#145 - How to get More Deep Sleep

0:02Matt Walker: Hi there, it's Matt here, and welcome back to the podcast. If I had to name the question I get asked more than any other, stopped on the street at the end of a lecture, in the comments underneath, just about everything I post online, it would be some version of this. How do I get more deep sleep? How do I boost my deep non-rapid eye movement sleep or push up that deep sleep score my watch shows me every morning? It's a fair question to ask, but let me offer one small caveat right at the start, because I think it matters. Deep sleep is not the most important stage, and it isn't the best one. Your dreaming rapid eye movement sleep and even the lighter stage 2 non-rapid eye movement sleep are every bit as important.

0:48Matt Walker: They simply do different jobs for your brain and body at different times of the night. So this isn't about chasing one stage at the expense of the others. It's just that deep sleep is the one people ask me about most, and the one doing a particular kind of quiet, heavy maintenance overnight. So tonight, that's where we'll gently put our attention. And the good news is that almost everything which moves it comes down to fairly ordinary things you do tonight. No gadgets to buy, no machines from a laboratory, things already within your reach. most of them free, and each one backed by a number I can hand you as we go.

1:28Matt Walker: Before the answer, though, let me show you the strangest way to get more deep sleep. And I'm sharing it mostly so you'll know never to use it. Stay up all night, properly, no sleep at all. And the following night, your brain will sleep deeper than usual. Not longer, deeper. The slow, heavy delta waves roll harder and thicker than they have in weeks, which sounds on the face of it like a wonderful shortcut. It isn't one. And understanding why tells you almost everything about how deep sleep actually works. That rebound is simply the sound of a debt being repaid. All day while you're awake, a molecule called adenosine builds up in the brain.

2:12Matt Walker: Adenosine is one of the great signals of sleep pressure. The longer you're up, the more it piles on. The heavier the eyelids, the greater the push towards sleep. When you finally lie down, the brain settles that pressure first, and it pays in the currency of deep, non-rapid eye movement sleep. Deprive yourself, and the bill comes due with interest. But chronic short sleep doesn't just collect the interest, it fragments the night, unsettles the metabolism, and slowly wears down the very systems deep sleep exists to restore. Sleep deprivation isn't a protocol. It behaves a little more like a loan shark.

2:53Matt Walker: So here's how I want to lay this out. I'm going to give you two lists. First, the things to lean into and do more of, the builders. Then, the things to do less of or abstain from, the saboteurs. And one thread ties the whole night together. Deep sleep is fragile. It thins with age and it is front-loaded. Most of your night supply arrives in the first two or three cycles, the couple of hours right after you fall asleep. Think of it as a tide that comes in hardest at the very start of the night. Disturb those first hours and the water never quite rises that high again. Protect the front of the night and you've done most of the work.

3:39Matt Walker: Start with what may be the biggest lever of all and the one most of us overlook, regularity. Deep sleep is built on sleep pressure. Sleep pressure is organized by a clock, and a clock only works if it's kept. In a healthy adult, slow-wave sleep makes up somewhere around 13 to 23 % of the night, weighted heavily toward the beginning. But that architecture assumes a body that knows when night is coming. Let your bedtime drift by a couple of hours, and the signal blurs, and the brain stops laying down its deep sleep in those clean early blocks. So pick a wake time and try to hold it, weekends included.

4:22Matt Walker: And give yourself a genuine 7-9 hour window. That one habit will quietly do more for your deep sleep than anything you can swallow, plug in or strap to your head. The takeaway, a steady wake time and a full 7-9 hour window. Next, the daytime lever, move your body. Exercise raises sleep pressure, steadies the circadian rhythm and helps the body handle its own temperature. Pool the controlled trials and regular movement improves sleep quality, shortens the time it takes to fall asleep and can lift slow wave sleep itself. Aim for a couple of hundred minutes of moderate movement across the week with a little resistance training.

5:04Matt Walker: The old rule to keep all exercise far from bedtime has softened. On average, evening exercise doesn't seem to harm sleep and can even nudge deep sleep upward with one exception. Vigorous, heart-pounding effort in the final hour before bed, which can push sleep onset back. So it's usually enough to finish the hard work an hour or more before lights out. The takeaway, move your body most days and leave the hardest efforts at least an hour before bed.

