How to Get More Deep Sleep (And Why It Matters) | DELIM

March 7, 2026 Amirhossein Delkhosh

You're not just unconscious for eight hours. Every night your brain cycles through a sequence of sleep stages — and one of them is doing the heavy lifting while you lie there completely oblivious to it. Deep sleep, also called slow-wave sleep, is where your body actually recovers. Without enough of it, you can clock a full night and still wake up feeling like you've been hit by a bus.

Most people know they should sleep more. Far fewer understand that it's the quality of sleep — specifically how much time you spend in deep sleep — that determines how restored you actually feel. This guide breaks down what deep sleep is, why you're probably not getting enough, and exactly what to do about it.

What Is Deep Sleep?

Deep sleep is stage three of non-REM sleep, and it's the most physically restorative stage of the entire sleep cycle. Your brain waves slow to what scientists call delta waves — long, rolling electrical pulses that look nothing like the frantic activity you produce while you're awake. Your heart rate drops, your muscles relax fully, and your body gets to work.

This is when your pituitary gland releases the bulk of your nightly human growth hormone (HGH) — the hormone responsible for muscle repair, tissue regeneration, and cellular recovery. It's also when your brain consolidates memories, flushing out metabolic waste products (including beta-amyloid, linked to Alzheimer's disease) through the glymphatic system. Deep sleep isn't optional if you want to perform, think clearly, or stay healthy long-term.

A healthy adult should spend roughly 13–23% of total sleep time in deep sleep — that's around 90 to 120 minutes per night for someone getting eight hours. Most people fall well short of that. Here's why.

Why Most People Don't Get Enough Deep Sleep

Several forces work against deep sleep on a nightly basis, and the average modern lifestyle stacks almost all of them.

Age is the biggest factor. Deep sleep naturally declines as you get older — people in their 60s and 70s can get as little as 20 minutes of slow-wave sleep per night compared to around 90 minutes in young adults. That's not inevitable doom, but it does mean you need to protect the deep sleep you can still access.

Alcohol is widely misunderstood. Yes, it makes you fall asleep faster. No, it does not improve sleep quality — it actively suppresses slow-wave sleep and fragments the second half of the night. That groggy morning feeling after drinking isn't a hangover symptom. It's deep sleep debt.

Chronic stress and elevated cortisol keep your nervous system in a low-level alert state that makes it harder for your brain to reach and sustain slow-wave sleep. Stress doesn't just ruin your mood — it structurally interrupts your sleep architecture.

And then there's mouth breathing — the one nobody talks about. Breathing through your mouth during sleep creates a cascade of physiological disruptions that repeatedly drag you out of deep sleep before you've had a chance to benefit from it. We cover the full picture in our guide to mouth breathing during sleep, but the short version is: if your mouth is open at night, your deep sleep is almost certainly suffering.

How Mouth Breathing Steals Your Deep Sleep

Here's the mechanism, and it's worth understanding properly. When you breathe through your mouth during sleep, several things go wrong simultaneously.

First, mouth breathing dries out the airway and increases airflow resistance. This triggers micro-arousals — brief moments where your brain shifts from deep sleep back into lighter sleep stages to regulate breathing. You don't necessarily wake up fully. You just get yanked out of slow-wave sleep over and over without knowing it.

Second, mouth breathing bypasses your nose — the organ specifically designed to filter, humidify, and regulate the air going into your lungs. Nasal breathing produces nitric oxide, a molecule that dilates blood vessels and helps maintain stable blood oxygen saturation. Mouth breathing skips this process entirely. Lower, more variable blood oxygen during sleep = more stress signals to the brain = more micro-arousals = less deep sleep.

Third, mouth breathing is associated with a higher incidence of sleep-disordered breathing, including snoring and obstructive events. Every time your airway partially or fully collapses, your brain has to fire an arousal response to restart proper breathing. These events are devastating to sleep architecture. (If you suspect you have sleep apnoea, speak to your GP — mouth tape alone isn't a treatment for that.)

The result: you might spend eight hours in bed, but a significant portion of what should be restorative deep sleep gets replaced by fragmented, shallow sleep. You feel the difference every morning.

Try DELIM Mouth Tape tonight and give your body a fighting chance at the deep sleep it's actually supposed to be getting.

How to Get More Deep Sleep: Evidence-Backed Strategies

Fixing your deep sleep isn't complicated, but it does require consistency. These strategies work — use all of them, not just the ones that feel convenient.

1. Lock in a consistent sleep schedule. Your circadian rhythm controls when your body is primed to enter deep sleep. Going to bed and waking at the same time every day — including weekends — reinforces this rhythm powerfully. A single late night can push your slow-wave sleep window hours out of alignment.

2. Cut alcohol, especially after dinner. Alcohol is a deep sleep suppressor. If you drink in the evening, you're actively trading slow-wave sleep for sedation. They are not the same thing. Even two units in the evening measurably reduces deep sleep time according to multiple controlled studies.

