Sleep is one of the most important components of living a healthy lifestyle. It is no wonder that it has become yet another target of modern technology and big data. When Fitbit released their sleep tracking function on their wearable devices in 2017, they unlocked a trove of biomedical data that allows us to understand more about sleep habits.

What do they measure?

Fitbit sleep trackers are capable of monitoring and measuring sleep through their wearable wrist devices. All of their wrist devices automatically detect sleep by detecting users’ movement. For instance, when the device does not detect movement for about an hour, it assumes that you have fallen asleep.

Additional movements like rolling over during sleep are detected by the device and confirm the assumption that you are truly asleep. Morning activity signals to the device that you are no longer sleeping.

fitbit watch and the sleep tracker data

Some of Fitbit’s wrist devices are equipped with heart rate monitors and can detect more detailed and precise data about sleep patterns. For instance, heart rates tend to lower during sleep, and they gradually decrease in the first cycles of sleep. At about the halfway point of a full night’s sleep, heart rates tend to gradually increase again to prepare the body to wake up. Throughout the cycles, heart rates also tend to spike during REM sleep. A Fitbit can detect these patterns to determine approximate sleep cycles and the quality of sleep.

Although the Fitbit sleep tracker is accurate in the metrics that it does monitor, it is limited in the number of metrics it can track that may contribute to the quality of sleep. This means that the results are accurate only to the extent of what they track. Although this basic information is reliable, it must be understood that it is not necessarily complete because there are several other factors that contribute to sleep quality.

Fitbit Sleep Data

With all this data on sleep patterns, what does Fitbit do with all this information? The sleep data accumulated across all Fitbit users surpassed six billion nights of sleep as of early 2018. This is an impressive and unprecedented data set that has revealed interesting habits among American adults.

The first significant observation that data scientists with Fitbit made is that women, on average, get more sleep than men by clocking in about six hours and fifty minutes of accumulated time asleep per night. This is compared to an average for men of about six hours and twenty-six minutes of time asleep per night. Women also get about ten extra minutes of REM sleep per night compared to men.

The most significant finding of Fitbit’s data, however, is the observed correlation between sleep quality and bedtime consistency. The data scientists found that the average sleep time of Americans varies by about an hour. This variability impacts the quality of sleep, which the scientists attribute to “social jet lag.” People whose bedtime varies by two hours over the week average a half-hour of sleep a night less than people whose bedtime only varies by about a half-hour.

Next time you stay out late on a weekend night you may want to consider that the feeling on Monday morning is not just residual from the weekend hangover. It is also a result of “social jet lag” from bedtime variability.

How does exercising before bed affect your sleep patterns? We dive into that topic here.