Fitbit's Rem Sleep Tracking: A Premium Feature?

Fitbit devices can track your sleep by monitoring your movement and heart-rate patterns. When you haven't moved for about an hour, your Fitbit assumes you're asleep. It also uses heart rate variability (HRV) to determine the stages of sleep you are in. While the basic sleep tracking functions are available through the standard Fitbit app, some features, like a sleep profile, are only available on Fitbit Premium, which costs $10 a month.

Fitbit's accuracy in tracking sleep stages

Fitbit devices that track heart rate (except Charge HR and Surge) can also track sleep stages. Fitbit estimates sleep stages by using movement and heart-rate patterns. When the user hasn't moved for about an hour, the device assumes they are asleep. It also tracks the beat-to-beat changes in the user's heart rate, known as heart rate variability (HRV), which fluctuates as they transition between light sleep, deep sleep, and REM sleep stages.

According to a paper published by Fitbit scientists in 2017, the watch's sensors can classify sleep stages with 69% accuracy in any given 30-second time window. While this may seem low, there is no systematic bias to how much light sleep, deep sleep, or sleeplessness Fitbit estimates. In other words, Fitbit does not over- or underestimate the duration of these stages. This means that if you use the app for many nights, you will eventually get a good sense of how often you tend to be awake, lightly asleep, or deeply asleep on a typical night.

Fitbit has tracked more than 4 billion nights of sleep since 2010. It recently conducted an analysis of millions of nights of anonymized and aggregated Fitbit sleep stages data that supports theories that sleeping more than 7 hours a night is best for health. The analysis also found that:

• While sleeping longer will lead to getting more deep and REM sleep, sleeping 7-8 hours gives the highest combined percentage of time in these stages.
• Sleeping less than 7 hours will lead to deep and REM stages being a smaller proportion of overall sleep.
• Waking up earlier than usual can impact the percentage of REM sleep, which occurs more at the end of the night.
• When getting 5 hours or less of sleep a night, users get a smaller percentage of deep sleep, which occurs near the beginning of the night.
• People are unconsciously awake at night; the average awake time adds up to 55 minutes, or 10%-15% of the night. Short periods of awake time are a normal component of a healthy sleep cycle.
• People get less deep sleep as they age, decreasing from an average of 17% at age 20 to 12% at age 70.
• Women sleep an average of 25 more minutes a night than men and have a higher percentage of REM sleep, a difference that increases even further around age 50.

The science behind sleep tracking

Sleep tracking is a feature available on Fitbit devices that can help users understand their sleep patterns and quality. This feature is particularly useful as getting sufficient and good-quality sleep is an important but often underappreciated component of health. Sleep is essential for draining the brain of toxins linked to Alzheimer's disease and for consolidating memories from the day before.

Fitbit devices with heart-rate tracking (excluding the Fitbit Charge HR and Surge models) can track sleep stages, including light sleep, deep sleep, and REM sleep. While you sleep, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuates as you transition between the different sleep stages. When you sync your device in the morning, it uses your movement and heart rate patterns to estimate your sleep cycles from the previous night.

The Fitbit Versa, for example, infers when you're sleeping and what stage of sleep you're in by using an accelerometer, which measures bodily accelerations of the wrist, coupled with a technique called optical photoplethysmography (PPG), which measures blood flow based on how green light from an LED on the back of the watch is reflected by the body.

Fitbit's sleep tracking feature can help users identify if they are getting enough sleep and the quality of their sleep. For instance, if a user finds that they are getting less sleep than expected, they can make adjustments to their sleep schedule to get more rest. Additionally, Fitbit's sleep data can provide insights into sleep patterns, such as the amount of time spent in each sleep stage and sleep duration.

It's important to note that while sleep tracking can be informative, it should not be the sole source of sleep analysis. Sleep experts recommend that sleep trackers should be used in conjunction with good sleep hygiene practices, such as maintaining a regular sleep schedule and sleeping in a cool, quiet, and darkened room.

The importance of REM sleep

REM sleep is the fourth and final stage of the sleep cycle, characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity. It is also known as active sleep, desynchronized sleep, paradoxical sleep, rhombencephalic sleep, and dream sleep.

REM sleep is important for several reasons:

• Dreaming: The majority of dreams occur during REM sleep, and these dreams are usually more vivid than those that occur during non-REM sleep.
• Emotional Processing: The brain processes emotions during REM sleep, and the amygdala (the part of the brain that processes emotions) is activated.
• Memory Consolidation: During this stage, the brain processes new learnings and motor skills from the day, committing some to memory, maintaining others, and deciding which ones to delete.
• Brain Development: Researchers hypothesise that REM sleep promotes brain development, as newborns spend most of their sleep time in this stage.
• Wakefulness Preparation: REM sleep may help prepare the body to wake up, which could explain why it occurs mostly in the second half of the night, and why it is easier to wake up during this stage.
• Mood Regulation: REM sleep helps the brain process emotional memories, including those associated with fear, which may aid in mood regulation.
• Protection Against Dementia: According to a study published in the journal Neurology, people who get less REM sleep have a higher risk of developing dementia.

