Summary
Deep sleep (slow wave sleep) is when the body and brain recover most. It falls naturally with age, but daily habits can nudge it back up.
Regular exercise, a warm shower or bath before bed, a cool bedroom, less alcohol and a steady schedule have the best evidence. Nutrients such as glycine and magnesium may help as a supporting act.
You slept eight hours, so why do you wake up feeling flat? Often the answer is not how long you slept but how deeply. If your sleep tracker shows little deep sleep, or you simply never feel restored, this guide explains what deep sleep is, why it shrinks, and seven habits that research suggests can help.
What is deep sleep?
Each night you cycle through light sleep, deep sleep and REM (dreaming) sleep. Deep sleep, also called slow wave sleep or N3, is when brain waves become slow and large. It is concentrated in the first half of the night and is linked to physical recovery, memory consolidation and immune function.
It also matters for metabolism. A 2022 meta analysis in Sleep Medicine Reviews found that suppressing slow wave sleep in experiments reduced insulin sensitivity, a sign that the body handles blood sugar less efficiently.
Why deep sleep declines
A large meta analysis in the journal Sleep (2004), covering 65 studies and 3,577 healthy people, showed that the share of slow wave sleep drops steadily through adulthood. Stress, alcohol, a warm room, irregular hours and untreated sleep apnoea can push it down further.
7 habits for more deep sleep
1. Move most days
A 2025 network meta analysis in Sleep Medicine pooled 18 randomised trials with 1,214 adults with sleep problems. Exercise increased slow wave sleep, and training four or more times a week worked best for deep sleep. Moderate aerobic exercise, such as brisk walking, cycling or swimming, gave the best overall results.
2. Do not fear evening workouts, just finish early
A 2019 meta analysis in Sports Medicine (23 studies) found that evening exercise slightly increased slow wave sleep rather than harming sleep. The exception was vigorous exercise ending within an hour of bedtime, which could delay sleep.
3. Take a warm shower or bath 1 to 2 hours before bed
Your core temperature needs to drop for deep sleep. Warm water draws blood to the skin, which then releases heat. A 2019 meta analysis found that water at 40 to 42.5 °C, 1 to 2 hours before bed, improved sleep quality and helped people fall asleep faster, even after just 10 minutes.
4. Keep the bedroom cool and dark
For the same reason, a cool room helps. Most sleep experts suggest around 16 to 19 °C, breathable bedding and blackout curtains.
5. Do not use alcohol as a sleep aid
Alcohol is tricky. A review in Alcoholism: Clinical and Experimental Research (2013) found that it can increase deep sleep early in the night, but it disrupts the second half of the night and suppresses REM sleep. The net result is lighter, more broken sleep.
6. Keep a steady schedule
Your body clock times deep sleep. Going to bed and waking at the same times, even at weekends, keeps that timing stable. See the power of a sleep routine.
7. Support the evening with nutrients
Two nutrients have interesting early data. Glycine, an amino acid, appears to lower core body temperature by increasing blood flow to the skin, and it improved self rated sleep quality in people with poor sleep (Journal of Pharmacological Sciences, 2012). Magnesium L threonate improved deep sleep scores measured by a wearable ring in a 2024 trial. Read our full guide to magnesium for sleep.
Deep sleep is driven by pressure and temperature: a day of movement builds the pressure, and a cooling body in the evening opens the door.
The habits at a glance
| Habit | What the research found | Practical tip |
|---|---|---|
| Regular exercise | More slow wave sleep, best at 4 or more sessions a week (18 trials) | 30 to 60 minutes of moderate cardio most days |
| Evening exercise | Slightly more slow wave sleep (23 studies) | Finish hard sessions at least an hour before bed |
| Warm shower or bath | Faster sleep onset and better sleep quality | 40 to 42.5 °C, 1 to 2 hours before bed |
| Cool bedroom | Supports the natural fall in core temperature | Around 16 to 19 °C |
| Less alcohol | Disrupts the second half of the night | Stop drinking a few hours before bed |
| Glycine and magnesium | Early data on sleep quality and deep sleep scores | Take with your evening routine |
When to see a doctor
Loud snoring, gasping at night, morning headaches or heavy daytime sleepiness can be signs of sleep apnoea, which fragments deep sleep and needs proper assessment. No habit or supplement replaces that.
Where Morphéon fits
Morphéon combines L Glycine and magnesium glycinate with L Tryptophan, lemon balm, chamomile, lavender, zinc and chromium, in liposomal capsules and with no melatonin. Magnesium contributes to normal psychological function and to the reduction of tiredness and fatigue. Use it alongside the habits above, not instead of them. Living in Ireland? Read can you buy melatonin in Ireland.
Frequently asked questions
How much deep sleep do I need?
There is no single target. In healthy adults deep sleep typically makes up a smaller share of the night with every decade. How rested you feel during the day is a better guide than a tracker number.
Why am I not getting deep sleep?
Common reasons include age, stress, alcohol, a warm bedroom, an irregular schedule and sleep apnoea. Exercise and evening cooling are the most reliable ways to increase it.
Are sleep trackers accurate for deep sleep?
Wearables estimate sleep stages from movement and heart rate, so they are useful for trends but less precise than a sleep laboratory. Look at changes over weeks, not single nights.
Does magnesium increase deep sleep?
A 2024 trial with magnesium L threonate found better deep sleep scores on a wearable ring. Evidence is still early, so magnesium is best seen as a support for good habits.
Does alcohol help deep sleep?
It can increase deep sleep early in the night, but it disrupts the second half of the night and reduces REM sleep, so overall sleep quality suffers.
Bottom line
To get more deep sleep, build sleep pressure with regular movement, help your body cool down in the evening, keep alcohol away from bedtime and protect a steady schedule. Glycine and magnesium can support that routine.
Explore Morphéon →Related reading: why sleep is the foundation of health · HYPNOS
Sources
- Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals. Sleep. 2004. doi.org/10.1093/sleep/27.7.1255
- Sondrup N, Termannsen AD, Eriksen JN, et al. Effects of sleep manipulation on markers of insulin sensitivity: A systematic review and meta-analysis of randomized controlled trials. Sleep Medicine Reviews. 2022. doi.org/10.1016/j.smrv.2022.101594
- Wang P, Chen Y, Zhang A, Xie C, Wang K. Comparative efficacy of exercise modalities on sleep architecture in adults with sleep disorders: a systematic review and network meta-analysis of randomized controlled trials. Sleep Medicine. 2025. doi.org/10.1016/j.sleep.2025.106680
- Stutz J, Eiholzer R, Spengler CM. Effects of Evening Exercise on Sleep in Healthy Participants: A Systematic Review and Meta-Analysis. Sports Medicine. 2019. doi.org/10.1007/s40279-018-1015-0
- Haghayegh S, Khoshnevis S, Smolensky MH, Diller KR, Castriotta RJ. Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews. 2019. doi.org/10.1016/j.smrv.2019.04.008
- Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research. 2013. doi.org/10.1111/acer.12006
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of Pharmacological Sciences. 2012. doi.org/10.1254/jphs.11r04fm
- Hausenblas HA, Lynch T, Hooper S, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: A randomized controlled trial. Sleep Medicine: X. 2024. doi.org/10.1016/j.sleepx.2024.100121