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7:28Matt Walker: Then, the loveliest move of the night, and it's a gentle paradox. To cool the brain for deep sleep, you warm the body first. As sleep approaches, your core temperature has to fall, and that fall is part of the machinery that starts and holds the deep stage. In fact, your core temperature reliably begins to drop about two hours before you fall asleep. And that first bout of deep non-rapid eye movement sleep tends to land right at the steepest point of that temperature slide. A warm bath or shower opens the blood vessels at the skin surface. And when you step out, your body sheds heat through that open skin and your core temperature drops further and faster than it would have alone.

8:17Matt Walker: It's rather like throwing open the windows of an overheated house. The warmth rushes out through the skin and the core at last cools. The hot bath quietly is really a cooling device and it has been measured again and again. Pool the controlled trials of before bed water heating and warming yourself in water of around 40 to 42.5 degrees Celsius, that's 104 to 109 Fahrenheit, one to two hours before bed for as little as 10 minutes significantly shortens the time it takes people to fall asleep. And the window is more forgiving than people assume. Across the wider literature, warming the body anywhere from one to eight hours before bed reliably increases slow-wave sleep and deepens your non-rapid eye movement sleep.

9:11Matt Walker: You don't even need much of a temperature shift for the brain to notice. In one exquisite experiment, researchers raised people's skin temperature by just 0.4 of a single degree Celsius, an amount you'd never consciously feel. And in older adults, that whisper of warmth almost doubled the proportion of slow-wave sleep and drop the chance of waking too early in the morning from 58 % to 4%. And here's a detail that reframes the whole thing. The best predictor of how fast you fall asleep isn't the room. It's whether the blood vessels in your hands and feet have opened to let heat escape. Warm feet, in the title of One Paper in Nature, promote the rapid onset of sleep.

9:58Matt Walker: In newborns, a wide enough temperature gradient from the core out to the skin made them three times more likely to fall asleep within half an hour. So this is why the old advice about socks in bed actually holds up. Warm feet help the core shed heat. Then, once you're warm, let the room itself be cool. Somewhere in the mid-60s Fahrenheit, around 18 to 20 degrees Celsius, with breathable bedding, the takeaway? A warm bath one to two hours before bed, warm feet, then a cool dark room. Light works right alongside temperature because deep sleep is strongest when the circadian rhythm is strong. And light is the master dial that sets it.

10:43Matt Walker: Researchers once tracked melatonin, the hormone that announces biological night. Ordinary room light under 200 lux, the kind of glow you're very likely sitting in right now pushed the rise of melatonin later in 99 % of people. And it shortened the hormone's nightly window by about 90 minutes. And sleeping with even a faint light left on in the room measurably lowers deep slow-wave sleep and raises nighttime arousals. So do two small free things. In the last hour or two before bed, dim everything. And in the morning, do the opposite. Get outdoors into daylight in the first hour after waking. Bright mornings, dim evenings.

11:24Matt Walker: Food moves the needle more than most of us expect, and the timescale is the surprising part. It isn't your diet over years, it's what you ate today. In one crossover study, healthy adults were fed a controlled diet and then for one day allowed to eat freely. The more fiber a person ate, the more deep slow-wave sleep they got. The more saturated fat, the less of it. And the more sugar, the more often they surfaced into fragmenting arousals. Timing matters too. In another study, a carbohydrate-rich meal eaten four hours before bed cut the time it took people to fall asleep from 17.5 minutes to 9, a 49 % reduction, almost in half.

12:10Matt Walker: But the very same meal, eaten just one hour before bed, lost most of that benefit. And remember why falling asleep faster matters here. Deep sleep is front-loaded, so every minute you save at the start of the night is a minute of that early, deep, rich window you actually get to keep. The takeaway, favor fiber over saturated fat and sugar and finish your main meal a few hours before bed. Now one you might not expect on a sleep podcast, sex and intimacy before bed. and before a single number, I want to say something plainly and mean it. Yes, in the data, it is the orgasm that appears to be the active ingredient, the piece most tightly linked to the improvement in people's sleep.

