While sleep trackers offer insights into sleep duration and schedule consistency for many users, new research indicates these devices may not accurately reflect a person's actual sleep quality.
According to a review of studies, the data collected by wearables often does not align with how individuals feel about their sleep. This discrepancy could lead to a false impression of sleep health and potentially delay necessary diagnoses and treatments for conditions like insomnia. The findings suggest that the measurements captured by these devices account for only a small fraction of the variation in perceived sleep quality.
One study examined in the review compared data from Fitbit devices with polysomnography (PSG), a comprehensive sleep study that measures brain waves, heart rate, breathing, blood oxygen, and body movements. Among healthy sleepers, Fitbit data showed acceptable agreement with PSG for a majority of participants. However, this agreement significantly decreased among individuals with insomnia, as well as in older adults and those with other health conditions.
Researchers propose that trackers might misinterpret periods of lying still while awake as continued sleep. This could lead to an overestimation of actual sleep time and sleep efficiency, potentially providing misleading information to users. The authors of the review noted that such inaccuracies could discourage individuals experiencing persistent sleep problems from seeking medical attention if their tracker indicates they are sleeping adequately.
Despite these limitations, the review's authors emphasize that sleep trackers can still offer valuable information regarding sleep duration and regularity. However, they advise against relying solely on device data. Experts recommend complementing tracker data with a sleep diary, where individuals can record how rested they feel and note instances of waking during the night. This combined approach can provide a more complete understanding of sleep health.