How to get more deep sleep: the few things that move it

The Short Version

Deep sleep responds to a short list of things, and most of them are things to stop doing. Andrew Huberman's answer to a listener who wanted more slow-wave sleep begins with three "don'ts": alcohol, caffeine and cannabis in the 8 to 12 hours before bed, followed by not eating in the last two hours [1]. Matthew Walker's "greatest hits" for deep sleep are a regular schedule, exercise, a cool bedroom and a warm bath or shower before bed, with alcohol as the key thing to avoid [5]. The one well-documented thing to add is exercise: about an hour of fairly hard cardio finished at least six hours before bedtime improved slow-wave sleep in the study Huberman describes [1]. The reason to protect this stage directly is that it carries most of the night's growth hormone release and tissue repair, and it also lowers blood pressure, restocks the immune system, regulates blood sugar and clears waste from the brain [1][2][3]. For anything involving supplements, medication or a medical condition, a doctor's advice comes first [3].

Table of contents

What They Said

What deep sleep is, and when you get it

Huberman uses deep sleep and slow-wave sleep interchangeably; they are not exactly the same, he says, but they fall under the same mechanistic umbrella [1]. Walker gives the formal picture. Non-REM sleep has four stages of increasing depth, and stages three and four are deep non-REM sleep [2]. In those stages the brain slows to one or two cycles per second while the waves become enormous, many times larger than in waking [2]. His analogy is a football stadium: awake, everyone is having separate conversations; in deep sleep, hundreds of thousands of neurons fire together and fall silent together, like a whole crowd chanting in unison, a pattern that appears in no waking state [2].

Both men stress when it happens. Sleep runs in cycles that average about 90 minutes in adults, and the mix within the cycles changes across the night: early cycles are dominated by deep non-REM sleep with little REM, and later cycles by REM as deep sleep fades [2]. Huberman says the same: in roughly the first half of the night most sleep is slow-wave sleep, and that is the typical pattern "when you're not disrupting your sleep architecture with things like caffeine and alcohol" [1].

This timing has a practical consequence that Walker spells out. A short night does not shorten every stage evenly. If you wake very early you lose REM; if you go to bed very late, you mostly get REM and miss much of your deep sleep [4].

Huberman: why it is worth protecting

"During deep sleep, you secrete growth hormone," Huberman says, and "most of that growth hormone release is restricted to the first half of your sleep night" [1]. Growth hormone is involved in metabolism, protein synthesis, muscle repair and the repair of all cell types and tissues [1]. He adds two further functions. Recent research that tracked metabolic factors in people's breath and blood during sleep found the body uses energy very differently in the first half of the night, which matters for regulating insulin and blood glucose during the day [1]. And slow-wave sleep is when the brain clears debris linked to conditions like dementia [1].

In his episode on growth hormone he gives the conditions for the release. Two must be met: "you need to get into slow wave sleep, that's so-called deep sleep and you need blood insulin and glucose to be relatively low" [3]. He also gives the reason to care more with age. Between the ages of 30 and 40, the amount of growth hormone released each night drops two- to threefold, and he says that in his 40s he noticed slower recovery from exercise and wounds even with the same sleep [3].

Walker: what else deep sleep does

Walker's list is longer and reaches beyond repair. The slow waves and sleep spindles appear to send a calming signal to the body, shifting the nervous system toward the parasympathetic rest state, and he calls deep sleep almost the best blood pressure medication you could wish for [2]. It restocks immune defenses such as natural killer cells and T cells and increases the body's sensitivity to immune signals [2]. It regulates blood sugar: when researchers use quiet sounds to strip out deep sleep without waking people, the pancreas releases less insulin and cells respond less to it [2]. It helps move memories from short-term to long-term storage, and it activates a cleansing system that clears beta-amyloid and tau, the proteins involved in Alzheimer's disease [2].

On growth hormone he agrees with Huberman and adds a detail. It is released mainly during sleep, depending both on sleep itself, particularly deep sleep, and on nighttime, so shift workers who sleep by day release less [2].

He also ties deep sleep to anxiety. His team expected REM sleep to be the stage that mattered and found the opposite: "It was deep non-rem sleep." [5] Deep sleep predicted overnight reductions in anxiety, re-engaging the frontal lobe the next day and shifting the body toward calm: "It seems to reduce your heart rate. It seems to drop levels of cortisol." [5]

Walker is careful about one thing. Every stage matters, he says, and none is simply the good one [2].

