Experts Answered Every Question We’ve Ever Had About Sleep

Every few months I say to myself, with urgency, I need to do better on sleep. It's one aspect of health that can easily fall to the side, because "There's just not enough time!" I protest. How can I do all the things I want and get eight hours? Does anyone get a full eight hours? Does it really matter?

Maybe, like me, you don't sleep enough, and worry about it. Maybe you sleep a little during the week and all day on the weekends because of your work schedule, and wonder if that's ok. Or you're curious about whether to get that organic melatonin in the Whole Foods supplement aisle. We’ve all experienced (or are experiencing) sleep deprivation. I know that when I'm not sleeping well, it affects how I think, how able I am to concentrate, and I feel more run down. I've had a rocky relationship with sleep, but despite being told over and over that I shouldn't look at my phone before bedtime, I still have a lot of questions.

I asked four sleep experts some questions that get beyond the basics, and dig into what sleep is and what it's doing for us. Bryce Mander, an assistant professor at UC Irvine in the psychiatry department, James Wyatt, the director of sleep disorders and sleep-wake research at Rush University Medical Center, Colin Epsie, a professor of Sleep Medicine at the University of Oxford, and Chris Harvey, a sleep scientist at the University of Oxford, weighed in on all topics sleep related.

Credit: Lia Kantrowitz

Short sleep on a regular basis can affect a whole lot more than your mind: It can interfere with the regulation of your hormone cycles, the regulation of your metabolism, or how your immune system responds to challenges. Sleep is critical, not just for your brain, but for your body as a whole.

There are people who legitimately perform well on a short amount of sleep, Mander says. They’re called true short sleepers. “We haven't measured people like that thoroughly enough to know if they truly function well on that amount of sleep across the board,” he tells me. “ But we know that on cognitive tests, or on one certain measure of their health, they're doing fine.”

They’re also extremely rare. If you tried to estimate how many short sleepers there were in a population, and rounded that to the nearest whole number, it would be zero. So with the caveat that they do exist, Mander says that most people who claim this are wrong.

Wyatt agrees: “I don't believe the person who says they only need four or five hours of sleep. I can test them and prove that they need more than that,” he says.

They might feel like they’re functioning fine, or aren’t sleepy, because the awareness that you're not fine depends on the type of sleep loss you're getting. Let’s say a person stays up all night. They would be really tired, and would admit they needed sleep. This sleep-deprived person would perform badly on a battery of cognitive tests.

If you limit that same person to just four to six hours a night for a few weeks, and then measured their performance, they will perform as badly as if they lost an entire night or two of sleep. But a person who is losing just a few hours a night won’t realize this; they will subjectively say they're fine.

“What happens is their subjective ratings of sleepiness goes up and then plateaus because it's become their new normal,” Mander says. “They're adjusted to it, so to speak. But their objective performance continues to worsen. It's completely disconnected from their own ability to rate themselves.”

This is dangerous because most of us who aren’t in college anymore don’t pull all nighters. Instead, we do the kind of chronic restriction that is hurting our everyday lives and that we’re not aware of.

If you’re still thinking that’s not you, and you’re fine, Mander has a dare: “Anyone who says that, come into our lab, we'll test you. We'll show you you're not.”

The circadian rhythm is the 24-hour physiological pattern that your body follows, which is regulated by an internal biological clock and cues from the environment (like the sun). But within this, people can still show differences in the times they get sleepy, or wake up. This is called your chronotype.

“A lot of people misunderstand the alignment of the circadian cycle to the light-dark cycle with chronotype, or phase preference,” Mander says. “A subtle point, but it's an important point.”

Here’s the difference: Your clock adjusts itself to a 24-hour cycle in a particular way. It thinks: Light means it’s day, dark means it’s night. I should be awake during the day, and asleep during the night, so I’ll organize the body’s various functions accordingly. But the specific time a person says, “I’m sleepy and going to bed now,” or “I am awake and going to get up,” can be different from person to person. There are so-called larks and owls, and whether you are one or the other is mostly genetically determined. (Besides owls and larks, some people have true circadian rhythm disorders, which are extreme sleep patterns that are totally out of whack.)

Mander says that larks and owls are pretty evenly distributed, and some argue that there’s an evolutionary reason for that: It was probably advantageous to have some people who are up earlier and others up late, for hunting or keeping watch.

The majority of us are fall somewhere in the mild-lark type through mild-owl type range, Wyatt says and these chronotypes probably aren’t extreme enough to need to do much. Many will naturally fit the nine-to-five schedule pretty closely. This is a big issue is for shift workers, or people who work overnight jobs. “Nobody, really, is the chronotype of: I work in the middle of the night, and I'm not awake through the day,” Mander says.

