It is estimated that one in three people regularly reports sleep complaints. It is therefore not surprising that people are more worried than ever about getting enough sleep. This thriving interest has seen an explosion of sleep trackers measuring how many hours of sleep you get each night.
While we sleep, we go through sleep of cycles of “deep”, “light” and “rapid eye movement” (REM). The ‘deep’ part of our sleep is especially what makes us feel refreshed the next day. Most sleep trackers are a watch worn on the wrist and work by monitoring your body movements while you sleep to determine how much time you are likely to be awake while sleeping. Some devices also look at the heart rate changes during sleep to estimate how much time you spent in each sleep cycle.
Despite their popularity, only a few studies have examined how accurate sleeping devices are. So far, research has found that sleep trackers 78% of the time are just as accurate as they identify sleep versus wakefulness, compared to polysomnography tests – which experts use to diagnose sleep disorders. This accuracy drops to about 38% when we estimate how long it took participants to fall asleep.
Polysomnography tests are the most accurate because they track brain waves, heart rate, respiration, blood oxygen levels and body and eye movements during sleep using electrodes attached to the skin and scalp. Analyzing brainwave patterns is the only definitive way to know if someone is awake or asleep, and to know at what stage of sleep they are.
But since sleep trackers are worn on the wrist, they make their estimate of night sleep by measuring body movement and sometimes heart rate data. Since we regularly move in all stages of sleep, movement offers little indication of what stage of sleep we are. Many sleep programs also cannot distinguish some stage of sleep based on movement alone.
Since many sleeping devices for consumers have not been compared with polysomnography tests, it is difficult to determine their accuracy rate. Furthermore, the algorithms that companies use to make predictions about sleep are unknown, making it difficult for scientists to determine whether the assumptions made by the sleep devices are valid.
Studies also show that sleep devices underperform in people with insomnia. People with insomnia tend to stay very quiet in bed in an attempt to fall asleep. But since sleep problems only measure movement, one study found that watches could not distinguish sleep from wakefulness in people with insomnia.
Watches that contain heart rate data tend to be slightly more accurate when measuring sleep duration, because heart rate varies during different sleep stages. However, even in devices that do detect heart rate, many experts are still unsure about their accuracy, due to the limited research on it and due to the differences between each device. One study of heart rate trackers, for example, showed that two consuming devices tended to underestimate the amount of deep sleep carriers achieved up to 46 minutes.
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Ultimately, this leads to the question of whether knowing our sleep is beneficial to us. After all, one of the best ways to stay awake is to try hard to sleep. It sounds counter-intuitive, but we see it clinically in patients with chronic insomnia, for whom excessive pre-occupation with sleep anxiety and low mood causes due to sleep loss – leading to further insomnia.
A study published by our research group showed that the effect can be exacerbated by sleep clocks. Participants were given sleep guards and were asked to complete the state of mind, day processes and drowsiness during regular periods during the day. However, the “sleep count” that their watches gave was manipulated to show an increased or a decreased quality of sleep. The quantity and quality of the sleep participants in both groups were the same.
The study found that those who told them they had a bad night’s sleep, had a lower mood, problems with thought processes during the day and increased sleepiness. Those who told them they slept well showed the opposite.
It shows us that the data from these sleep detectors can change your emotional state and concentration levels during the day – even if the readings are accurate. As people who sleep poorly are more likely to use sleep tracking devices, this can be a cause for concern as it can exacerbate mental health problems.
Although few studies have examined this link so far, one report has highlighted that more patients are seeking treatment for suspected sleep problems due to feedback from sleep trackers. Even when such complaints are refuted by a polysomnography test, watches remain a source of sleep-related anxiety. As studies show that the use of portable devices (such as those used during exercise) increases health anxiety and depression, there is concern that sleeping devices may have a similar effect.
Although sleeping devices can be useful for those who generally sleep well, but who are interested in finding a better routine, people who have poor sleep or mental health can avoid it. But the best measure to measure how well you slept was to see how you felt each day. If you are tired and have difficulty concentrating, it can help you feel more rested to go to bed a little earlier each night – no device needed.
This article by Matthew Reid, PhD Researcher, Sleep and Circadian Neuroscience, University of Oxford, was published from The Conversation under a Creative Commons license. Read the original article.
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Published on January 17, 2021 – 09:00 UTC