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We spend around a third of our lives asleep, and most of us put effort into getting the best sleep we can. Apart from looking for the right bedding and nighttime environment, a great technique to improve sleep is to use a wearable sleep tracker. We obviously can’t know what we’re doing when sleeping, so wearing a sleep tracker on the wrist or finger can provide information on physical activity during sleep, which can be a good indicator of sleep quality. Bad sleep quality is usually an indicator that reading our post on improving sleep hygiene is a good idea.

This month Molekule is partnering with Oura Ring to spread the word on sleep trackers and how much they can help sleep hygiene. There has been a lot of research on sleep trackers recently, and so far it seems like they aren’t quite as good as clinical research equipment in a sleep laboratory. But the findings are indicating that using a sleep tracker can help to gauge different aspects of sleep quality and even assist in deciding on the best steps to improve sleep hygiene or if medical treatments are working.

How to measure sleep quality

There are three basic types of sleep as defined by brain activity: light sleep, deep sleep, and REM sleep. These mental states need to be activated by brain chemicals such as GABA in the right order, duration, and quality for the most recharging sleep. By measuring when these start and stop, sleep doctors can identify if your brain’s sleep rhythm is off and how it might be reset with nighttime or daytime treatments.

The gold standard of sleep quality measurement is known as polysomnography or PSG, which is similar to an EEG or EKG that you might receive for neurological or cardiac diagnoses. PSG is very effective in detecting changes in sleep patterns but requires very specialized equipment that is only available in a sleep lab. It requires 20 or more leads to be stuck on the head, face, and body to measure metrics like heart rate, brain waves, blood pressure, oxygen levels, and movements of the body or eyes.

Man getting polysomnography leads attached to his arm

None of us want to spend tens of thousands of dollars on PSG equipment and get a degree in sleep research, so it isn’t practical to use at home. Over the past five or so years, a lot of research has been done to correlate wearable sleep devices with PSG data and see how well they match up. It’s been found that while wearable devices can’t quite match the accuracy of attaching leads to the skin, they are still quite useful in finding out if your sleep quality is good.

What is good sleep?

Good sleep involves enough continuous hours at the right time of day and night. Without a sleep tracker it’s simple to know how long you were in bed, but maybe not how good your sleep was.

There are five defined stages of the sleep cycle: awake, light sleep, deep sleep, slow wave sleep (also known as deepest non-REM sleep), and REM sleep.

Light sleep is only 5% of our total sleep time and usually lasts 1 to 5 minutes. It is usually just the first few minutes after laying down as we relax or between sleep cycles.

Deep sleep increases throughout the night from 10 minutes to 60 minutes per cycle. It’s associated with slower brain waves but an active brain that is organizing memories. Deep sleep is when teeth grinding may occur.

Slow wave sleep is typically 20 to 40 minutes and is when our body is repairing itself rather than our mind processing the day. It’s very difficult to wake from and tends to cause “sleep inertia” or a slow and foggy mind for up to 30 minutes if interrupted.

REM sleep also takes more of each sleep cycle as the night progresses and is anywhere from 1 to 60 minutes. During REM breath and eye movement may become erratic and the brain may use up to 20% more calories.

Illustration of woman sleeping with sleep stages in a pie chart form

A sleep cycle typically lasts 90 to 110 minutes and repeats multiple times throughout the night. Deep sleep and REM sleep increase as morning comes, with the final cycle sometimes having a full hour of REM.

Good sleep is long enough

We all have slightly different sleep needs, but The National Sleep Foundation recommends 7 to 9 hours of sleep for adults or 4 to 6 sleep cycles. The developing brains of children require more sleep, and newborns may require up to 17 hours while teenagers might need 10 hours. Genetics is a huge factor in sleep needs, and one study found that some family groups can sleep 4 to 6 hours a night and not suffer any negative health consequences.

Good sleep is continuous

Waking up or otherwise having sleep disrupted during the night is just as bad as not sleeping enough hours. Sleep apnea is one of the most common disruptions to sleep continuity. It affects more than a billion people worldwide and considerably more men than women. In addition to the brain fog of being sleepy, sleep apnea can also cause heart problems, liver disease, diabetes, and other complications.

Good sleep happens at the right time

We all have circadian rhythms, which are predetermined systems in our bodies that make us function best when awake during the day and asleep at night. The amount and angle of light we see after the natural light of the sun has set can disturb this rhythm. Going to sleep at times other than the end of the day or having an inconsistent sleep schedule can cause health problems.