One of the biggest issues for shift workers is the commute home, when they’re exposed to all the light. I remember working an overnight shift at a newspaper, even just for a week, and the walk home from the office made my body feel like it was time to get up—though I had been awake all night.

Mander says that a classic study from Fred Turek at Northwestern University found in animals that it only takes one second of light for your clock to start adjusting to daytime. “It just shows how sensitive that system is at certain times of the day," he tells me. "There are certain times of the day where light won't affect your clock. If your clock thinks it's daylight and sun is out, it's not going to affect your clock. It'll go, 'Yep, that's what I expect.' It's really between the hours of dusk and dawn, when the internal clock doesn’t expect there to be any light, that it’s really sensitive. The more unexpected the light is, the more the clock will shift in response to it. For example, light at 2 AM will shift the clock more hours than light at 9PM. "

There are some people who deal with work at odd hours better than others. If you’re a morning lark doing shift work, you may be more vulnerable to the physiological and cognitive impairments that come with that. Owls might be better suited to staying up late in that way.

Mander also tells me that delayed types, the owls, are more likely to have comorbid psychiatric disorders related to emotional regulation, like anxiety disorders or depression, whether or not they do shift work. “Not that that chronotype causes it, necessarily, but you're a greater risk if you're at that chronotype,” he says. There could be both biological and social explanations. “If you're a late type, everybody's in bed, everything's closed, you're sleeping in past morning hours, and you're asleep in the morning. So you might be socially isolating yourself a little bit more than if you were a morning type."

Within each chronotype there are also people who are more easily able to switch and sleep at time they don’t necessarily prefer, and others who have a really hard time. “There are some people who critically just can't adjust, to the point where they're just losing sleep, or they miss social engagements and work responsibilities because they cannot adjust their clock,” Mander says.

Maybe. If you think you’re someone who has a hard time sleeping if it’s not on your preferred schedule, and you have a flexible work environment, it doesn’t hurt to ask. If you’re a shift worker, try to minimize your exposure to light, especially around dawn when you’re getting home, and talk to a doctor about your sleep if you’re having trouble.

One group of people we do need to advocate for, the experts say, is teenagers. We all have different chronotypes, and those preferences shifts across our life span. It’s biologically determined, but also related to puberty and hormonal regulation. Mander says it’s been widely shown that there’s a shift when you hit adolescence: The circadian clock becomes a bit more delayed, so teens want to stay up later and get up later. “We don't know why that is, per se. We don't know what the advantage of that is," he tells me. "But it just happens, and then after it happens, after adolescence, it starts to then advance again, and it becomes more normal in young adulthood, and then eventually you become more of a lark as you get older.”

The problem is that high school starts early, at 7 or 8 AM. “It's causing massive sleep loss in our teenagers," Mander says. "It's causing car accidents. It's causing poor performance in schools, behavioral acting out, people saying they're so tired they feel sick and they skip school."

Later school start times could lead to better grades, less car crashes, and less sickness and infection. In California, where he lives, there was recently a bill that would prevent high schools from starting earlier than 8:30, but it was rejected. “That was rather unfortunate," he says, "Because you're basically affecting the ability of kids to learn because you want to have control over your local regulation of your student.”

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Espie asks me: how would I know what size shoe I am? Of course, you would try them on. Same goes for sleep. The best way to find find out the amount of sleep you need is trial and error. Practice giving yourself different patterns, different times of sleep. Once you find out how much sleep you actually need, then try to stick to that pattern.

“What people tend to do with sleep is, unlike their shoes, they cram their sleep into the wrong size,” Epsie says. “That’s when you end up with sore feet.”

Harvey says another way you can tell if you’re chronically sleep deprived is if you’re sleeping in on the weekends. This could mean you’re not getting enough sleep during the week, or not meeting your specific sleep needs.

He recommends taking a couple weeks off and seeing how your sleep pattern naturally falls without any alarms or external pressures to get up and go to bed at a certain time. The first week, you’ll be recovering from any sleep deprivation, but the next week you’ll get an idea of what your body naturally needs. “But it's hard to do that,” he admits. “Not everyone can just take two weeks off work.”

There are three stages of non-REM sleep, Harvey tells me, and each stage has its own electrical signal in the brain that can been seen on a electroencephalogram, which measures the electrical activity in the brain.

