Is there really any benefit to tracking your sleep?

It’s a logical step, since scientists have learned that sleep plays a huge role in nearly every aspect of our wellbeing. Numerous studies have associated better sleep with lower heart risks, better athletic performance, even higher libido, among other benefits.

So there’s no argument that sleep is important. But, are those fitness trackers really telling you the full story when it comes to your shuteye?

Well, the data you’re getting definitely can be useful, believes W. Chris Winter, M.D., Men’s Health sleep adviser and author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It.

Here’s what these trackers are doing: The devices don’t directly measure sleep quality—you’d need a sleep lab study for that—but do track movement.

That’s a decent surrogate of sleep, since you do tend to be still when you’re sleeping, Dr. Winter says. In fact, in a dream state, your body typically enters temporary sleep paralysis to protect you from acting out those dreams, he says.

Sleep trackers have been used in some form for decades, he adds, and do a good job of providing insight about someone’s sleep patterns over time, like how much total time you’re probably sleeping.

That means looking at how well you slept last night probably won’t be useful, but it can be very helpful to see patterns over the space of a few weeks or months. For example, says Dr. Winter, trackers are used for shift workers to see how well they stick to a sleep schedule.

“These trackers are mainstays in shift work, jet lag, and circadian rhythm research,” he says. That’s because they can tell things like whether it’s taking you a long time to fall asleep, or if you’re waking earlier than you should.

There are some limitations, though. Dr. Winter says that they’re not great at determining sleep stage—in general, you can track mainly whether you’re asleep or not, but not factors like how long it takes you to get into REM sleep, when you’re dreaming, or pre-REM sleep when your body is preparing for that deeper stage.

That’s important, since REM sleep is required for a number of restorative processes in your brain and body, Dr. Winter says. The National Sleep Foundation notes that all of the phases of sleep are needed for muscle repair, memory consolidation, and release of hormones regulating growth and appetite.

Also, there’s concern that the devices overestimate sleep when your body is still and your heart rate has slowed, but you’re not actually asleep, adds Isha Gupta, M.D., a neurologist at IGEA Brain & Spine. Still, he says, the devices offer a good way to gain an overall idea of how often you wake up at night, and how long it takes you to fall asleep—data that can help you tweak habits, such as setting an earlier bedtime or keeping your bedroom cooler.

When considering how to use the tracking data, it’s also important not to overthink the results, advises Nancy Foldvary, M.D., who heads up sleep medicine at Cleveland Clinic. If you’re getting between seven to nine hours of sleep per night and feel refreshed and energized during the day, then concerns raised by your tracking device may not be clinically important.

“In other words, how you feel after a night of sleep is generally the best measure of sleep health,” Dr. Foldvary says.

Sleep Better than Ever with the Smart Headband from Philips at CES2018:

On the other hand, if you’re getting the recommended amount of sleep and still feel lousy, you may have sleep issues that a tracker wouldn’t pick up on, she adds. That might include medical conditions like heart disease, thyroid issues, or sleep apnea. Dr. Foldvary advises talking to your doctor to go over possible reasons, so you can go back to getting the sleep you need.