Good sleep is also satisfying

Sleep satisfaction isn’t measured with polysomnography, but can be an important part of well-being because not getting enough sleep is one of the main reasons someone doesn’t feel healthy. Anxiety and depression are both linked to poor sleep quality, though anxiety is more associated with daytime sleepiness.

Man trying to sleep at night but awake at close 3 o'clock in the morning

What is bad sleep?

One study on Medicare recipients found that bad sleep has such a negative impact on health it increased the need for all types of healthcare. Bad sleep or insomnia is often best defined by the person suffering from it, but The Sleep Foundation also provides a few numbers. If any of the following are regularly true, your sleep quality may be lacking:

  • You wake up more than once during the night or are awake for more than 20 minutes when you do
  • It takes you more than 30 mins to fall asleep
  • You spend less than 85% of our time in bed asleep

It can be hard to figure out if these problems are happening consistently enough for sleep quality to be an issue. A sleep tracker can gather some information about the above so you and your doctor can have a better idea of how well you are sleeping.

Sleep trackers work

Wearable sleep tracking devices aren’t polysomnography machines so can only pick up a handful of your body’s metrics, like heart rate, blood oxygen, and movement, but the small-scale research coming out so far indicates they may improve sleep quality. However, for minimum usefulness a sleep tracker needs to be directly compared to the instruments used in a sleep research lab.

A sleep tracking app open on a smartphone next to a sleeping woman in a bed

Our friends at Oura Ring have done extensive research comparing their tracker against PSG, and other makers of wearable sleep trackers have done a lot similar research. This is important because very few of us are equipped to properly interpret sleep quality information, so also a device with an app that features detailed visualizations and graphs of sleep data will help to communicate suggestions and summaries.

As with any new technology and the science around it, there are a few caveats to keep in mind when using a sleep tracker. Here are a few points on what you should expect from a sleep tracker.

What sleep trackers do well

  • Sleep trackers are reliable for overall trends. While perfectly detecting every brain wave is out of reach, sleep trackers will empower you with new information about your behavior at night.
  • Sleep trackers are great for measuring sleep duration. One study found that sleep trackers were able to tell the difference between sleep and wakefulness 78% of the time, and were able to pinpoint the exact moment when sleep starts 38% of the time. Another study found that sleep trackers also did well identifying sleep duration, but could not differentiate between sleep stages well. This varies between devices and the Oura Ring, for example, is accurate about 82% of the time.
  • Sleep trackers are ideal for recording your sleep quality progress. By being connected to a smartphone or computer, a sleep tracker will create a lot of data. Good sleep tracking apps also include tips and goals along the way. Ways to track daytime activity, caffeine or alcohol intake, bedroom environment, and other bits of data can really help to show where sleep hygiene can be improved.

Drawbacks of sleep trackers

  • Don’t think about sleep quality while trying to go to sleep. It might be wonderful to have more insight into your sleep, but some studies have been finding that becoming preoccupied with sleep quality can have a negative impact by causing stress or worry. If you find yourself thinking about sleep tracking instead of actually sleeping, it might be a good idea to try a different solution.
  • Don’t let poor quality sleep keep you down. Along the same lines, a study where participants were given fake sleep scores from their wearable devices showed that just the perception of a good or bad night’s sleep can affect mood and fatigue regardless of how well they slept. The study was from 2018 when sleep trackers were less accurate and an incorrect reading was more possible, so it’s best to use a sleep tracker that has recent technology and research to show its accuracy.
  • Sleep tracking data is best used by you. While it is definitely a good idea to talk to your doctor about any sleep problems you have, one small study found that patients are much more likely to engage with sleep tracker data than their doctors, who can’t rely on it for diagnosis. The data you gather is most useful in telling you if your sleep is improving as you improve your sleep hygiene.
  • Interpret sleep stages with caution. Wearable sleep trackers don’t detect brain waves yet, so they can’t directly detect if you are in light, deep, or REM sleep. Different trackers have different software that will have varying degrees of effectiveness, so be sure to do your research. The sleep experts at Oura Ring use the high sampling rate and accurate sensors to measure sleep stages accurately about 65% of the time. Sleep experts have an inter-score variability of 82% when interpreting PSG results.

In summary, most of us will learn more about our sleep by using a sleep tracker. The most useful sleep trackers extend sleep hygiene management across the whole day, and can record possible environmental and lifestyle factors that influence sleep. Those of us suffering from poor sleep quality can use a sleep tracker to track treatments and goals, but won’t be able to narrow down specific sleep issues with only a tracker. As time goes on, this technology will continue to improve our control over our sleep and could match the tools used by the scientists soon.


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