Stage one is very early, shallow sleep. Your body is starting to relax, and you feel drowsy; your brain waves and muscle activity are slowing down. Stage two is probably the point in sleep where someone would acknowledge that they are asleep (if you woke them up). Brain activity called spindles can be seen on the EEG, which are rapid bursts of high frequency brain waves, as well as activity called K-complexes, a high amplitude spike of brain activity that might be involved with shutting out external noise or visual inputs.

Then you have stage three—which used to be considered two stages, three and four—which are both now considered deep sleep. This stages are important for memory consolidation and for learning. On an EEG, you would see something called slow waves or slow oscillations, slow continuous brain activity. “This deep sleep is characterized by these certain kinds of wave formations,” Epsie says. “The whole brain activity becomes synchronized and when you're in deep sleep it's hard to wake you up.”

Finally, during REM sleep is when you dream. Brain activity looks a lot like waking activity, and you see the eyes dart around quite frantically, but the rest of the body is in paralysis so you don’t move around. Harvey says that this stage is thought to be important for emotion regulation, and emotional functioning.

“Across the night you get this pattern of stage one and stage two, and then deep, and then back in to stage two sleep,” Epsie says. Dreaming sleep comes in cycles every 60 to 70 minutes across the whole night, and then you get more dreaming sleep towards the morning.

“That's the kind of broad architecture of your sleep across the night,” Epsie says. “A mixture of stage two sleep and dreaming sleep with most of your deep sleep at the beginning of the night. And you only every get about 25 percent of your night in deep sleep. That's normal.”

One myth about sleep, Wyatt says, is that a sleeping brain is an inactive brain—and that’s definitely not true. There’s a lot going on, and one of the most crucial things your brain is doing while you’re asleep is memory processing.

Almost all kinds of memory have been shown to be related to sleep in some way, Mander says. Your brain, while asleep, is reviewing and processing a lot of information that you learned today, whether it's factual information or you were learning how to do a new motor activity, such as learning how to bowl or how to play tennis.

There’s two kinds of brain waves that seem to be the most involved. One is the slow waves from deep sleep. “They're called that because of these lazy brain waves that are really tall and really slow,” Mander says. It takes between ¼ of a second to two or three seconds to complete one of these brain waves. That might not seem very slow, but normally, your brain is firing at speeds of 20 to 300 times a second. “That's a lot faster than oscillation taking two to three seconds,” he says.

The slow waves are also synchronous, where as usually the brain is firing at different times and all different places. The slow waves fire together, and then are silent together, and seem to be really important for memory.

The other kind of brain wave that is important for memory are the sleep spindles, They're that faster burst of activity, and sometimes they work together with slow waves to help knowledge that you learned be cemented in your brain long term.

And Mander says it’s more than just correlative studies that prove that these different sleep stages and waves lead to memory formation. There has been research where the expression of these brain oscillations has been manipulated, meaning the amplitude of the waves has been stimulated, or slow waves have been manipulated to pair up with sleep spindles—and it improves different kinds of memory.

It’s important to touch on each stage during a night of sleep, and Harvey says that studies have asked whether sleeping 8 hours, but broken up in smaller time blocks, could be sufficient. The answer was no, it’s not. “That will eventually lead to quite a lot of exhaustion, fatigue, cognitive decline," Harvey says. "We don't really understand fully yet why we need to go through all these stages, and why do we need to do it in the order that we do, but we know if it's defective, you're not getting as good quality sleep, and you feel that the next day."

No expert wanted to throw sleeping pills under the bus, because they could have a legitimate place in a carefully structured treatment plan for insomnia. But they also all agreed on something else.

All those different kinds of brain waves and sleep stages that natural sleep has? When you take a sleeping pill, you don’t get that. “Sleeping pills are sedation, not sleep,” Harvey says. They don’t produce natural sleep rhythms, and when you look at an EEG, the brain wave activity is very different from natural sleep.

“The ideal would be to have normal sleep structure,” Wyatt says. A lot of the prescription sleeping pills actually suppress deep sleep. You might be getting a little more sleep, but it's a poorer quality of sleep. It's a good trade for some people, and for others they may actually feel worse the next day from it.

“Right now there's no perfect silver bullet pill that makes your sleep into a perfect sleeper," Mander says. "And that's just the practical reality. There may be some that keep you asleep. There may be some that increase the certain amount of time you spend in certain sleep stages, but overall, the EEG just doesn't look the same.”

Credit: Lia Kantrowitz

Alcohol has a similar effect as a sleeping pill, in that it doesn’t let you get the same quality of sleep. “A lot of people will drink alcohol because they know it helps them to sleep,” Harvey says. But it's not sleep, it's also sedation, and what you end up doing is ruining your REM sleep.

