Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Fitness Trackers Offer an Abridged Analysis of Sleep Patterns

Dear Doctors: I understand how my fitness tracker counts my steps and measures my heart rate, but supposedly it can say how well I sleep. How can it do that, and is that sort of data even accurate?

Dear Reader: We’ve seen a boom in the popularity of health tracking devices in recent years. A poll conducted last year found that 1 in 3 Americans has tried out some form of health tech, and that close to 20% of us now use a digital fitness tracking device each day. Depending on the specific device, wearables can count the number of steps we take each day, log our heart rate, analyze stress, count how many flights of stairs we have climbed, pinpoint the amount of time we’ve spent being active, estimate how many calories we’ve burned, measure distance traveled or use UV sensors to measure sun exposure. And, yes, a growing number of devices now follow us into the bedroom to monitor and analyze our sleep.

Many wearables, like the one you use, include a sleep mode. Again, depending on the device, they may offer information about how long you sleep, or about the quality of that sleep. They do this using sensors known as accelerometers, which can detect not only when someone is moving but also the speed and direction of that motion. This data, along with the heart rate information that the device collects, is extrapolated into sleep analysis. Some trackers even claim to be able to quantify how much time has been spent in the three major phases of sleep -- light sleep, deep sleep and REM sleep.

It’s important to note that for accurate sleep analysis, you need an overnight stay at a sleep lab. There, electrodes are placed on the face, scalp, chest and limbs to digitally collect and record a range of activities in both the brain and the body. The information that goes into analyzing your sleep includes breathing, physical motion, muscle tone, eye movement, heart rate and rhythms, and brain wave activity. Fitness trackers, by contrast, are limited to the motion and heart rate data that they are able to collect, which is then parsed by an algorithm. Sleep experts are concerned that someone with a sleep disorder who relies on the data from a fitness tracker may inadvertently be reassured that all is well. The flip side is that someone with no sleep problems at all may become worried about data that isn’t necessarily accurate.

The bottom line is that a fitness tracker with a sleep mode can be good at letting you know how long you were motionless, how often you were restless and how many times you got up during the night. However, it’s not information that reliably translates into sleep quantity or sleep quality. Anyone who thinks they may have a sleep disorder, or who wants to improve the quality of their sleep, should first check with their health care provider. Then, if it’s appropriate, a night in a sleep lab may be the next step.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)