12:59Matt Walker: But I am not saying that intimacy has to be about reaching orgasm. Sex and closeness do not need orgasm as their central goal or their finish line. The connection, the touch, the simple calm of being close to another person that carries its own worth entirely apart from where it does or doesn't lead. So please take the orgasm finding as useful information, not as a target you must hit. With that said, here is what the data show. In one survey of nearly 800 adults, 71 % said that sex with a partner ending in orgasm improved their sleep, and only 3-6 % said it made sleep worse. Solo also counted as masturbation with orgasm improved sleep for 54%.

13:50Matt Walker: Now, an honest asterisk on those numbers. These studies measured the subjective quality, not deep non-rapid eye movement sleep, traced directly on an electrode, and yet it isn't a reckless leap to join the two together. When you line up how people rate a night's sleep against what the electrodes actually recorded, the depth of that sleep keeps surfacing near the top of the list. It isn't unanimous across every study, I should say, but it's a fair evidence-guided bet that at least part of what people are feeling is deeper sleep. The likely machinery is a gentle post-orgasm neurochemical wash, oxytocin up, the stress hormone cortisol down, and a rise in prolactin, a naturally sedating hormone.

14:37Matt Walker: The takeaway Intimacy before bed is a genuine free wind down, and the closeness matters as much as the finish. And do give the mind a runway. Arousal is deep sleep's quiet enemy. A racing head will hold your brain out of stable slow-wave sleep, no matter how dark and cool the room is. So build a small buffer, a protected half hour between the day and the bed, 10 or 20 minutes of slow breathing, a body scan, a few pages of a paper book under low light. The particular practice matters far less than simply doing it. You're offering the brain a slope instead of a cliff. The takeaway, give your mind a buffer, a gentle slope into sleep, not a cliff.

15:23Matt Walker: And the most important do of all, treat the two conditions that undo everything else. If you snore loudly, wake gasping or feel unrefreshed after a full night in bed, please get evaluated for sleep apnea because an airway that keeps closing pulls your brain up out of the deep water hundreds of times a night and no bath or supplement will fix that. And if you lie awake with chronic insomnia, the strongest tool we have isn't a pill. It's cognitive behavioral therapy for insomnia, which retrains the brain to sleep efficiently and unlike sedatives, can genuinely rebuild your deep sleep. Those two aren't the alternative option.

16:06Matt Walker: They're the first one. The takeaway, if apnea or insomnia is in the picture, treat it first. It outranks everything else here.

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17:39Matt Walker: now we'll turn to the saboteurs let's start with the drug most of us reach for without a second thought caffeine it's a wonderful thing if you want to be awake and rather less wonderful if you want deep sleep because of how it works it doesn't drain your sleep pressure it simply blocks the receptors that let your brain feel it the pressure is still there you've just unplugged the gauge and it lingers with a half-life of about five to seven hours in most of us. There's one study I keep coming back to and it may change your afternoon. Researchers gave people 400 milligrams of caffeine, think a couple of strong coffees, at three different times, right at bedtime, three hours before bed and a full six hours before bed, double blind, placebo controlled with a monitor recording each night, and the finding is a quietly sobering one.

18:35Matt Walker: At every single timing, caffeine cut total sleep by more than an hour, somewhere between 66 and 72 minutes, compared with placebo, not just at bedtime. Even the dose taken six hours before bed, the one you'd assume had worn off, still cost more than an hour of sleep, and measurably reduced slow-wave sleep. Sit with that for a moment. A coffee at 2 or 3 in the afternoon may still be close enough to bedtime to shallow your deepest sleep, so it's worth setting yourself a curfew. For most people, nothing after early afternoon, earlier if you're sensitive, anxious, older, pregnant, or a slow metabolizer.

19:16Matt Walker: And do remember, it hides in a great many places. Tea, soda, energy drinks, pre-workout, chocolate, even some painkillers. The takeaway, set a caffeine curfew. For most of us, nothing after early afternoon. Now to the one I get asked about most, alcohol. And alcohol is perhaps the great impersonator of sleep. Here is the trick it plays. Pool every controlled study of alcohol in healthy sleepers. And at every dose, a drink does three things. It helps you fall asleep a little faster. It makes the first half of your night look calmer and more consolidated, and then it quietly wrecks the second half.

