The Oura ring is a novel, multisensor device that claims to be able to distinguish sleep stages, including REM sleep. I purchased one recently and after several months of evaluation and an extensive look at the data supporting it I have to say I am much more impressed with Oura’s hype, marketing, and style than any useful or actionable information about sleep that comes from it.
The Oura website is full of pictures of cool people doing cool things wearing their Oura rings — like this guy.
It’s also chock full of marketing blather that implies that somehow the ring will dramatically improve your sleep and your waking life.
“We see every individual as unique: your state of health and wellness today, tomorrow, and days to follow. Getting enough restorative sleep has a profound impact on mental and physical health and performance. Your daily choices and rhythms define how well you sleep. With Oura, you learn your optimal times to move, eat and take a break to get that restorative sleep.”
“Giving you actionable steps to improve your life opens a totally new universe of possibilities – be it for mental, cognitive or physical performance, or for beauty, health, and longevity.”
A quick look at the Oura web site certainly conveys the sense that this is the slickest, most cutting-edge personal wearable sleep and activity tracker one could purchase.
However, despite Oura’s tantalizing claims, there is only one legitimate scientific comparison of the ring to the gold-standard of sleep evaluation, polysomnography (PSG). This was published by SRI International researchers in 2017 in Behavior Sleep Medicine. Its full contents can be read here.
In addition, there is no published evidence whatsoever that changing one’s behavior based on the various parameters that the ring produces will have any favorable effect on your sleep quality or health in general. I’ll be quoting from that 2017 published paper, which I think is a good, unbiased analysis, and I’ll throw in some of my own observations throughout this piece.
How It Works and What It Claims To Do
A good night’s sleep — everyone should know by now — is incredibly important to optimal performance the next day. In addition, poor sleep quality is linked to a whole host of pathologies (with causality yet to be proven for most.) Thus, I quickly purchased an Oura ring after hearing cancer surgeon-turned-“longevity”-doctor Peter Attia rave about his.
Oura likes to promote the idea that it has some sort of special way of measuring sleep based on a combination of sensors.
The Finnish company claims to use these physiological signals (a combination of motion, heart rate, heart rate variability, and pulse wave variability amplitude) in combination with sophisticated machine learning-based methods to calculate deep (PSG N3), light (PSG N1+N2), and rapid-eye-movement (REM) sleep in addition to sleep/wake states.
After obtaining a sizing kit from Oura, I selected my ring and within a few weeks it was delivered. I downloaded the free iPhone app, charged the ring with the supplied USB charger, slipped it on my left ring finger and eagerly awaited my first night’s analysis.
Upon arising in the morning, I opened the Oura app and visualized an entrancing display like the one below.
It’s a nice graphic summary of the night’s sleep with my minutes of REM, light, and deep sleep nicely quantified.
More graphs and more data are available by connecting to Oura’s online application which automatically syncs to your smartphone app.
Unfortunately, the app was telling me that I was awake for 109 minutes of the time I was in bed. Which was not correct. I was truly awake only for 10 minutes around 1:30 a.m. This overestimation of my awake time has been a consistent error of the ring for my recordings. If the app can’t accurately track awake time, all of its metrics are going to be inaccurate.
In fact, over several months of using the ring and app, I have found little relationship between how I feel after sleeping versus how Oura has rated my sleep. There is even less correlation between the “readiness” score that Oura produces and how I feel during the day. Overall, I have found absolutely no actionable information from my months of using the ring.
One morning, Oura gave me a “readiness” score of 68 and told me: “Don’t push it. Your resting heart rate was above average, so you might not be fully recovered.” I felt great throughout the day. These recommendations in my experience are almost universally inaccurate and useless.
Oura also makes recommendations on when it thinks you should go to bed. One time it told me I should go to bed at 7 p.m. I have been ignoring its advice in this area.
Now, I am just one individual. It is entirely possible there is something unique about my sleep that invalidates the ring’s accuracy. The ex-eternal fiancee tells me I’m a restless sleeper.
In fact, devices that rely on actigraphy tend to be fairly accurate at identifying when you are sleeping but not when you are awake, which is the opposite of what Oura is doing in my case.
The SRI paper put it this way:
“Compared to PSG, actigraphy has high sensitivity (ability to detect sleep) although specificity (ability to detect wakefulness) is lower (Marino et al., 2013; Sadeh, 2011), with a wide range of accuracy, depending on the amount of night-time wakefulness (Paquet, Kawinska, & Carrier, 2007), the algorithms used and the particular population studied (Van de Water, Holmes, & Hurley, 2011). Most importantly, actigraphy relies on a single sensor, an accelerometer, and thus it provides a measure of motion from which it predicts sleep and wake states. However, information about sleep stage composition, fundamental in studying sleep and sleep disorders, is not provided.”
