Apps and fitness trackers that measure sleep: Are they useful?

ARE THE MEASURES VALID?

Only a few studies have examined the validity and accuracy of current fitness trackers and apps for measuring sleep.

The available studies are difficult to compare; most have been small and used different actigraphy devices for comparison. Some tested healthy volunteers, others included people with suspected or confirmed sleep disorders, and some had both types of participants. In many studies, the device was compared with polysomnography for only 1 night, making the “first-night effect” likely to be a confounding factor, as people tend to sleep worse during the first night of testing. Technical failures for the devices were noted in some studies.¹² In addition, some currently used apps may use different platforms than the devices used in these studies, limiting the extrapolation of results.

Two fitness tracking devices (Fitbit^13,14  and Jawbone UP^15–17) were compared with polysomnography and actigraphy in several studies in children and adults (Table 1). The devices tended to overestimate sleeping time, sleep efficiency, and latency to sleep onset and underestimate awake time after falling asleep. Some studies noted that differences were more pronounced for those with the most disturbed sleep.

As with fitness trackers, few studies have been done to examine the validity of smartphone apps.⁵ Findings of 3 studies are summarized in Table 2.^17–19 In addition to tracking the duration and depth of sleep, some apps purport to detect snoring, sleep apnea, and periodic limb movements of sleep. Discussion of these apps is beyond the scope of this review.

In general, sleep tracking devices are fair to good at detecting sleep but poor at determining wakefulness. They are inaccurate for determining absolute sleep parameters (ie, total sleep time, sleep efficiency, wake time after sleep onset, and sleep onset latency) and in distinguishing the different sleep stages compared to polysomnography. Age-related differences have been found between consumer sleep devices compared with polysomnography and actigraphy-derived measures; because adults are likelier to lie still when awake, activity monitors are prone to overestimate sleep time in adults. Comparisons in patients with sleep apnea are conflicting.^12,15 Claims that the “sensitive” mode may be appropriate for users with sleep disorders are thus far unsubstantiated.

ARE THE DEVICES CLINICALLY USEFUL?

Although a thorough history remains the cornerstone of a good evaluation of sleep problems, testing is sometimes essential, and in certain situations, objective data can complement the history and clarify the diagnosis.

Polysomnography remains the gold standard for telling when the patient is asleep vs awake, diagnosing sleep-disordered breathing, detecting periodic limb movements and parasomnias, and aiding in the diagnosis of narcolepsy.

Actigraphy, which uses technology similar to fitness trackers, can help distinguish sleep from wakefulness, reveal erratic sleep schedules, and help diagnose circadian rhythm sleep disorders. In patients with insomnia, actigraphy can help determine daily sleep patterns and response to treatment.²⁰ It can be especially useful for patients who cannot provide a clear history, eg, children and those with developmental disabilities or cognitive dysfunction.

Consumer sleep tracking devices, like actigraphy, are portable and unobtrusive, providing a way to measure sleep duration and demonstrate sleep patterns in a patient’s natural environment. Being more accessible, cheaper, and less time-consuming than clinical tests, the commercially available devices could be clinically useful in some situations, eg, for monitoring overall sleep patterns to look for circadian sleep-wake disorders, commonly seen in shift workers (shift work disorder) or adolescents (delayed sleep-wake phase disorder); or in patients with poor motivation to maintain a sleep diary. Because of their poor performance in clinical trials, they should not be relied upon to distinguish sleep from wakefulness, quantify the amount of sleep, determine sleep stages, and awaken patients exclusively from light sleep.

Discerning poor sleep hygiene from insomnia

Patients with insomnia tend to take longer to go to sleep (have longer sleep latencies), wake up more (have more disturbed sleep with increased awakenings), and have shorter sleep times with reduced sleep efficiencies.²¹ Sleep tracking devices tend to be less accurate for patients with short sleep duration and disturbed sleep, limiting their usefulness in this group. Furthermore, patients with insomnia tend to underestimate their sleep time and overestimate sleep latency; some devices also tend to overestimate the time to fall asleep, reinforcing this common error made by patients.^22,23

On the other hand, data from sleep tracking devices could help distinguish poor sleep hygiene from an insomnia disorder. For example, the data may indicate that a patient has poor sleep habits, such as taking long daytime naps or having significantly variable time in and out of bed from day to day. The total times asleep and awake in the middle of the night may also be substantially different on each night, which would also possibly indicate poor sleep hygiene.