Huberman's list: the don'ts come first

Asked directly how to increase slow-wave sleep, Huberman says, "First of all, are the don'ts, and then we'll talk about the do's." [1]

Alcohol. One way to really disrupt slow-wave sleep is "to drink alcohol within eight hours prior to bedtime or even at all" [1]. Some people find that even a glass of wine or a beer with lunch reduces their slow-wave sleep, sometimes their REM sleep too, and disrupts their overall sleep architecture [1]. "This has been shown again and again." [1]

Caffeine. He says "avoiding caffeine within eight and ideally within 12 hours of bedtime would be preferable", and that doing so will greatly assist in getting more slow-wave sleep and higher quality REM sleep [1].

Cannabis. He adds THC and CBD to the same list and window: "So that's actually three major don'ts. Avoid caffeine, alcohol and cannabis." [1] Alcohol, cannabis and CBD can help people fall asleep, he notes, but human studies he discussed with Walker show they reduce sleep quality [1].

Late meals. Avoiding food in the two hours before sleep greatly assists growth hormone output early in the night and the depth and duration of slow-wave sleep; three to four hours is even better if you can still fall asleep easily [1]. In the growth hormone episode he is blunter: "eating within two hours of going to sleep is going to suppress growth hormone release. That's very clear." [3] If you do need to eat close to bed, "you wouldn't want to eat anything that would increase blood glucose too much" [3].

He attaches a firm caveat to the meal rule: "if you go to sleep too hungry, it can also disrupt your sleep", and he cannot fall asleep himself when too hungry [1]. He typically eats dinner between 6 and 8 p.m. and sleeps between 10 and 11 p.m.; if he is hungry at 9 p.m., a small amount of food is fine [1]. His priority is explicit: "it's better to make sure that you're getting to sleep than it is to avoid food" just to raise growth hormone output [1].

Huberman's one well-documented "do": exercise, timed

The first tool he calls well documented is a randomized crossover study titled "Exercise Improves the Quality of Slow-wave Sleep by Increasing Slow-wave Stability" [1]. Participants did 60 minutes of exercise at 60 percent of VO2 max, which he places roughly in zone three or zone four: breathing pretty hard but not extremely hard, "relatively challenging cardiovascular output" [1]. They did it at least six hours before bedtime, and in all conditions they abstained from caffeine and alcohol [1]. Measured by EEG, slow-wave sleep was enhanced. "So exercise of this sort turns out to be a very potent form of improving slow-wave sleep." [1]

Three details from the study are worth keeping. The researchers saw no large change in core body temperature, so that could not explain the effect; it appeared to come from changes in the fine structure of the brain waves [1]. The benefit was not felt: "the subjects in this study did not report subjectively feeling that much better from their sleep" [1]. Huberman argues it still matters because of what slow-wave sleep does for body and brain repair [1]. And the study did not test resistance training, though he suspects moderately intense lifting done far enough from bedtime would work similarly [1].

Timing cuts the other way too. Intense exercise within six hours of bed, he notes, can reduce both slow-wave and REM sleep for many people [1].

In the growth hormone episode he describes how a session should be built if the aim is the overnight hormone release. Warm up for about 10 minutes and genuinely raise body temperature, then do weights or endurance work for about 60 to 75 minutes of hard work, getting close to failure without going to it [3]. Done this way, growth hormone rose 300 to 500 percent at rest and again the following night: "It's almost like you're getting a second sleep during the day." [3] Keep blood glucose from being too high, since a sugary sports drink flatlined growth hormone in the studies, and cool down afterward with a cool shower, an ice pack or simply going outside [3]. Sessions that run too long, or body temperature that stays high too long, raise cortisol and eliminate the second overnight rise [3].

Walker's list: regular, active, cool, and no alcohol

Asked for his top tools for deep non-REM sleep, Walker starts with the schedule: "regularity is going to be key here" [5]. A regular schedule reduces fragmentation [5]. In his framework regularity means going to bed and waking at the same times, within about 30 minutes, measured from lights out, and he recommends a bedtime alarm as well as a wake-up alarm [2].