Harvey says you’ll end up waking up more, even if you don’t remember, and won’t get the same length of sleep. “It affects both the quality and the architecture,” he tells me. “Although it feels sedating, in the long run, it's not really that helpful.”

Don’t let the word “natural” confuse you into thinking a product is better or more efficacious. Melatonin is an important circadian hormone; it’s called the "dark hormone" because your body secretes it as it gets darker because light suppresses its expression.

It could have a mild sleep promoting effect in the short term, but mostly what it does biologically is regulate your rhythms, Mander says. And you have to take it carefully at just the right times for it to work, so it’s best to coordinate with a sleep doctor.

“It's an oscillation, right?" Mander says. "It goes from low to high. So you don't want to keep melatonin high all the time. You want it to be high at specific times. And those specific times might not be right before you go to bed."

Wyatt helped conduct a study on melatonin, published in 2006, where 36 healthy young adult sleepers came to a lab for 27 days in a row and were put in isolation suites to get them on strange sleep schedules simulating shift work, jet lag, and insomnia. The researchers found that melatonin could be a very effective sleeping pill, but only when it was given to help people sleep during the daytime.

For an average sleeper, if you work during the day and you’re sleeping at night, your circadian system will have your brain release melatonin around two hours before you’re going to bed, so you’ll have high melatonin levels already. It stays high all night long and gets shut off around the time you wake up in the morning and then it clears away very quickly so that there are negligible levels present during the daytime.

Melatonin isn’t something you can take higher and higher of doses of to reach a greater effect, Wyatt tells me. Most drugs have what’s called a dose response function: You take a bigger dose, you get a bigger effect. “Melatonin seems to be more of an all or nothing function in the brain,” he says. For somebody who sleeps at night and has insomnia, taking melatonin won't help because your brain's already producing all it can handle."

Back to their findings: They found melatonin is really helpful is for daytime sleep. If you work at night and are trying to sleep during the day, or you’re jet lagged and trying to sleep at a time when the circadian system thinks it’s daytime, melatonin can help blunt that daytime alerting signal from the clock and help you sleep.

An across the board opinion from our experts: Your wearable fitness device is almost surely not an astute measure of your sleep, at least in the detail that it claims it can provide. “Some of these devices will dramatically overestimate the number of awakenings," Wyatt says. "They'll over or underestimate the amount of sleep. They're not terribly accurate."

Harvey says that the only way you could track the different stages of sleep is by looking at brain activity, so you would need electrodes on your head. Wearables use proxies like temperature or heart rate, which aren’t well validated. He says it can probably tell if you’re awake or you’re asleep, but they can’t track deep and light sleep, like they say they can.

Wyatt says that during his graduate work, he studied what happens to your memory as you fall asleep. Most people are nearly amnestic; they can’t remember anything for the minutes before they fall asleep. Part of the reason is that the brain is decreasing its arousal and not paying attention to its surroundings. Its memory systems are changing gears from processing current information to going back and reprocessing information it learned that day

Wyatt tells me they found that some people did not seem to have amnesia leading up to falling asleep, and that they could see a specific brainwave signature in these people. “It was almost a brainwave pattern typically just seen in wakefulness that was riding on top of sleep brainwaves,” he says.

Now this is called sleep state misperception, or paradoxical insomnia, and it's a common problem in insomnia. A lot of insomnia patients are actually sleeping, Harvey tells. They’ll tell you they’re sleeping three hours, when they're sleeping maybe five (still not great, though). Previously, this could be a source of contention for sleep doctors and their patients, but it’s now thought that people with insomnia don’t effectively cut out the outside world. Even though they're asleep, they're still processing the external world, which gives the subjective feeling of wakefulness.

“The thing about subjective-objective discrepancy: It's not there to tell us that people with insomnia are exaggerating things,” Epsie says. “People who have got insomnia have actually got more wakeful sleep. They're more alert during their sleep."

There’s thoughts that your brain is having during the night, but we're just not supposed to remember them, Wyatt says. “There are some people that keep the tape recording going, if you will,” he says. “And in the morning, they remember that track record of those thoughts and they assume, "Well that must've been that I was awake", when functionally most of their brain probably was asleep.”

It might also mean that our ideas of sleeping and waking need to be more nuanced. Wyatt tells me about a study from Yale in the 80s, where researchers woke people up at all different times during the night and asked them if they were awake or asleep. If people had been awake, they were 100 percent accurate knowing they had been awake. If they woke them up out of REM sleep or dreaming sleep, they were 93 percent accurate in knowing that they'd been asleep because most of them were dreaming and thought, "Oh I was dreaming, I must've been asleep."

