Your wearable is lying to you about sleep
What you should do about it
Bad sleep kills
Sleep is the most important element for your health, arguably more important than nutrition or exercise. There are over 260,000 scientific studies on sleep on PubMed. What they find is simple: disrupted sleep kills you, makes you unhappy and unproductive. Everything is worse from bad sleep.
The average person lives 10 years less due to bad sleep.*
Good sleep is not just sleep duration, although the volume itself is a huge problem. Good sleep is also about proper sleep architecture. This is a fancy way of saying you need to have good quality for each of the sleep stages: stage 1, 2, and especially deep sleep and REM sleep.
How much deep sleep did you get last night? What about REM sleep?
If you have a wearable, such as an Apple Watch, a fitness band, an Oura ring or a sport watch, you will be looking at it now. It will tell you that you got X minutes of deep sleep and Y minutes of REM sleep.
Your wearable is lying to you.
It cannot measure your sleep stages.
Although companies make big claims about sleep stages, they don’t offer any actual proof that their product are tracking these. However, there have been scientific studies evaluating their accuracy on sleep.
This study found the Oura ring had an agreement of 51%-65% in detecting the sleep stage. So it was right in identifying the sleep stage about half the time. That is as good as if you were to throw a coin to guess which sleep stage you were in.
It’s not just Oura. All current wearable have similar or worse precision for measuring sleep stages, as seen in all the studies that evaluate this: 1, 2, 3, 4, 5, 6, 7, 8, 9.
As one study author puts it: “High variability in sleep stage-tracking performance suggests that these devices, in their current form, are still best utilized for tracking sleep-wake outcomes and not sleep stages.”
If you don’t have the patience to read scientific studies, there is also a scientist on YouTube (Quantified Scientist) who tests wearables versus professional gear. One thing he does is compare the sleep measurement, including of sleep stages, versus polysomnography. It’s really good, of course with the caveats that it’s still experiments with N = 1.
Should you ditch your wearable?
No!
They are bad at estimating sleep stages, but they are adequate for measuring total sleep duration and awake time. This makes them great tools to monitor your overall sleep. You should look at valuable indicators like: total sleep time, amount and duration of time awake during the night and HRV during the night.
Sleep duration alone makes your wearable worth its price. Studies show that measuring sleep duration leads to better and longer sleep.
It’s simple. If you don’t measure it, you don’t really have a good sense that it might be bad. And you cannot look back and see when it was bad, and thus deduce what harms your sleep. Without sleep tracking, we have to rely on subjective perception and memory. As overwhelmed with information as we are now, it’s easy to not notice you are sleeping too little.
When you add the other data on top, it’s even more valuable. Are you having awake moments in the night? Are they long? What is happening then? They are signals of a potential issue like chronic anxiety, urinary issues (if you get up to pee many times), or sleep apnea. The same with HRV during the night.
Ignore sleep stage data. It’s false.
The only thing you should change is to ignore the sleep stage data on your device. Don’t look at deep sleep. Don’t look at REM sleep. Don’t look at light sleep. Look at total sleep time. That’s all.
The ideal life is easy when you know what you need,
Victor
*Note: soon I will release a calculator to determine how many years of life, productivity and happiness you can gain by optimizing your sleep. It’s based on the existing scientific research. Stay tuned for more soon.