Second is exercise. "Exercise seems to be one of those things that's very good at improving the quality of your deep sleep. And here I'm talking about the electrical quality of your deep sleep." [5] He declines to give an exact prescription of minutes and wattage, advising only that people be physically active to a degree [5].

Third is temperature: "getting your bedroom cool seems to be a way to promote the increase in deep sleep" [5]. The reason, from his first conversation with Huberman, is that we need to drop core temperature by about one degree Celsius to fall and stay asleep [2]. A warm bath or shower before bed is on the same list [5]. He compresses the positive advice into four words: "get regular, get cool" [5].

His key don't is alcohol. Besides compromising REM sleep, "it will fragment your sleep or make your sleep more unstable" [5]. The fragmentation falls especially in the first four hours of the night, when deep sleep dominates, and he adds that alcohol increases anxiety over the long run even though people use it to take the edge off [5]. His general verdict is that "sedation is not sleep.": a nightcap helps you lose consciousness faster, which is different from falling naturally asleep [4]. Even one glass of wine at dinner has measurable effects, and in one study growth hormone release dropped by over 50 percent during alcohol-laced sleep [4].

On caffeine he supplies the mechanism and a number. Caffeine's half-life is about five to six hours and its quarter-life 10 to 12 hours, with individual differences driven by liver enzyme genes [4]. His rule of thumb is to stop roughly 8 to 10 hours before bedtime [4]. The important finding is that falling asleep proves nothing: even people who fall and stay asleep after an evening espresso can lose up to 30 percent of their deep sleep, a drop he compares to aging 10 to 12 years [4]. They wake unrefreshed, drink more coffee, and sometimes use alcohol to come down [4]. He has softened his tone on the subject: "the dose and the timing makes the poison," [4].

Walker adds one more enemy of the early night. Stressful events or news late in the evening raise cortisol and sympathetic activity, producing a tired but wired state, and he avoids stressful content in the late evening for that reason [2].

The supplements: Huberman's stack and Walker's doubts

Huberman is clear that behaviors come first: morning sunlight or bright light, and avoiding bright light between 10 p.m. and 4 a.m. [1]. After that he describes what he takes 30 to 60 minutes before bed: magnesium threonate, which he treats as interchangeable with magnesium bisglycinate, plus apigenin, the compound in chamomile [1]. He warns that people with very intense dreams, sleepwalking or night terrors may want to skip threonate because it can make dreams more vivid and emotional [1]. The addition he highlights is 900 milligrams of myo-inositol, which he takes when eating lower-carb, training hard or going to bed a little hungry; he cites a randomized, double-blind, placebo-controlled study in pregnant women showing improved sleep quality, and says he finds it much easier to fall back asleep after waking in the night [1].

Walker's reading of the evidence is cooler. He finds magnesium's evidence unconvincing except in deficient people, though he is curious about the brain-penetrating threonate form [4]. Valerian failed in five of seven good trials [4]. He calls tart cherry juice and kiwi fruit preliminary but intriguing [4]. His method for testing any supplement on yourself is a month without it, a month on it, and a month off again [4].

On melatonin the two mostly agree. Huberman is not a fan, because many products contain much more or much less than the label states and because it is a potent hormone that affects other hormone systems [1]. Walker cites a meta-analysis in which supplements increased total sleep by about 3.9 minutes and sleep efficiency by 2.2 percent in healthy adults, "a weak sauce effect." [4] He notes that effective doses in studies are around 0.1 to 0.3 milligrams, far below common 5 to 10 milligram tablets, and that one analysis found actual content ranged from 83 percent less to 478 percent more than labeled [4]. Huberman does report one finding specific to deep sleep: a few studies in which very low doses, around 500 micrograms, shifted early-night sleep toward slow-wave activity and improved growth hormone release. "Not a lot of studies, but the ones that I saw are quality." [3]

Where They Agree, and Where They Don't

They agree on the core list. Alcohol is the first or the key "don't" for both [1][5]. Both name exercise as the main positive lever [1][5]. Both stress that deep sleep sits in the early part of the night and that growth hormone depends on it [1][2][3].

They agree that being able to fall asleep is no test. Huberman says alcohol, cannabis and CBD help people fall asleep while lowering sleep quality [1]. Walker says the same of alcohol and shows that an evening espresso can cost deep sleep in people who sleep through the night [4].

