The introduction of wearable technologies has sparked a fascination with personal metrics, particularly when it comes to sleep analysis. Those who have trouble sleeping may think this data could help them sleep however, recent assessments have suggested otherwise.
“These sleep wearables should be used cautiously to avoid misleading conclusions about sleep stages,” says Stanford Lifestyle Medicine sleep expert, Jamie Zeitzer, PhD. “Even if these metrics were accurate, which they aren’t, how much do they matter?”
Dr. Zeitzer says it is crucial to not get too focused on the feedback that wearables provide. “A device’s perception of our sleep quality can greatly influence our own,” says Dr. Zeitzer. “For instance, a device indicating a ‘bad night’s sleep’ can create a perception of fatigue, even if the individual slept soundly. This misperception can lead to feelings of tiredness or even induce insomnia.”
The Importance of REM Sleep
While wearables gather data on all the stages our brain goes through during sleep, one particular sleep stage of interest is rapid-eye movement (REM) sleep due to its positive effects on brain development and learning, regulating emotions and consolidating memories.
During REM sleep, our brain activity is similar to that of being awake and it is during this stage when most of our dreams occur. Research suggests that getting enough REM sleep may help mitigate potentially negative emotional reactions during the day since REM sleep is associated with a reduction in amygdala reactivity—the area of the brain responsible for anxiety, stress, and fear.
On average, REM sleep constitutes about 20 to 25 percent of our total sleep time. This means that getting 7 to 8 hours of sleep would equal around 90 minutes of REM sleep. The REM stage usually starts 90 minutes after you fall asleep, with each of your REM cycles getting longer throughout the night: the first period typically lasts 10 minutes, with the final one lasting up to an hour. Therefore, because REM increases with each cycle, if you do not sleep for long enough, your body may not get enough REM sleep to feel rested the next morning.
“If you need eight hours of sleep, but only sleep for six hours, not only is that a 25 percent reduction in total sleep, that may translate to 60 or 90 percent of lost REM sleep,” says Dr. Zeitzer.
The Importance of Sleep Timing
Rather than looking at a wearable device to determine whether we’ve gotten enough sleep, Dr. Zeitzer suggests checking in with ourselves and assessing our fatigue levels.
“Wearables can be misleading, so a better way to assess whether we’ve gotten enough REM sleep, is to see if there are any functional consequences, such as feeling tired or having reduced mental clarity,” says Dr. Zeitzer.
Instead of focusing on the REM sleep data provided by your wearable, Dr. Zeitzer suggests focusing on sleep timing, i.e. going to bed and waking up at the same time every day. “Quality sleep is highly dependent on consistency in sleep timing,” he says. “Consistent sleep-wake times can keep your circadian rhythm in check, to ensure you get enough quality sleep.”