What’s the deal with sleep trackers?

Health tech is ever evolving, and trackers such as FitBit and smartwatches are something that has been adopted by anyone serious about looking after their health. These trackers and associated apps can monitor everything from heart rate to dietary intake.

Many people also use these devices to monitor their sleep, even more so as research begins to unveil the true impact of not sleeping well. However, the accuracy of these trackers to monitor sleep accurately has come into question. In some cases, an overreliance and obsession over the data they provide have led to further sleep issues.

How much sleep do you need?

Current advice around sleep is that the average healthy adult needs 6-9 hours a night¹. Like everything related to health, there is no ‘one-size-fits-all’ for sleep and indeed no magic number. The variability in sleep times between individuals may be down to genetics and numerous other lifestyle factors. In fact, a decade ago, researchers discovered a genetic mutation in some people linked to short sleep, meaning they got the same benefit on six hours of sleep as those without the mutation who got eight². Since then, several other similar genes have been discovered, contributing to the evidence that functioning well on less sleep is a genetic trait.

Research is ever evolving around sleep. There is plenty to suggest that a lack of it is linked to an increased risk of heart disease, high blood pressure, stroke, obesity, type 2 diabetes, depression, and anxiety³. However, the definition of ‘lack of sleep’ varies between individuals, so it’s wrong to assume that there will be health consequences if you get less than eight hours a night. It is also not just about total sleep time but sleep quality.

What are the stages of sleep?

Four sleep stages make up a single cycle that lasts around 90 minutes and the number of cycles that occur is dependent on how long you are asleep.

Stage one is short only lasting 5-10 minutes. Sleep is shallow during this stage, and while your brain is dipped into sleep, you may not feel as though you are asleep. This is the stage at which you can be easily woken.

Stage two is often referred to as light sleep. It’s an important stage that takes up much of the night and is characterised by a slowing down of breathing and heart rate. During the first sleep cycle, this stage lasts around 10-25 mins but increases during subsequent cycles to make up half of the time you spend asleep.

Stage three is deep sleep, and it is difficult to wake people up from this stage in the cycle. The body totally relaxes during this stage, and your pulse and breathing rate drops even further. This stage is restorative and essential for recovery and growth and bolstering the immune system. The body is vulnerable during this stage, so after the first couple of sleep cycles, the time spent in this stage reduces as you spend more time in REM sleep.

The final stage of sleep is REM. During this stage, the body is inactive, but your eyes move rapidly hence the name. Heart rate increases and breathing becomes more irregular during this stage. Bodily functions such as protein synthesis peek at this stage, which is also when you are most likely to dream. This stage is also essential for cognition, learning, and creativity.

So, back to sleep trackers.

How do sleep trackers monitor sleep?

Sleep trackers monitor sleep by movement and heart rate, but their accuracy is certainly not 100%. Just because you’re not moving doesn’t necessarily mean you are asleep, which is a flaw in the tech. Wearables that monitor heart rate are likely to be a little more accurate at defining between the sleep stages as it fluctuates between them.

Only a few studies compare the accuracy of sleep monitoring devices set against the recognised lab testing called polysomnography, which looks at brain waves, blood oxygen levels, heart rate, breathing, and eye and leg movements. One such study published in the journal Sleep Medical Reviews found that sleep trackers were only accurate 78% of the time when identifying sleep versus wakefulness. This accuracy dropped to just 38% when estimating how long it took participants to fall asleep⁴.

What information do sleep trackers provide?

Most sleep trackers will tell you how long you were asleep and awake during the night. The data is also broken down into the different stages of sleep, and how well you slept is given as a percentage score. This data is helpful to help identify your sleep pattern and provides a way of monitoring your sleep over time.

How people interpret, this data is an issue with these trackers. Most people do not understand how sleep cycles work and how the timing of each stage varies during the night. A common misconception is that you should be getting lots of deep sleep when this is the stage you spend the least time in during the night.

Sleep trackers also have no way of assessing exactly how much sleep you need. Most trackers give you a higher score for getting closer to eight hours a night, but this is misleading if you only need six hours to function optimally.

Can sleep trackers do more harm than good?

While the information provided by sleep trackers can be helpful, it can’t be relied upon to give you an accurate analysis. In some instances, people have become too focused on this data in their quest to achieve the perfect sleep score. This obsessive focus can cause anxiety and unhealthy sleep behaviours, ironically disrupting sleep.

Researchers have coined the term ‘orthosomnia’ to describe the potential risks associated with people who develop an unhealthy preoccupation with improving the data from their sleep tracker⁵. Studies on the topic have shown how people self-diagnose and convince themselves they have a sleep disorder based on their sleep data even though they may not⁵. The knock-on effect is increased stress and time and money wasted investigating the issue.

Some people may also spend excessive time in bed to improve their sleep scores. The problem with this behaviour is that it reinforces poor sleeping habits and can condition the body for sleeplessness, leading to future issues with insomnia further down the line.

How useful are sleep trackers?

Sleep trackers provide some helpful insight into your sleep patterns, and they offer a way to monitor this over time. They won’t help you get a better night’s sleep, as this is down to good sleep hygiene habits.

The problem with many health techs is that it needs to be programmed around a set of algorithms based on generic data or information imputed by the user. As far as sleep is concerned, wearables do not have the functionality to establish precisely how much sleep you need to function at your best. Research has shown how people become more reliant on their tracker to tell them whether they got a restful sleep. The only way to figure this out is by listening to your own body. Rather than focusing too much on numbers, it is better to assume you are getting enough sleep if you wake up fully rested and perform well during the day.

References

1. Hirshkowitz, M., Whiton, K., Albert, S. M., Alessi, C., Bruni, O., DonCarlos, L., Hazen, N., Herman, J., Katz, E. S., Kheirandish-Gozal, L., Neubauer, D. N., O’Donnell, A. E., Ohayon, M., Peever, J., Rawding, R., Sachdeva, R. C., Setters, B., Vitiello, M. V., Ware, J. C., & Adams Hillard, P. J. (2015). National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep health, 1(1), 40–43.
2. Shi, G., Xing, L., Wu, D., Bhattacharyya, B. J., Jones, C. R., McMahon, T., Chong, S., Chen, J. A., Coppola, G., Geschwind, D., Krystal, A., Ptáček, L. J., & Fu, Y. H. (2019). A Rare Mutation of β₁-Adrenergic Receptor Affects Sleep/Wake Behaviors. Neuron, 103(6), 1044–1055.e7.
3. Nagai, M., Hoshide, S., & Kario, K. (2010). Sleep duration as a risk factor for cardiovascular disease- a review of the recent literature. Current cardiology reviews, 6(1), 54–61.
4. Conley, S., Knies, A., Batten, J., Ash, G., Miner, B., Hwang, Y., Jeon, S., & Redeker, N. S. (2019). Agreement between actigraphic and polysomnographic measures of sleep in adults with and without chronic conditions: A systematic review and meta-analysis. Sleep medicine reviews, 46, 151–160. https://doi.org/10.1016/j.smrv.2019.05.001
5. Baron, K. G., Abbott, S., Jao, N., Manalo, N., & Mullen, R. (2017). Orthosomnia: Are Some Patients Taking the Quantified Self Too Far?. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 13(2), 351–354.