They differ slightly on the caffeine window. Huberman says at least 8 and ideally 12 hours [1]. Walker says roughly 8 to 10 [4]. Walker's own figure for caffeine's quarter-life, 10 to 12 hours, explains why the longer end is defensible, and he notes that people differ genetically in how fast they clear it [4].

They differ on how exact to be about exercise. Huberman offers a specific protocol from one study, 60 minutes at 60 percent of VO2 max at least six hours before bed [1]. Walker will not prescribe a dose at all [5]. Huberman is reporting a single trial, and Walker is describing what the wider evidence supports as a general statement; the two are compatible.

They differ on cannabis and CBD. Huberman puts THC and CBD together on the avoid list [1]. Walker says THC speeds the onset of unconsciousness and blocks REM sleep, but calls the CBD picture less clear: low doses around 5 to 10 milligrams may promote wakefulness, while above roughly 25 milligrams some studies show more sleepiness, and purity is a concern [4]. Huberman's inclusion of CBD is the more cautious rule, and Walker's is the more detailed account of mixed data.

They differ on supplements. Huberman uses magnesium, apigenin and myo-inositol and reports benefits in his own sleep and tracker data [1]. Walker finds the magnesium evidence weak outside deficiency [4]. Huberman's evidence here is largely personal, plus one trial in pregnant women, and he presents it as optional after behaviors [1].

Their lists emphasize different things. Huberman's answer centers on substances, meal timing and one exercise study [1]. Walker's centers on regularity and temperature [5]. Neither contradicts the other, and the full list comes from combining them.

On growth hormone and sleep stage there is one loose thread. Huberman ties the release to slow-wave sleep and delta waves [1][3], and Walker ties it to sleep and particularly deep sleep [2]. The summary of one Walker conversation also says growth hormone release is tied to REM, without elaboration [4]. The weight of what both say, in detail, is on deep sleep.

Why It Works

Slow waves trigger the hormone. Huberman's explanation of why growth hormone comes in deep sleep is specific: "So the answer is it's delta wave activity in the brain." [3] The big slow waves drive the growth hormone releasing hormone neurons that signal the pituitary [3]. Studies in sleep-deprived people show the release is not simply a 24-hour pulse: "it's always relating to slow wave deep sleep and delta waves" [3].

Insulin and glucose block it. The second condition for release is low blood insulin and glucose, which is why a meal within two hours of sleep suppresses it [3].

Caffeine hides sleep pressure. Adenosine builds up the longer we are awake and creates the pressure to sleep; caffeine blocks its receptors, so the brain cannot register how long it has been awake [4]. With a quarter-life of 10 to 12 hours, a meaningful share of an afternoon dose is still active at bedtime [4].

Alcohol sedates and then fragments. It activates the fight-or-flight system and breaks sleep up, most of all in the first four hours where deep sleep is concentrated [4][5].

The body has to cool. A drop of about one degree Celsius in core temperature is needed to fall and stay asleep, which is the logic behind a cool room [2].

Regularity reduces fragmentation, and deep sleep is counted by its continuity and power. Walker says a regular schedule reduces fragmentation [5]. In the lab, sleep quality is measured partly by the electrical power of deep sleep, and quality predicts health about as strongly as quantity [2]. In a UK Biobank study of more than 60,000 people, the most regular sleepers had a 49 percent lower risk of dying from any cause than the most irregular, and regularity predicted mortality even more strongly than duration [2].

Exercise changes the waves themselves. In the study Huberman describes, the gain was in slow-wave stability, the amount of power present in slow-wave sleep, and not in body temperature [1]. Walker's phrase for the same thing is the electrical quality of deep sleep [5].

Deep sleep is restorative in a literal sense. The brain is less metabolically active in deep sleep, and seven to nine hours of sleep, especially deep sleep, clear the adenosine that built up during the day [2].

Where It Applies, and Where It Doesn't

Your tracker is guessing. Huberman answers the listener's question with an asterisk: consumer devices estimate sleep stages from heart rate, heart rate variability and movement, and whatever the device, "It is an estimate or a best guess at what stage of sleep you're in." [1] Sleep laboratories use EEG, EMG and direct observation of eye movements [1]. A reading of 10 percent deep sleep is a reason to look at habits, not a diagnosis.

