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How to Increase Deep Sleep: 7 Changes, Ranked by Evidence

Seven changes tied to more deep sleep in studies, how big the effects are where they were measured, and two popular fixes that work against you.

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NSDR.co
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11 min read
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The short version of how to increase deep sleep: keep the bedroom cool and quiet, stop caffeine about nine hours before bed, exercise, get bright light early in the day, put the phone away for the last hour and skip the nightcap. Each has been tied to more deep sleep, or less of it lost, in at least one study. Where it was measured, the effect was a few minutes a night, so stack them. Two popular fixes, a nightcap and a pink noise machine, work against you.

What deep sleep is, and how much you get

Deep sleep is stage 3 of non-REM sleep, also called slow-wave sleep. Adults spend about 10 to 20% of the night in it, roughly 40 to 110 minutes on seven to nine hours of sleep. Most of it comes in the first half of the night.

During deep sleep the body produces high levels of growth hormone and does tissue repair. The Sleep Foundation adds that it likely supports memory and immune function.

Deep sleep falls with age. Across 149 healthy men in four sleep labs, it dropped from 18.9% of the night in early adulthood to 3.4% at 36 to 50. In older adults, low deep sleep has been linked to later high blood pressure (784 men aged 65 or older), and losing deep sleep faster with age has been linked to dementia (346 people in the Framingham study). Those are associations, and they don't show that adding deep sleep prevents either. More on how the sleep stages fit together.

7 ways to increase deep sleep

Here is how to increase deep sleep, ordered by how directly the research measured it, strongest first.

Deep sleep prep runs all day: morning light, a 9-hour caffeine cutoff, then a cool, quiet bedroom.
Deep sleep prep runs all day: morning light, a 9-hour caffeine cutoff, then a cool, quiet bedroom.

1. Keep the bedroom cool

In normal bedding, a hot room increases waking and cuts both slow-wave and REM sleep, according to a review of the thermal research. The Sleep Foundation suggests 65 to 68 °F (about 18 to 20 °C). Huberman's sleep newsletter puts it at about 67 °F (19.4 °C) and says your core temperature has to fall by about 1 °C as you fall asleep.

A warm bath or shower 1 to 2 hours before bed helps the same cooling. In a 2019 meta-analysis, water at 40 to 42.5 °C (104 to 108.5 °F), for as little as 10 minutes, helped people fall asleep faster and rate their sleep better. The analysis didn't report a deep sleep gain, so treat the bath as a way to fall asleep faster.

2. Stop caffeine about nine hours before bed

A 2023 meta-analysis of 24 studies found caffeine cut deep sleep by about 11 minutes and total sleep by 45. Small doses count. In eight young men, 100 mg at bedtime, roughly one coffee, reduced the deepest stage of sleep.

To protect total sleep, the same meta-analysis puts the cutoff at 8.8 hours before bed for coffee and 13.2 hours for a standard pre-workout drink. For a 10:30 pm bedtime, that means the last coffee by about 1:40 pm. Caffeine's half-life averages about four hours but ranges from two to eight, so some people clear it far more slowly than others. More on how long caffeine stays in you.

3. Block noise with earplugs

Noise can cut deep sleep. In a 2026 sleep-lab study of 25 adults, bursts of environmental noise cut deep sleep compared with a quiet night, and earplugs undid nearly all of that until the noise reached its loudest level, 65 dB.

The same study tested pink noise as a mask. On its own at 50 dB, pink noise cut REM sleep by about 19 minutes, and adding it to the environmental noise made overall sleep structure worse. For outside noise, try earplugs first, and if you use a sound machine, treat 50 dB as a ceiling, not a target. More on what the pink noise studies found.

4. Exercise, including in the evening

Exercise helps a little. Across 66 studies, a single day's exercise gave a small boost to slow-wave sleep, and regular exercise had a moderate benefit for overall sleep quality.

The old rule to finish three hours before bed doesn't hold up. Across 23 studies, exercising in the evening slightly increased slow-wave sleep, by 1.3 percentage points. The one exception was hard exercise ending within about an hour of bedtime, which might delay sleep and cut sleep time.

5. Get bright light early in the day

Huberman's sleep toolkit says to go outside within 30 to 60 minutes of waking, for about 10 minutes on a clear day, 20 when it's cloudy and 30 to 60 when it's very overcast, without sunglasses if that's safe.

The deep sleep evidence is thin. In a field study of 20 adults wearing home sleep-recording kits, those who got bright light early built up more slow-wave sleep that night. It was observational, and the authors call for trials to confirm it.

