight) activity, keeping the body more aroused.
Dose / context
In a 4 h daytime nap, an upright seat gave 79% less REM than a flat seat; a 40° recline gave 37% less. n=6, within-subject.
Source
Roach et al., Chronobiol Int 2018
Lowers REM
Hot Bath Right Before Bed
Bath at 21:00 cut REM; at 17:00 it didn't
Evidence: Emerging
What this means
Heating your body hard right before bed pushes REM back. An earlier bath didn't.
Mechanism
Heating the body close to bedtime raised deep sleep and lowered REM. Aspirin, which blunts the temperature response, mostly cancelled the effect, pointing to the late rise in body heat as the driver.
Dose / context
A bath at 21:00 raising core temperature about 2°C cut REM; the same bath at 17:00 changed nothing. 1 h at 41°C ending just before sleep shortened the first REM period. Horne & Shackell 1987 (n=6); Bunnell 1988.
Source
Raises REM
Sleeping Next to a Partner
REM 23.0% with partner vs 21.0% alone (n=24)
Evidence: Emerging
What this means
Sharing a room with your partner was linked to slightly more, less broken REM.
Mechanism
Not established. Couples' sleep stages synchronised when they shared a bed, and people with less social support gained the most REM. The authors propose a feedback loop between REM sleep and social bonds.
Dose / context
REM share 23.0% beside a partner vs 21.0% alone, with fewer REM interruptions (8.5 to 5.4); no other stage changed. n=24 (12 couples), within-subject.
Source
Drews et al., Front Psychiatry 2020
Raises REM
Presleep Learning
Fastest learners had the biggest REM% rise (n=10)
Evidence: Emerging
What this means
REM tracks how much you learn. Small study.
Mechanism
REM supports consolidation of procedural and emotional memory. In an immersion course, the rise in REM% tracked how fast students learned the language.
Dose / context
Students who learned French fastest in a 6-week immersion course showed the biggest rises in REM%. n=10.
Source
De Koninck et al., Int J Psychophysiol 1989
No clear effect
Mattress Type
REM unchanged across 4 mattresses (P>0.05)
Evidence: Emerging
What this means
Mattress choice didn't move REM.
Mechanism
How evenly the mattress spread body pressure changed deep sleep and micro-arousals in this study, but not REM. The authors say the underlying mechanism is unknown.
Dose / context
REM unchanged across 4 mattresses (all P>0.05); deep sleep did change. n=16; run by the mattress maker.
Source
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Sources
Every claim, traceable.
Each factor is anchored to a primary peer-reviewed source. Last updated October 2026.
Substances & Nutrition
Alcohol
Gardiner et al., Sleep Med Rev 2024
Substances & Nutrition
Nicotine
Gillin et al., 1994
Substances & Nutrition
Ramadan-Style Daytime Fasting
BaHammam et al., Behav Brain Funct 2013
Substances & Nutrition
Cannabis / THC
Velzeboer et al., Sleep Med Rev 2025
Substances & Nutrition
Diet (Carbs)
Vlahoyiannis et al., Nutrients 2021
Substances & Nutrition
Caffeine
Gardiner et al., Sleep Med Rev 2023
Substances & Nutrition
Late Dinner
Gu et al., J Clin Endocrinol Metab 2020
Supplements
Melatonin
Kunz et al., JCEM 2004
Supplements
Ketone Ester After Hard Exercise
Robberechts et al., Med Sci Sports Exerc 2023
Supplements
Glycine (3 g)
Yamadera et al., Sleep Biol Rhythms 2007
Supplements
Valerian
Morin et al., Sleep 2005
Supplements
CBD (300 mg)
Linares et al., Front Pharmacol 2018
Exercise
Evening Intense Exercise
Yue et al., Nat Sci Sleep 2022
Exercise
Cold Water Immersion After Exercise
Robey et al., Med Sci Sports Exerc 2013
Environment & Habits
Short Sleep / Early Alarm
Shechter et al., Am J Physiol 2012
Environment & Habits
Bedroom Heat
Pasquier et al., J Sleep Res 2025
Environment & Habits
Unfamiliar Room (First Night)
Ding et al., Sleep Med 2021
Environment & Habits
Continuous Background Noise
Basner et al., Sleep 2026
Environment & Habits
Evening Screens
Chang et al., PNAS 2015
Environment & Habits
Presleep Stress
Feng et al., Nat Sci Sleep 2023
Environment & Habits
Altitude
Nussbaumer-Ochsner et al., High Alt Med Biol 2011
Environment & Habits
Sleeping Sitting Up
Roach et al., Chronobiol Int 2018
Environment & Habits
Hot Bath Right Before Bed
Horne & Shackell, Sleep 1987
Environment & Habits
Sleeping Next to a Partner
Drews et al., Front Psychiatry 2020
Environment & Habits
Presleep Learning
De Koninck et al., Int J Psychophysiol 1989
Environment & Habits
REM Deprivation
Endo et al., Am J Physiol 1998
Environment & Habits
Circadian Timing
Czeisler et al., Science 1980
Environment & Habits
Daytime Napping
Campbell et al., Neurobiol Aging 2005
Environment & Habits
Mattress Type
Chen et al., PLoS One 2014
Environment & Habits
Phone Radio Signals
Regel et al., J Sleep Res 2007
Demographics & Body
Age
Floyd et al., Sleep 2007
Demographics & Body
Sex / Hormones
Boulos et al., Lancet Respir Med 2019
Demographics & Body
Menstrual Cycle (Luteal)
Shechter et al., Sleep 2010
Demographics & Body
Late Pregnancy
Wilson et al., Aust N Z J Obstet Gynaecol 2011
Demographics & Body
Obesity (BMI 30+)
Pessoa et al., Obesity 2025
Demographics & Body
Acute Illness
Pollmächer et al., Am J Physiol 1993
Demographics & Body
Genetics
Leocadio-Miguel et al., J Sleep Res 2025
Show all 37 sources
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