Science Behind the Analytics: Detecting Sleep Stages
So what does the SRI paper Oura likes to quote as proving its accuracy say?
The paper is entitled “The Sleep of the Ring: Comparison of the ŌURA Sleep Tracker Against Polysomnography,” and it was written by researchers at SRI International, a research consortium in Menlo Park, California, with no ties to the company.
Another paper that used to be touted on the Oura Ring website (but is no longer referenced on the site) utilized home PSG recordings and was done by an Oura employee.
The SRI researchers studied 41 healthy adolescents and young adults (average age 17). Sleep data were recorded using the Oura ring and standard PSG on a single laboratory overnight. Metrics were compared using Bland-Altman plots and epoch-by-epoch analysis.
The ring accurately detected “light” and “deep” sleep in 65% and 51% of the sleep epochs, respectively. It also accurately detected 61% of REM sleep epochs, with an overall overestimation of PSG REM sleep (by about 17 min). When the ring misclassified PSG REM sleep, the algorithm usually classified the epoch as “light sleep” (76%).
These data suggest that the Oura Ring is virtually useless in telling you if you are in REM sleep versus deep or light sleep.
As the authors noted, “Distinguishing sleep stages such as REM and N3 with non-EEG based systems has been challenging and is a goal of several commercial sleep-trackers, with mixed success.”
“Clearly, further work is needed to determine what combination of sensors might be used to optimally develop an algorithm that differentiates sleep stages sufficiently well to detect real differences or changes in healthy and clinical populations.”
A look at the Bland-Altman plots’ shows that some individuals had considerable over-estimation of REM time whereas others had considerable overestimation of REM time.
Although Oura REM time was on average only 17 minutes higher than the PSG REM time, this was because the marked overestimation of REM time in some (over 30 minutes in seven subjects) was balanced by marked underestimation in others (nine subjects with over 40 minutes and one with 160 minutes).
Given that the average REM time was 92 minutes for most subjects, there was a significant discrepancy between PSG and Oura assessments.
Coin Flip For Detecting Awake Time
Oura ring was also pretty useless at identifying when you are awake.
Overall, Oura had 96% sensitivity for detecting sleep, 48% specificity for detecting wakefulness, 65% agreement in detecting “light sleep”, 51% agreement in detecting “deep sleep”, and 61% agreement in detecting REM sleep, relative to PSG.
Like other sleep sensors utilizing actigraphy, Oura in most individuals can’t accurately differentiate between times when you are lying still but awake and when you are lying still and asleep.
The limitations of wrist actigraphy for differentiating sleep from wake are worse in those with insomnia, as “subjects who are awake but lie motionless can be classified incorrectly as being asleep, and thus the technique is biased toward overestimating time to sleep, which may lead to incorrectly minimizing the severity of sleep disturbances.”
There are multiple other issues and questions with the usefulness of the data that Oura provides that need clarifying before the ring can be considered useful.
For example, the SRI paper found significant differences in results depending on which finger the ring was placed on, with greater discrepancies for “light sleep” and REM on the ring finger compared to the other fingers.
The in-house Oura study also noted that results were more accurate on the non-dominant hand finger compared to the dominant hand, but the Oura website makes no recommendation on which finger to use.
The other data that Oura compiles (heart rate, heart rate variability, temperature change, respiration) are clearly related to sleep cycles but Oura provides no evidence that these data or their proprietary algorithms to give you “readiness” or sleep quality scores are accurate or of any value.
Should You Buy An Oura Ring?
If you are hoping to get improved analysis of your sleep quality, I don’t think Oura adds anything to what is elsewhere available using cheaper wrist actigraphy devices.
The ring is expensive at $299 and cannot accurately detect sleep stages.
Although most reviews you will encounter on the internet are wildly enthusiastic about Oura, they are likely biased and provide no evidence that the unique aspects of the ring sensors provide useful information.
Would I buy it again?
I’ve misplaced my ring several times and I have to say that this distressed me immensely. Given that I think the sleep analysis is worthless, this is hard to explain.
I think my attachment to the ring is due to a number of factors: It’s stylish and it mimics a wedding ring (which I otherwise do not have).
I’m intrigued by some of the cardiovascular data it produces (nighttime heart rate and heart rate variability). Although I don’t think the data can guide me to healthier behavior, it’s possible that there is useful information in there somewhere. I hope to write a post on heart rate variability down the line. I’ve done research in this area and have some strong opinions on its value.
I’m curious to see if the respiratory rate data and the temperature data is of any value whatsoever.
So, the ring is best I would say for well-heeled, self-hacking, and self-experimenting techno geeks.
Anthony Pearson, MD, is a private practice noninvasive cardiologist and medical director of echocardiography at St. Luke’s Hospital in St. Louis. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at The Skeptical Cardiologist, where a version of this post first appeared.