We’ve all heard that we should be getting seven to nine hours of sleep per night. It’s a maxim drilled into us when we are children. Most of us even had a bedtime and for some of us that bed time was strict!
Then we hit 18 and all the rules went out the window for a decade or two. But at some point — presumably after some reflection on how enjoyable life can be with a good night’s sleep, not to mention how unenjoyable it is without — we started to try to get “normal” amounts of sleep.
But here’s the thing. This whole time we’ve been focusing on amount of sleep. There’s a whole other variable that is sitting in the shadows that we haven’t talked about — at all!
Let’s talk about quality. Don’t worry, I’m not going to get all Zen and the Art of Motorcycle Maintenance on you, but the quality of this sleep is arguably just as important as quantity. We may be carving out eight hours to be in bed, but it doesn’t mean that we actually get restful, restorative sleep for those eight hours.
Let’s pull back the curtain, shall we?
Good sleep quality is essential for optimal well-being, wellness, and overall vitality. What does it mean to be getting high-quality sleep, and how does it compare to low-quality sleep?
It turns out that sleep quality is much more multidimensional than sleep duration alone. For this reason, even experts don’t fully agree on what constitutes good-quality sleep. Let’s look at some commonly accepted guidelines for how sleep quality is defined, how it is measured, what affects it, and how to improve it.
How is sleep quality defined?
Sleep quality is best understood as a combination of interacting factors, some subjective, some behavioral, and some physiological.
In 2016, the National Sleep Foundation assembled a panel of experts to answer the question, "what is good sleep quality?" After reviewing and discussing over 270 studies, the panel members agreed on several guidelines for what defines good-quality sleep in adults, namely:
- Sleep efficiency: Spending at least 85% of the time asleep while in bed
- Sleep onset latency: Falling asleep within 30 minutes or less
- Nocturnal awakenings: Waking up no more than once per night
- Wake after sleep onset: Drifting back to sleep within 20 minutes if one does wake up while sleeping.
Since these measurements are general guidelines, someone might find that a single factor may be more important to them than any of the others. For a person that has a problem falling asleep, sleep onset might be the strongest determinant of quality. Another person who frequently awakens in the middle of the night may find sleep onset is relatively trivial for their sleep quality, and so may just keep an eye on their week-to-week nocturnal awakenings.
The caveat to all of these components is that sleep quality is not a constant over a lifetime. Sleep tends to change as we age. For instance, newborns spend much more time in REM sleep, and so require more than the recommended time period for adults. The elderly spend less time in deep, slow-wave sleep and may still have good sleep quality even with 2 nocturnal awakenings per night. It’s important to note, however, that with age comes an increased risk of medical problems, which are often chronic. Generally speaking, people with poor health or chronic medical issues have more sleep problems, which could reflect some of the changes in sleep architecture experienced by the elderly.
How is sleep quality measured?
There are a bunch of ways to measure sleep. The trouble is that, outside of a sleep lab, accuracy can be limited, leaving us primarily with subjective options.
Objective sleep quality is measured in the lab with a sleep study called polysomnography. Polysomnography is an overnight study that records brain waves, oxygen levels in the blood, heart rate, breathing, and eye and leg movements. This data can be used to give a comprehensive assessment of the percentages and amount of time spent in each of the sleep stages (N1, N2, slow-wave sleep and REM sleep) we find ourselves in throughout the night.
Such studies can also tell us how long it took to fall asleep, the total sleep duration, the number of awakenings, and the amount of sleep disturbances such as sleep-disordered breathing and periodic limb movements. Since this is the gold-standard sleep measurement technique that gives the most complete picture of how well and when we sleep, it is commonly used to diagnosis sleep disorders.
Commercially-available sleep trackers estimate sleep quality indirectly with movement data in a process called actigraphy. The wearable trackers typically use an accelerometer to measure and analyze movements throughout the night.
Muscle movements can be used as a proxy for sleep staging (we’ll go through sleep staging below) with reasonable accuracy, as different phases of sleep have different movement-related markers. For instance, in healthy REM sleep, our muscles are paralyzed in order to prevent us from acting out our dreams, so these devices will register no movement during this time.
The limitations of these commercially available sleep trackers’ methods of measurement is that they can have difficulty distinguishing between being merely motionlessly awake and asleep, and so may overestimate sleep in some people.
While these devices commonly claim to measure sleep quality, they may be best used to measure total sleep time. Since they can be worn effortlessly over multiple days, they can characterize our sleep/wake rhythms with reasonable accuracy and give us insight into our sleep patterns.
Self-rated sleep quality
Self-rated sleep quality, also known as subjective sleep quality, refers to a self-rated estimation of how we slept. For instance, it can be based on our mood and energy levels the next morning, or by memories of frequently awakening throughout the night.
When we wake up from sleep we deem poor quality, we may feel groggy, inattentive, slowed down, or generally unrestored throughout the day. We may remember tossing and turning throughout the night or frequently waking up.