But if they got woken up out of stage two sleep, which is a medium depth of sleep, their accuracy fell to almost 50 percent. Half the time when woken up out of sleep they were wrong and thought they'd been awake. When researchers woke them up out of stage four sleep, which is the deepest sleep of the night, the participants were only right 35 percent of the time, meaning that most of the time, they got woken up out of the deepest sleep and thought they had been awake.

“People who have got insomnia are more likely to be asleep and awake at the same time,” Epsie says. “In other words, this idea of being asleep or awake being two different, completely different, classes of behavior, is not entirely true. People can be in various stages of sleep or sleepiness during their waking day and during their sleeping night can be in various stages of wakefulness. If you think of somebody, for example, who is sleepwalking. Sleepwalkers are clearly asleep and awake at the same time.“

The recommended treatment for insomnia is cognitive behavioral therapy for insomnia, or CBT-I. CBT can help tackle thoughts and behaviors that cause or make sleep problems worse, Epsie says. And you retain the normal structure of the sleep (since there's no sedation involved).

And even though therapy is not a pill, there are connections between the behavioral changes people make in CBT and physiology in the brain. One example that Wyatt give me is called “sleep restriction” or “sleep compression.” He’ll extend the length of someone’s day to make them a little bit sleepier when they’re trying to fall asleep.

The longer you’re awake, a chemical called adenosine is building up in your brain, which is a waste product of other cells in the brain doing work. Adenosine is a sleep promoting substance, Wyatt says. So if you keep someone up longer, they could have more adenosine and fall asleep faster. “That's a behavior change, just having them change how long they're in bed, but it's directly impacting fundamental biology in the brain.” Wyatt says.

Another intervention is called sleep scheduling, where he’ll advise a person with a chaotic sleep schedules to keep a consistent bedtime and wake up time for a couple of weeks. “That will, within a couple of days, line somebody's circadian system up to that desired sleep/wake schedule," Wyatt says. "Again, we're just changing a behavior, but it directly impacts the circadian biology in the brain.”

CBT also recommends people to control or moderate alcohol and caffeine, along with the timing of exercise. Lastly, Wyatt tells me that the cognitive interventions are crucial too. This might be helping a person get over lying in bed and ruminating over their to-do list or what happened that day, or obsessing about the fact that they’re not sleeping. “We're not trying to convince people that they're wrong in what they're thinking, but what we'll try to do is get them to have sleep-related thoughts or thoughts about their insomnia that aren't as extreme,” Wyatt says.

People can unburden their whole day when they go to bed at night, Epsie tells me. So he encourages people to “put the day to rest.” “That involves just sitting down in the early part of the evening and, literally, going through the day and planning the next day and putting the day to rest,” he says.

CBT can also help the people who are trying too hard to fall asleep, the “fixers,” as Epsie calls them. “They're often good at fixing stuff. Maybe other people go to them and they help people fix their problems too because they're very good at fixing stuff. But the thing about insomnia is if you try to fall asleep you're more likely to remain awake.” Espie says.

Wyatt says that it’s not great to look at your phone before bed, and he wouldn’t advocate for it, but the emphasis on that bit of advice might be over hyped. He says that the studies he’s seen on the effects on sleeps of screens are statistically significant, but the actual impact isn’t one he’s too concerned about, and might not be a huge difference in how long it takes you to fall asleep in minutes.

And if you really need to do some scrolling right before bed, there are other potentially more influential habits you could pick up. Mander says that if he were being forced to pick sleep hygiene habit, it would be to keep regular sleep habits. Go to bed and get up at the same time every day. You shouldn’t chronically restrict your sleep to make it happen, but try to make sure you’re on some kind of regular pattern. Harvey agrees that as much as possible, you should try to keep the same sleep pattern. “if you are a troubled sleeper, I think it is really important,” he says.

Harvey also says, if you’re lying in bed and you’re not sleeping and getting frustrated, you shouldn’t continue to languish in bed. “Get up and get out of bed, and go to a different room, and accept the fact that you're not sleeping, and do something kind of relaxing,” he says. Epsie suggested this as well. He calls it the quarter-of-an-hour rule. Good sleepers fall asleep within 10 to 15 minutes comfortably, he says, so if you’re past that it’s best to get up than lie there worrying about it.

Another easy and quick tip: get a red night light, not a green, blue or white one. He says the circadian system is really sensitive to green and blue light (both are present in white light). If you go to the bathroom in the middle of the night, and blast yourself with white light, it could start to shift your rhythms.

“If you want to really stabilize your sleep get a red night light," Mander says. "Your circadian system is blind to red light."

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