A good night’s sleep — what your device is telling you about your rest
At a glance
- The accuracy of wearable devices that track sleep-related data varies
- What’s most important is how you feel when you wake up
- It’s worth paying attention to your blood oxygen saturation and heart rate variability
“Get a good night’s sleep” is advice you’ve likely heard before — and for good reason. Sleep quantity and quality affects nearly every aspect of our lives, from our mood to our physical health to our performance at work or school.
But what qualifies as a “good night’s sleep”?
Many of us have turned to technology to answer this question. Numerous wearable devices on the market claim to track sleep-related data. How useful is this information in determining how well you sleep?
The answer — it depends.
“The accuracy of these devices can vary,” says Kimberly Mebust, MD, a sleep medicine specialist at MultiCare Health System. “Accuracy depends on the particular algorithm used to track your sleep, how the device was tested, your age, whether you have a sleep disorder and other factors. The data can be useful, but what’s more important is how you feel when you wake up. Are you refreshed, alert and ready to start your day?”
While how you feel outweighs what your device may report, learn more about what your device is telling you and what data to pay close attention to.
The four stages of sleep
Sleep is divided into four stages, and each benefits the body and the mind. We cycle through these stages approximately three to five times per night.
Stages 1 and 2. These two stages are considered light sleep. Our body temperature drops, muscles relax, and heart rate and brain activity slow down. Adults spend approximately 45-55 percent of their sleep each night in stage 2.
Stage 3. Often referred to as deep sleep or slow wave sleep, stage 3 sleep is highly restorative, supporting the body’s ability to heal, grow and fight infection, among other processes.
Stage REM. During rapid eye movement (REM) sleep, brain activity increases and you may have vivid dreams. This stage of sleep may help boost creativity and cognition (your ability to think and remember).
Should you be concerned if your device says you aren’t getting enough of a particular stage of sleep?
Again, it’s more about how you feel and less about the numbers.
“The amount of time we spend in each sleep stage varies across the lifespan,” Dr. Mebust says. “The older we get, the less and less time we will spend in deep sleep. If you’re getting seven to eight hours of sleep a night, but still waking up tired, then that may be a warning sign that something is going on.”
Some medications can also affect how much time you spend in particular sleep stages. For example, Dr. Mebust shares that some antidepressants can decrease the amount of time you spend in REM sleep.
Late night eating eats into good quality rest
Frequent late-night meals can cause your sleep quality to take a dive. Why?
“When people eat and then lay down soon afterward, they can experience acid reflux or heartburn,” Dr. Mebust says. “Sometimes it causes them to wake up and choke, but sometimes it’s silent and they don’t even know it’s happening. Many people with sleep apnea also experience acid reflux.”
Eating frequent meals before bedtime can also lead to weight gain due to excess calories.
Why heart rate variability matters
Our heart rate fluctuates, or changes, while we sleep, and many sleep-tracking devices monitor these changes. Heart rate variability (HRV) measures the amount of time between two different heartbeats.
But why does our heart rate change?
The nervous system is constantly communicating with the heart and telling it whether to speed up or slow down depending on what the body needs, even when we sleep and throughout different stages of sleep.
“Heart rate variability is an indicator of resilience and how well the body can respond to changes,” says Dr. Mebust. “You want to have a high heart rate variability rather than a low heart rate variability. A low HRV is associated with increased risk of cardiovascular problems. People with sleep disorders like insomnia or sleep apnea also tend to have a decreased HRV.”
But just what that HRV number should be is difficult to pin down.
“Heart rate variability is unique to each person and depends on several factors like your age, emotional state, how hydrated you are, how well you have been sleeping and more,” Dr. Mebust says. “Use yourself as your own gold standard — if you start to see consistent dips in your HRV, then you may want to talk to your doctor.”
Are you getting enough oxygen?
While you catch 40 winks, your device may track your blood oxygen saturation — the average amount of oxygen in your bloodstream. Many things can influence your blood oxygen saturation, such as whether you have a cold and even the altitude at which you live.
But, like HRV, this is a metric worth paying attention to.
“If your blood oxygen levels are consistently dipping below 90 percent, you should consult your doctor,” Dr. Mebust says. “It can be a sign of a sleep disorder called sleep apnea.”
Sleep apnea occurs when a person experiences frequent disruptions to their breathing while they sleep. Many people don’t fully wake up when this happens, but may often feel fatigued throughout the day or experience other symptoms such as morning headaches.
Left untreated, sleep apnea can lead to chronic exhaustion and increase the risk of heart attack or stroke.
Is it taking you too long to fall asleep?
Sleep latency refers to how long it takes you to fall asleep. When should you be concerned about this metric?
“It can take up to 30 minutes for people to fall asleep,” Dr. Mebust says. “If it’s consistently taking longer than that, then you could be suffering from a sleep disorder like insomnia or restless legs syndrome, so it’s worth bringing up to your doctor.”
Caffeine could also be a culprit. Ingesting too much caffeine or having caffeine too close to bedtime can interfere with your ability to fall asleep and stay asleep. Caffeine’s effects can last up to seven hours, and it can take up to 24 hours for our bodies to fully process and eliminate caffeine, according to the Sleep Health Foundation.
In addition to caffeine, a poor-quality mattress and chronic pain can also make it difficult to routinely fall asleep within that 30-minute window.
When to see a doctor for sleep problems
We all have restless nights every now and then, but it’s a good idea to contact your primary care physician or a sleep specialist if you are consistently experiencing any of these symptoms:
- Excessive daytime sleepiness or fatigue
- Difficulty concentrating or remembering
- Inability to get enough sleep at night
- Frequently waking to urinate
- Loud snoring
- Gasping or choking during sleep
For children, behavior issues may be the biggest clue they have an underlying sleep problem or aren’t getting enough sleep.
“When children are experiencing behavioral problems, suddenly getting poor grades, having trouble regulating their emotions or unable to concentrate, it’s important to assess whether the underlying problem is a sleep disorder,” Dr. Mebust says.
