What Is Core Sleep? Unpacking The Misunderstood Sleep Metric

If you use a sleep tracker, there's a chance you've seen "core sleep" show up in your morning report. The thing is, core sleep isn't an officially recognized sleep stage, which makes figuring out what to do with your reading a little confusing.

Sleep specialists generally use the term "core sleep" as a reference to the minimum amount of sleep needed to function throughout the day, Silverman explains.

But some older research studies2 have also used "core sleep" to reference the deep sleep stages of REM and NREM Stage 3 sleep.

How much core sleep you need every night depends on a few key factors, such as your age, health, lifestyle, etc. It also depends on which definition of core sleep you’re adhering to.

Sleep needs are largely personal, but the Centers for Disease Control and Prevention (CDC)3 recommends adults between the ages of 18 and 60 get seven or more hours of total sleep per night for optimal functionality.

Silverman says between 45-50% of this time should be spent in deeper sleep stages, and the rest of your night can be in those lighter NREM1 and NREM2 stages.

It’s worth noting, however, that your sleep architecture might change as you age. Silverman reminds us that, compared to kids and teenagers, adults spend less time in deeper sleep stages and even less time after age 65.

Your sleep space should be just that: a space dedicated to sleeping. Per the National Sleep Foundation, mastering sleep hygiene, which includes your sleep environment, is key to improving your overall sleep quality.

Another way to achieve A+ sleep hygiene is by setting and following a sleep schedule. If you’re going to bed at 9 p.m. one day and midnight the next, with the rest of the week in a similar pattern of disarray, your circadian rhythm is likely confused.

If you’re thirsty before bed, have a few sips of water to quench your thirst, but don’t down an entire glass (or two).

Using your phone too close to bed keeps your brain awake, thanks to the way blue light mimics daylight. It also puts you at risk of consuming content that can cause unnecessary stress.

A study published in the journal PLOS ONE6, in which participants had restricted phone access before bed for four weeks, found an increase in sleep duration and quality, among other benefits.

While it can be beneficial to track your sleep (after all, knowledge is power, especially when it comes to your health), not all sleep experts recommend it.

Silverman, for example, says that, as an insomnia specialist, she doesn't suggest sleep trackers for her patients. "Sleep wearables aren’t able to differentiate between sleep and wake very well in individuals with insomnia," she notes.

People who are vulnerable to becoming unhealthily obsessed with the numbers may also want to avoid data tracking.

"Sleep tracking and focusing too much on the data can often lead to more worry about sleep, as I tend to see a lot of individuals who develop 'orthosomnia,' or an unhealthy obsession with achieving perfect sleep due to becoming fixated on the sleep stages," Silverman says.

"Most commonly, it is a fixation on whether there was enough REM or deep sleep during the night," Silverman continues, adding that this behavior can quickly become counterproductive. "It increases worry about sleep and tends to lead to a lack of self-trust or confidence in your ability to sleep well."

The accuracy of these trackers’ data is also cause for concern. According to Peirson, the only truly reliable way to measure your time in each sleep stage is polysomnography, or a sleep test performed in a lab that, measures "your brain waves, the oxygen level in your blood, and your heart rate and breathing during sleep."

There is no universal definition for "core sleep." Some sleep experts use it as shorthand for the amount of sleep someone needs each night to function the next day (it's a little different for all of us). Some sleep trackers measure core sleep as the amount of time you spend in lighter sleep stages (NREM1 and NREM2).

No matter which definition you follow, enhancing your core sleep likely involves cleaning up your overall sleep routine so you spend an appropriate amount of time in each sleep stage.

You can do this by using less tech before bed, following a steady bedtime and wake-up time, watching what you eat and drink at night, or following a number of other sleep-promoting tips.

You can measure how you're tracking towards your goals with a wearable sleep tracker. Just remember that they're not 100% accurate and stressing over the numbers too much could do more harm than good. Simply clocking how you feel when you wake up and go about your day will also give you an idea of your sleep quality.