3. Keep your bedroom cool. Core body temperature needs to drop to initiate and sustain deep sleep. A room temperature between 16–19°C (60–67°F) supports this process. A warm room works against it. This is one of the simplest, most evidence-backed environmental changes you can make.

4. Time your exercise well. Vigorous exercise increases slow-wave sleep — it's one of the most reliable ways to boost deep sleep quality. However, intense training within two to three hours of bedtime can delay sleep onset and reduce deep sleep in some people. Morning or early afternoon sessions tend to produce the best sleep outcomes.

5. Limit caffeine after midday. Caffeine has a half-life of five to seven hours. An afternoon coffee is still meaningfully active in your bloodstream at midnight. It suppresses adenosine — the sleep-pressure chemical — and makes it harder to reach and sustain deep sleep stages.

6. Reduce blue light exposure in the evening. Artificial light, especially from screens, suppresses melatonin and delays the onset of deep sleep. Use blue light filters or switch to warmer lighting in the two hours before bed.

7. Breathe through your nose. This is the one most people skip because it sounds too simple. It's not simple — for chronic mouth breathers, switching to nasal breathing at night is a significant physiological shift. But it's also one of the highest-leverage changes you can make for deep sleep quality.

For more detailed, actionable guidance on building the environment and habits that support quality sleep, see our full breakdown of sleep hygiene tips.

How Nasal Breathing Maximises Deep Sleep

Nasal breathing isn't just marginally better than mouth breathing. It's the biological default — the method your respiratory system was designed for — and it has specific, measurable effects on sleep quality.

The nose produces nitric oxide, which isn't produced by the mouth. Nitric oxide plays a direct role in regulating blood pressure, dilating blood vessels, and maintaining stable oxygen levels in the blood. During sleep, stable blood oxygen means fewer stress signals to the brain, fewer micro-arousals, and more time spent in the deep stages where recovery actually happens.

Nasal breathing also activates the parasympathetic nervous system more effectively than mouth breathing. Your parasympathetic system is the rest-and-digest mode — the biological opposite of the fight-or-flight response. Sustained parasympathetic activation during sleep is associated with deeper, more consolidated slow-wave sleep and better REM sleep.

There's also the structural argument. Nasal breathing maintains better muscle tone in the upper airway, reducing the likelihood of snoring and partial airway collapse — both of which fragment sleep architecture and cut into deep sleep time.

The simplest, most effective way to enforce nasal breathing during sleep is mouth tape. DELIM Mouth Tape is specifically designed for this — a skin-safe, breathable tape that keeps your mouth gently closed through the night, redirecting airflow through the nose without causing discomfort. No gadgets. No learning curve. Just better breathing from the moment you fall asleep.

Grab yours here and start protecting your deep sleep tonight.

Conclusion

Deep sleep is the most restorative stage of the night, and most people are getting far less of it than they should. Age, alcohol, stress, and — critically — mouth breathing all work to fragment and suppress slow-wave sleep. The good news: most of these factors are within your control.

Fix your schedule. Cool your room. Cut evening alcohol. Time your exercise. And address your breathing. If you're a mouth breather, that last point isn't optional — it's the foundation everything else sits on. Nasal breathing stabilises your blood oxygen, reduces micro-arousals, and gives your brain the sustained deep sleep window it needs to do its job.

For a broader plan to improve your overall sleep quality — not just deep sleep — start with our hub guide: How to Improve Sleep Quality. It covers every pillar that determines how well you sleep and how recovered you feel.

Try DELIM Mouth Tape tonight. Your deep sleep will thank you.

Resources

Carrier, J. et al. (2011). Sleep slow wave changes during the middle years of life. European Journal of Neuroscience, 33(4), 758–766. — Evidence on age-related decline in slow-wave sleep.
Ebrahim, I.O. et al. (2013). Alcohol and sleep I: Effects on normal sleep. Alcoholism: Clinical and Experimental Research, 37(4), 539–549. — Documents alcohol's suppressive effect on slow-wave sleep.
Meerlo, P. et al. (2008). Restricted and disrupted sleep: Effects on autonomic function, neuroendocrine stress systems and stress responsivity. Sleep Medicine Reviews, 12(3), 197–210. — Links stress/cortisol to impaired deep sleep architecture.
Lundberg, J.O. (2008). Nitric oxide and the paranasal sinuses. The Anatomical Record (Hoboken), 291(11), 1479–1484. — Key source on nasal nitric oxide production and its physiological role.
Horne, J.A. & Staff, L.H.E. (1983). Exercise and sleep: Body-heating effects. Sleep, 6(1), 36–46. — Establishes the relationship between exercise and slow-wave sleep promotion.
Ohayon, M.M. et al. (2004). Meta-analysis of quantitative sleep parameters from childhood to old age. Sleep, 27(7), 1255–1273. — Normative data on sleep stage distribution across the lifespan.