Although this is a fundamentally important component of assessing sleep quality, it can be difficult to accurately gauge one’s own sleep quality. Self-reports of sleep quality are limited by the fact that we lose consciousness during sleep, so we are naturally poor self-observers of how well we slept.
Self-reported sleep quality often does not correlate well with clinical markers of sleep quality, as measured by the sleep trackers used for sleep studies. As you might have suspected, we humans are terrible at self-reporting the quality of our sleep.
In the extreme, this is a hallmark of a condition called paradoxical insomnia, a variant of insomnia also known as sleep state misperception. Individuals with this condition report having heightened awareness of their sleep surroundings and spending hours awake during the night.
However, from the outside, they appear to be sleeping well, and have all of the characteristics of sleep in their sleep study analysis. Paradoxical insomniacs overestimate how long it takes to fall asleep and underestimate their total sleep time, despite only mild to moderate signs of daytime fatigue.
Apart from self-reports, understanding our sleep stages with sleep tracking devices can also give us varying degrees of insight into our sleep quality. These devices can give us a data-driven understanding of sleep architecture, which can inform our overall sleep quality.
Sleep is classified within two main stages: non-REM sleep and REM (Rapid Eye Movement) sleep. Non-REM sleep proceeds in three stages, the last of which is deep, slow-wave sleep or delta sleep. After cycling through non-REM, we enter REM sleep, and the cycle then repeats again roughly every 90 to 120 minutes, with increasing amounts of REM and decreasing amounts of slow-wave sleep.
Poor sleep quality is commonly associated with disruptions between the transitions of these sleep stages.
It’s worth noting that the sensors used by consumer devices are not directly measuring key variables like brainwave frequency to project how you move between sleep cycles. Instead, they use accelerometers and in some cases heart rate. They also use proprietary algorithms that are not available for public scrutiny. In short, the accuracy of commercially available sleep trackers can be a bit questionable. You can learn more about sleep trackers here.
Pittsburgh sleep quality index
If you’re trying to figure out where you stack up sleep quality-wise, a good place to start is with the Pittsburgh sleep quality index (PSQI). The PSQI is a self-administered questionnaire developed in the late 1980s that is commonly used to clinically assess sleep quality and disturbances over a period of one month.
The index is made up of seven components that are rated in terms of severity to distinguish between good sleepers and poor sleepers. This includes:
- Subjective sleep quality
- Sleep latency
- Sleep duration
- Habitual sleep efficiency
- Sleep disturbances: Includes nocturnal awakenings, using the bathroom at night, coughing, snoring, pain, nightmares, and feeling too hot or too cold.
- Use of sleep medication
- Daytime dysfunction: Includes problems staying awake while driving, eating meals, engaging in social activity, and general loss of productivity.
The scores from each component are summed to create a global sleep quality score. A score greater than five indicates poor quality sleep with a diagnostic sensitivity of over 89%. Here is a copy of the PSQI that can let you easily rate your sleep quality at home.
What is quality sleep by the numbers?
We’ve gone through REM and NREM and now might be wondering how much of your night you want to be spending in each of these. Most healthy adults will spend about 16-20% of their total sleep in slow wave sleep, and 21-31% of their total time asleep in REM. The remaining is primarily spent in the N2, the second phase of NREM.
According to Dr. Robert Stickgold, Professor of Psychiatry and Direct of Center for Sleep and Cognition at Harvard Medical School, periods of REM sleep get longer and stronger as the night progresses.
“We want lots of REM late in the night, we want lots of slow-wave sleep early in the night, and we want a rhythmic REM cycle,” Dr. Stickgold said.
What is known to affect sleep quality?
Here are five of the most common things that result in poor quality sleep. Some of these are sleep problems that may require medical intervention to help, but many can be eliminated by incorporating better sleep hygiene into your life.
A wide range of sleep disorders impacts sleep quality either during sleep or in the transition to sleep. Insomnia affects sleep quality the most directly, since it is diagnosed based on an inability to fall or stay asleep. Insomnia affects one in 10 Americans chronically and is associated with non-restorative sleep, daytime fatigue, and problems with mood and concentration.
Obstructive sleep apnea is one of the most prevalent sleep disorders that causes temporary obstructions of breathing during sleep. The sleep interruptions can result in sleepiness, daytime fatigue and in severe cases, medical issues such as heart problems.
Restless Legs Syndrome (RLS) impacts sleep quality by creating irresistible urges to move the legs. Since RLS makes it difficult to fall into a restful sleep, it can result in exhaustion, daytime sleepiness, and problems with mood, concentration, and job or school performance.
Stimulants act on the central nervous system to increase mental alertness, energy, and attentiveness, thereby reducing feelings of sleepiness.
When stimulants such as caffeine or nicotine are used five or fewer hours before bedtime, they can cause problems falling asleep or disrupt the quality of sleep. Learn more.