20:00Matt Walker: So the person who swears their nightcap works is telling the truth about the first half of the film. They're just not seeing the second. Now let me give you the three dials that decide how bad it gets. The first dial is dose, and it's close to a straight line. A genuinely small amount, think blood alcohol around 0.03%, a single drink, may barely register on the sleep of a healthy person. But push it up towards 0.10 % and alcohol starts behaving like a short-acting sleeping pill in the first half, followed by a rebound of lighter, broken sleep as your body clears it. And it delays your first dream sleep of the night at every dose, suppressing more and more REM the higher you go.

20:45Matt Walker: The second dial is timing. You might assume that if you finish your drink early, you're safe. Not quite. In one study, people were given alcohol a full six hours before bed. By the time they lay down, a breathalyzer read exactly zero. Every last molecule metabolized, gone. And yet the sleep was still disrupted. Wakefulness in the second half of the night doubled. The disruption outlived the drink. Earlier is less bad than later, yes. The same dose taken close to bedtime within an hour hammers the front of your night far harder than a dose taken several hours earlier. But earlier is not the same as harmless.

21:24Matt Walker: And the third dial is the one people most want a loophole on. The type of drink. Wine, beer, spirits, the expensive stuff, the organic stuff. I'm sorry to report there's no loophole here. It's the ethanol that does this, not the beverage. No wine, no beer, no spirit has been shown to be kinder to your sleep. Now let me show you what alcohol is doing underneath the surface, because this is where it stops being about grogginess and starts being about your body. Start with the heart, even at moderate amounts, below what anyone would call heavy drinking. Evening alcohol speeds your heart rate all night.

22:04Matt Walker: In one careful dose response study, a low dose ran the nighttime heart about 4 % faster than an alcohol-free night, and a higher dose ran it about 14 % faster. At the same time, it suppressed the calming, vagal break on the heart, blunted the reflexes that steady your blood pressure, and tipped the body toward its stress branch, the sympathetic side. And in women, blood pressure climbed in the early morning hours. We often call sleep a cardiovascular holiday, the one long stretch where the heart gets to rest. Alcohol cancels the holiday. And deep, non-rapid eye movement sleep is meant to be the calmest cardiovascular window of the entire day.

22:48Matt Walker: So this lands squarely on the deep stage. Then there's the hormone. Alcohol suppresses the night's release of growth hormone, your overnight repair crew, by around 70 to 75 percent, while leaving the stress hormone cortisol untouched. And that great pulse of growth hormone isn't released at random. It rides on the back of your first deep non-rapid eye movement cycle. So a 70 % fall is in effect a receipt for deep sleep that was chemically muffled. And then there's your memory. In a study of learning and sleep, a drink before bed cut the dream sleep of the first half of the night sharply. The minutes of rapid eye movement sleep fell by anywhere from around 70 % to over 90%.

23:36Matt Walker: And that rapid eye movement sleep turned out to be doing something. People who learned a task and then drank alcohol even two nights later still lost the memory because the alcohol robbed them of the rapid eye movement sleep that would have cemented it into place days after the lesson. The drink didn't just cost them a night, it reached back and erased the learning. So put the three dials together, dose, timing, type, and the guidance is simple. If you drink, keep the amount modest, finish three to four hours before bed rather than right before, and know that no type of drink buys you a pass. And if you want the best deep sleep you're capable of, keep the alcohol out of the evening altogether.

24:24together.

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26:07Matt Walker: Then there's the one many of you are quietly wondering about, cannabis. And the honest picture is a little more disappointing than the marketing. THC can help you fall asleep, and for a night or two, it may even lift deep sleep. But tolerance builds within about a week, and then it turns, suppressing dream sleep and fragmenting the night. The largest real-world study of its kind followed more than 2 ,000 patients on prescribed medical cannabis, many of them specifically for insomnia over three months. Their pain, anxiety, fatigue, and overall quality of life all improved. And their sleep? On the standard sleep disturbance scale, it barely moved, essentially no change at all.

