Study finds Fitbit heart rate-tracking devices to accurately track sleep stages

Analysis of over 4 billion nights of Fitbit sleep data supports scientific theories that sleeping 7+ hours can positively affect sleep quality.

Study finds Fitbit heart rate-tracking devices to accurately track sleep stages

It has been a lot of talk about the accuracy of wrist-worn fitness trackers, including that recent Stanford study that found most devices fail to accurately track calorie consumption. Fitbit is reacting now with a newly released study that proves its devices can accurately determine light, deep and REM sleep stages.

The results of the study, which were scored independently by polysomnography technicians, demonstrate that Fitbit activity trackers can be used to track sleep stages with a reasonable degree of accuracy in normal adult sleepers, avoiding the cost and artificial sleep environment of a sleep laboratory.

"With our sleep tracking tools, Fitbit has transformed what people can learn about their sleep habits by taking the ability to track sleep stages out of a lab and putting it on the wrist," Dr. Conor Heneghan, lead sleep research scientist at Fitbit, said in a statement. "The ability to easily track your sleep not only helps individuals better understand their own sleep, it also unlocks significant potential for us to better understand population health and gain new insights into the mysteries of sleep and its connection to a variety of health conditions."

In April 2017, Fitbit introduced new sleep features to provide people with a greater understanding of their sleep habits. Sleep Stages — now available with Alta HR, Blaze and Charge 2 — uses heart rate variability to estimate the amount of time spent in light, deep and REM sleep, as well as time awake each night to help better recognize sleep quality.

With more than four billion nights of sleep tracked since 2010, Fitbit has the most extensive, longitudinal database on sleep in the world. The company recently conducted an analysis of millions of nights of anonymized and aggregated Fitbit sleep stages data that supports long-standing sleep scientists' theories that sleeping more than seven hours a night is best for your health. Leading sleep researchers have linked getting less than seven hours of sleep to a reduction in REM sleep, which could impact short-term memory, cell regeneration and mood regulation.

Fitbit analysis has found that sleeping 7-8 hours gives you the highest combined percentage of time in deep and REM sleep stages. In contrast, sleeping less than 7 hours will lead to deep and REM stages being a smaller proportion of your overall sleep. Related, waking up earlier than usual can impact the percentage of REM sleep you get, which occurs more at the end of the night.

When getting five hours or less of sleep a night, users get a smaller percentage of deep sleep, which occurs near the beginning of the night. Deep sleep is important for many physical processes such as cell regeneration, human growth hormone secretion and feeling refreshed in the morning.

Finally, Fitbit has found that 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.

Fitbit also evaluated sleep patterns by gender and generation: Gen Z (age 13-22) sleeps the most, averaging 6 hours and 57 minutes of sleep a night with 17% of the time in deep sleep, while Baby Boomers (age 52-71) sleep the least at 6 hours and 33 minutes per night with 13% of the time in deep sleep.

Further, the study has found that people get less deep sleep as they age, decreasing from an average of 17% at age 20 to 12% at age 70. Gender wise, women sleep an average of 25 more minutes a night than men and have a higher percentage of REM sleep, a difference which increases even further around age 50.

"When sleeping less than seven hours, your body may not be getting enough of both deep and REM sleep, the two sleep stages that are very important to many aspects of maintaining your overall health," said Dr. Michael T. Smith, Jr., professor of Psychiatry, Neurology and Nursing at Johns Hopkins University School of Medicine and Fitbit Advisory Panel Sleep Expert.

Previous sleep research has shown that most people spend 50-60% of their night in light sleep, 10-15% in deep sleep, and 20-25% in REM sleep. Fitbit analysis shows that age and gender impact your sleep cycle, and confirm that most people typically lie within these ranges on average over 30 days. Night-to-night sleep cycles may vary widely.

 Light SleepDeep SleepREM SleepTotal Duration
Female Baby Boomers (Age 52-71)53.50%13.00%21.30%6 hrs 42 mins
Female Gen X (Age 41-51)52.20%14.40%21.70%6 hrs 46 mins
Female Millennial (Age 23-40)51.00%15.50%21.70%6 hrs 53 mins
Female Gen Z (Age 13-22)49.90%16.80%21.40%7 hrs 6 mins
Male Baby Boomers (Age 52-71)54.80%12.80%19.90%6 hrs 23 mins
Male Gen X (Age 41-51)52.30%14.60%21.00%6 hrs 22 mins
Male Millennial (Age 23-40)50.80%16.00%21.10%6 hrs 28 mins
Male Gen Z (Age 13-22)49.80%17.30%20.60%6 hrs 47 mins
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