Napping can be useful to reduce fatigue and improve mood, but it shouldn't be used as a regular substitute for poor quality sleep. Taking frequent, long naps (longer than 100 minutes) is associated with poor quality sleep.
Long and frequent naps can disrupt our circadian rhythm and interfere with nighttime sleep. Limit daytime naps to ten to twenty minutes to not disturb sleep cycles later when we fall asleep at night.
The position we sleep in can dramatically affect sleep quality. Since one person’s sleeping position may not be the best for someone else, it’s always best to tailor your sleep position to your unique sleep needs.
The fetal position is the most common sleep position. It can be helpful for lower back pain, pregnancy, and to reduce snoring. This position is best if it is not too tight, otherwise, it can interfere with deep breathing and cause joint stiffness.
Although this isn’t a common position, sleeping flat on your back can help prevent acid reflux and lets your spine rest in neutral alignment. It may make snoring worse though, which can disturb sleep. Individuals with sleep apnea should avoid sleeping on their back.
Sleeping on the side can be beneficial since your spine is able to rest in its natural alignment. It allows you to breathe easier and can reduce heartburn. The downside is it may cause wrinkles on one side of the face.
Sleeping on your stomach may reduce snoring, but it can put pressure on the spine and cause lower back and neck pain. Pregnant people should avoid sleeping on their stomach. If you sleep on your stomach, it can help to put a pillow under your pelvis to restore the back to a more neutral position.
Eating too close to bedtime
Eating and drinking right before bedtime can cause heartburn, digestive issues, and the need to use the bathroom in the middle of the night.
Instead, eating a light, healthy snack a few hours before bed can be beneficial. It can stabilize morning blood sugar and prevent you from waking up hungry during the night.
Mood and psychological state
Sleep can be disturbed by mood and psychological state. Stress and anxiety are well-known to cause sleep disturbances, including prolonged sleep latency and multiple awakenings during the night.
Depression is characterized by alterations in sleep quality, including early morning awakenings, decreased deep sleep, early onset of REM sleep, and in some cases, longer REM sleep duration.
We’re increasingly learning that sleep plays a fundamental role in emotional regulation. Recent research has shed light on how sleep, especially REM sleep, is a key player in processing the emotional “tags” on memories. If there is an overload of emotional information to be processed (as seen in mood disorders like depression and PTSD), this may cause sleep disruptions, which can further reduce emotional processing by shortchanging us of restorative sleep in a vicious cycle.
According to Dr. Robert Stickgold, “We have more and more things that are both emotional and not completely processed that fall into that category of what sleep will tag and try to deal with one way or another. As we get more and more things tagged that way, we reach the limit of the system's capacity.”
Dr. Stickgold continues, “And I suspect that, when that happens and you get through the end of the night and you can feel that there's still unprocessed material that your brain had wanted to process, you wake up and you feel exhausted. You feel like you were working all night.”
How to improve sleep quality
You’re probably thinking: “Finally! Now I can learn the secret to improving sleep quality.”
The first thing to know when making changes to your sleep is that performance is a slow process. It’s like navigating a shipping vessel; it takes time to alter your course.
But, sticking to these helpful sleep habits can increase the quality of your sleep and make you feel more refreshed as you ease into a sleep-promoting routine.
Turn off the electronic devices one hour before bed.
The blue light emitted from these devices can disturb restful sleep. If we are inundated by the light from these devices at night, our brains will still think it is daytime and won’t produce the hormones that are needed to make us feel naturally sleepy.
Adjust the thermostat in your room to 60-67 degrees Fahrenheit.
In addition to light, temperature is a strong signal for our body to initiate sleep. Our body’s core temperature naturally drops before we enter a sleep cycle, so keeping the room cool can help us fall into a more restful sleep.
Make sure your room is quiet, comfortable, and dark.
Tailoring your bedroom to be quiet, comfortable and dark can be very beneficial for high-quality sleep. Try using blackout curtains, comfortable bedding, and eliminate sources of light from chargers or other LEDs. It is also good sleep hygiene to only use the bed for sleeping, which reinforces the connection between the bed and sleepiness.
Quality sleep is the sum of multiple physical, emotional and environmental factors. To make a meaningful change, it’s important to look at the big picture. In most cases, improvements won’t come from one change to your sleep hygiene or sleep routine, rather it will be the outcome of multiple shifts over time.
There are multiple ways to get there. You can take a biohackers approach to improving your sleep, experimenting with different approaches and measuring your success.
Alternatively, you can talk to a sleep coach who can help you come up with a personalized strategy.
Natural supplementation along with meditation and proper sleep hygiene are a good start for those wanting to test the waters. In traditional Chinese medicine, natural supplementation is one of the pillars of health. Learn more.
Polysomnogram: A sleep study used to diagnosis sleep disorders. Records brain waves, heart rate, breathing rate, oxygen levels, and eye and leg movements in an overnight assessment.
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