The ratio is not a known danger. Asked whether more REM and less deep sleep is harmful, Huberman says it is not clear that it causes specific health problems, and he could not find studies of the ratio itself [1]. Less slow-wave sleep could plausibly impair recovery from exercise or injury and perhaps immune function [1]. His advice is to aim for rough balance without obsessing over percentages: "Your body is much more resilient than that." [1]

Deep sleep is not the only stage that counts. Walker insists none is simply the good one [2]. REM, concentrated late in the night, does its own work on emotion and memory, and the same alcohol and THC that harm deep sleep also suppress REM [4][5].

Total sleep comes first. With only four or five hours, balance between the stages is unlikely; Huberman suggests at least six and ideally seven to eight hours for about 95 percent of people, and Walker says seven to nine for most adults [1][2].

The meal rule bends. If going to bed hungry keeps you awake, eat something small; getting to sleep matters more than the extra growth hormone [1].

One bad night is not a crisis. Walker repeatedly reassures listeners that the concern is chronic short sleep [2]. His advice after a bad night is to do nothing: do not sleep in, nap, add caffeine or go to bed early, since all of those undermine the next night [4]. That protects the regularity his deep-sleep list starts with.

Persistent trouble is a medical matter. Lying awake more than about 20 to 25 minutes, or waking consciously many times a night, are the red flags Walker names [4]. Snoring and sleep apnea, where the airway collapses and breathing stops, are a separate cause of poor sleep [2]. For insomnia he says cognitive behavioral therapy works as well as sleeping pills in the short term and better in the long run [4]. These call for a clinician. So do supplements, hormones and heat exposure: Huberman's instruction is to "talk to a doctor before you do anything" [3]. He describes sauna as a powerful stimulus for growth hormone while awake, and is emphatic that overheating is dangerous [3].

What To Do With It

1. Stop alcohol at least eight hours before bed, or skip it. Both experts put it first, and even a drink at lunch or dinner has measurable effects in some people [1][4][5].

2. Have your last caffeine 8 to 12 hours before bedtime. For an 11 p.m. bedtime that means late morning to early afternoon. Do not use the fact that you can still fall asleep as evidence that it is harmless [1][4].

3. Keep cannabis, including CBD, out of the same window if deep sleep is the goal. Huberman lists it with alcohol and caffeine; Walker regards the CBD evidence as unsettled [1][4].

4. Finish dinner at least two hours before sleep, three to four if you can. Keep any late snack small and low in sugar, and eat something if hunger would otherwise keep you awake [1][3].

5. Go to bed and get up at the same times, within about 30 minutes, including weekends. Set a bedtime alarm. A very late bedtime costs deep sleep in particular [2][4][5].

6. Exercise most days, and finish hard sessions at least six hours before bed. The studied dose is 60 minutes of fairly hard cardio; a warm-up, about an hour of work short of failure, and a cool-down is the pattern Huberman describes for growth hormone [1][3].

7. Cool the bedroom, and take a warm bath or shower before bed. Both are on Walker's short list for deep sleep [5].

8. Keep the late evening calm. Walker avoids stressful content late at night because it raises cortisol [2].

9. Change one thing at a time. Huberman's advice is "trying various things one by one to see what works best for you", and Walker's month off, month on, month off test applies to any supplement [1][4].

10. Judge by how you function, and get help if problems persist. Treat tracker stages as estimates, watch for daytime sleepiness, and see a doctor about long wakeful stretches, snoring or anything involving supplements or medication [1][3][4].

Sources

1. AMA #2: Improve Sleep, Reduce Sugar Cravings, Optimal Protein Intake, Stretching Frequency & More · Huberman Lab
2. Dr. Matt Walker: The Biology of Sleep & Your Unique Sleep Needs · Huberman Lab
3. How Thyroid Hormone and Growth Hormone Control Your Metabolism, and How to Support Both · Huberman Lab
4. Dr. Matt Walker on Perfecting Your Sleep: Sleep Stages, Caffeine, Alcohol, Supplements, Naps and Unconventional Tips · Huberman Lab
5. Dr. Matt Walker: Improve Sleep to Boost Mood & Emotional Regulation · Huberman Lab