6. Put the phone away for the last hour

In a Salzburg sleep-lab study of 33 young men, those who read on a smartphone for 90 minutes before bed got less deep sleep in the first quarter of the night than when they read a printed book. A blue-light filter softened some of the effects.

The often-quoted claim that 30 minutes on your phone in bed costs 20 minutes of deep sleep comes from a 75-person ring-tracker study where that effect wasn't statistically significant.

7. Eat more fibre, and leave about two hours after dinner

In a sleep-lab study of 26 adults, more fibre in the day's food predicted more slow-wave sleep, more saturated fat predicted less, and more sugar went with more brief arousals. It's one small study, so take it as a nudge toward more fibre.

Huberman's newsletter says a meal about two hours before bed doesn't affect sleep for most people. Eating closer to bedtime can make reflux more likely.

Why a nightcap is a bad trade

A 2013 review of every known study in healthy volunteers found that alcohol, at all doses, helps you fall asleep, and most studies found more deep sleep in the first half of the night. The cost comes later, with more broken sleep in the second half and less REM at moderate and high doses.

In a 1980 study of six young adults, even 0.16 g per kg of body weight (a bit under one US standard drink for a 70 kg person) reduced slow-wave sleep in the later part of the night. In 4,098 Finnish employees wearing heart monitors, a heart-rate measure of recovery in the first three hours of sleep fell by 9.3 percentage points after low intake (up to 0.25 g per kg) and by 39.2 after high intake. On nights when sleep matters, skip it.

What to do if you wake at 3am

If you've been lying awake for more than about 20 to 25 minutes, get up, go to another room and do something relaxing until you feel sleepy, then go back to bed. The aim is to stop your brain linking the bed with being awake.

While you wait, give your mind a job. In a study of 41 people with insomnia, those told to imagine an engaging scene in detail fell asleep faster than those given no instructions. Huberman suggests a "mental walk" along a route you know well.

Huberman's sleep toolkit also suggests "doing an NSDR protocol" if you wake in the night and can't fall back asleep. No study has tested that directly. The closest is a small trial in people with chronic insomnia, where 21 practised supervised yoga nidra, the practice NSDR draws on. In those who repeated a sleep-lab night, the share of the night in deep sleep went up. The comparison group had CBT for insomnia, not a placebo. More on NSDR protocols for sleep and why you keep waking at 3am.

If you only change three things

For the shortest list on how to increase deep sleep, start with a cool, quiet bedroom and a caffeine cutoff about nine hours before bed. Heat and noise cut deep sleep in lab studies, and caffeine cut it by about 11 minutes in a meta-analysis. Skip alcohol on nights that matter, since it breaks up the second half of the night. Then keep bed and wake times within about 30 minutes either way from night to night, weekends included, as Huberman's newsletter recommends.

FAQ

How much deep sleep do I need?

There's no agreed figure for how much deep sleep you need. Adults typically get 10 to 20% of the night, roughly 40 to 110 minutes, and less with age. The Sleep Foundation suggests going by how you feel in the morning and through the day instead.

Why am I getting so little deep sleep?

You may be getting so little deep sleep because of age, late caffeine, a warm or noisy room, or stress, which the Sleep Foundation links to less deep sleep. Long or late naps can also cut into night-time sleep, so Huberman suggests keeping naps to 30 minutes or less and finishing by early to mid-afternoon. If you snore loudly or wake unrefreshed most days, see a doctor, since a sleep disorder may be the cause.

Can supplements increase deep sleep?

Supplements are the weakest part of how to increase deep sleep, with little evidence behind them. One candidate, magnesium L-threonate, raised brain magnesium in rats. In a 21-day trial of 80 adults aged 35 to 55 with sleep complaints, 1 g a day improved the Oura ring's deep sleep score over placebo. The trial was industry-funded (by AIDP, which also employed three of its authors), and a ring score isn't lab sleep staging. See magnesium threonate for sleep. Check with a doctor before starting any supplement, especially if you take medication, have kidney problems or are pregnant.

Do sleep trackers accurately measure deep sleep?

Sleep trackers measure deep sleep only roughly. In a lab test of seven consumer devices against polysomnography in 34 young adults, they detected sleep well, but their sleep-stage estimates were inconsistent. Watch the trend over weeks, not one night's figure.

Does NSDR increase deep sleep?

NSDR hasn't been shown to increase deep sleep, because no study has recorded overnight sleep after it. The nearest evidence is the small yoga nidra insomnia trial above. NSDR is awake rest, and it doesn't replace sleep.

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