How to improve sleep quality

Sleep is a core component of health and well-being. Here are some tips to improve your sleep quality:

• Invest in a good mattress and bedding: A supportive mattress and pillow are vital to ensuring you get a good night's sleep. Your bed should provide proper support to avoid any aches and pains. Sheets and blankets that feel comfortable and help maintain a good temperature are also important.
• Optimise your bedroom environment: Keep noise, light, and artificial lights from devices to a minimum. The ideal bedroom temperature is subjective, but most people sleep best in a slightly cooler room, around 65-68°F (18.3-20°C).
• Stick to a sleep schedule: Try to go to bed and wake up at the same time every day, even on weekends. This helps your body get accustomed to a healthy sleep routine.
• Limit naps: Naps can be beneficial, but long or irregular naps during the day can negatively affect your nighttime sleep. Aim for a 20-minute power nap in the early afternoon if you need one.
• Relax before bed: It's easier to fall asleep if you're relaxed. Try reading, stretching, listening to soothing music, or relaxation exercises. Controlled breathing, mindfulness meditation, progressive muscle relaxation, and guided imagery are all methods that can help ease you into sleep.
• Disconnect from devices: The light from electronic devices can suppress your natural production of melatonin. Try to disconnect for at least an hour before going to bed.
• Get natural light exposure: Sunlight has a strong effect on your body's internal clock, so try to get outside or expose yourself to natural light during the day.
• Exercise regularly: Daily exercise has many benefits for health and can promote solid sleep. However, avoid intense exercise close to bedtime as it may hinder your body's ability to settle down.
• Avoid caffeine and alcohol late in the day: Late caffeine consumption reduces total sleep time and overall sleep efficiency. Avoid caffeinated drinks at least 8 hours before bedtime. Alcohol can induce drowsiness, but it lowers sleep quality, so avoid drinking alcohol close to bedtime.
• Eat dinner a few hours before bed: It's harder to fall asleep if your body is still digesting a big meal. Avoid late dinners and limit fatty or spicy foods. If you need a snack, opt for something light.
• Consider supplements: Melatonin supplements are a popular sleep aid and may help you fall asleep faster. Other natural sleep aids include valerian, chamomile, and glycine. Always check with a healthcare professional before taking any supplements.

The cost of accessing sleep data

Fitbit offers a range of fitness trackers and smartwatches that can monitor your sleep. While the basic sleep-tracking features are available for free, accessing more advanced sleep insights comes at a cost.

Basic sleep tracking

All Fitbit devices can track your sleep in terms of duration. They can also detect when you are asleep by sensing periods of inactivity and changes in your heart rate. This data is then synced to the Fitbit app, where you can view your sleep stats, including the time you went to bed, the time you woke up, and how much time you were awake during the night.

Sleep stages

Fitbit devices with heart rate monitors can provide more detailed sleep insights by differentiating between light sleep, deep sleep, and REM sleep. This is done by using an accelerometer and optical photoplethysmography (PPG) to measure bodily movements and blood flow. However, this feature is limited to newer devices launched in the last few years.

Sleep profiles

Fitbit offers a monthly Sleep Profile feature, which provides a more comprehensive breakdown of your sleep patterns. This includes metrics such as sleep schedule variability, time before falling asleep, sleep duration, REM sleep, and sleep stability. However, this feature is only available on specific models, including the Charge 5, Charge 6, Inspire 2, Inspire 3, Luxe, Sense, Versa 2, Versa 3, and Google Pixel watches. Additionally, a Fitbit Premium subscription is required to access Sleep Profiles.

Premium subscription

The Fitbit Premium subscription costs $10 per month and unlocks a range of extra insights, not just for sleep but also for other areas such as fitness and meditation. It also provides access to a library of workout videos, guided meditations, sleep aids, and audio tracks for runs or workouts.

Accuracy and limitations

While Fitbit's sleep tracking can provide valuable insights, it is important to note that it may not be as accurate as polysomnography, which is the technique used by doctors and scientists to determine sleep stages. Fitbit's sensors can classify sleep stages with 69% accuracy in any given 30-second time window. Additionally, the SpO2 sensor, which has the potential to provide valuable feedback to sleepers with sleep apnea, is currently not utilised by the Fitbit app and awaits government approval.

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