26:55Matt Walker: The one thing most of them came for was the one thing that didn't budge. As for CBD, at the low doses in most gummies, it's more likely to do nothing than to help. In a placebo-controlled crossover, researchers gave THC together with CBD, and the CBD didn't deepen sleep. It did the opposite. At the higher dose, 15 mg of THC with 15 of CBD, the time spent awake in the night, rose from about 17 minutes to 41. That's a 140 % jump, more than double. And rapid eye movement sleep fell by around a quarter. The takeaway, and it's a caution, don't rely on THC or CBD to build your deep sleep. And last on the less list, the gadgets, the pills, and the supplement shelf.

27:47Matt Walker: There's a real frontier where scientists amplify slow waves directly, with weak currents through the scalp or precisely timed sounds. In the laboratory, it works, but for now, it belongs in the laboratory. and the same goes for the consumer headbands chasing it. There are prescription drugs that raise slow wave sleep and they belong with a physician and a reason. And the sedation of an old sleeping pill is not the same as real natural deep sleep. Being unconscious is not the same as sleeping deeply. Even the supplements, glycine or magnesium, if you're genuinely deficient, sit near the bottom of the list with small effects next to the giants.

28:29Matt Walker: If your magnesium is already normal and you take more, you're mostly just paying for rather expensive urine. The takeaway, leave the gadgets, the pills and the supplement shelf until last. So let's add it all up. First, the things to lean into and do more of. One, regularity, a steady wake time and a full seven to nine hour window. Let the brain lay down its deep sleep in clean front-loaded blocks, the richest 13 to 23 % of the night. Two, exercise, moving most days. Regular training can raise your slow wave sleep. As long as you leave the hardest efforts an hour before bed. Three, warm bath and warm feet.

29:13Matt Walker: One to two hours before bed into a cool room. Gentle warming nearly doubled deep sleep in older adults and cut early morning waking from 58 % to 4%. 4. Light, bright mornings, dim evenings. Ordinary room light delays melatonin in 99 % of people and darkness protects the deep sleep it erodes. 5. Food, fiber over saturated fat and sugar. Main meal a few hours out, more fiber tracks with more deep sleep. and a meal four hours before bed had people asleep about 49 % faster. Six, sex and intimacy. A pre-sleep orgasm links to better sleep in 71 % of people, though the closeness is worth just as much as the finish.

30:02Matt Walker: Seven, winding down. A protected half hour that lowers the arousal, which otherwise keeps you out of the deep stage. Eight, apnea and insomnia, treated first. The therapy for insomnia rebuilds deep sleep a pill can't, and a blocked airway can pull you out of the deep stage hundreds of times a night. And the things to do less of or abstain from. 9. Caffeine. A curfew by early afternoon, even 6 hours before bed, 400mg, cost more than an hour of sleep and cut slow-wave sleep. 10. Alcohol, less of it, and finished 3-4 hours earlier. Alcohol speeds the heart up 14 % all night, cuts growth hormone 70-75%, and can strip 70-90 % of your first half dream sleep.

30:57Matt Walker: And no type of drink is kinder. 11. Cannabis, not to be leaned on. THC and CBD failed to build deep sleep. And a mix of the two more than doubled nighttime wakefulness. Deep sleep is not something you force. It's something you allow. It emerges when the pressure is high, the clock is steady, the body is cooling, the room is dark, the airway is open, and the mind is quiet. In that sense, it's less a switch than a garden. You can't shout at a garden to grow. You prepare the soil, pull the weeds, and give it water and light and darkness in the right amounts. And then, if you've done your part, growth simply happens.

31:40Matt Walker: That's your brain's nightly restoration program. Memories stabilized, the body repaired, the metabolic ledger reset, the cleaning crew let in. Improve it, and you aren't only improving the night, you're improving the next day's brain. And quietly, over the years, perhaps the next decades. Thanks so much for listening. I really do appreciate you giving me your time and your ears. Look after yourself. Enjoy every one of your waking hours. And when tonight comes, I hope it brings you the deepest, soundest sleep you're capable of. Bye for now.