The study of sleep using wearable smart devices has advanced significantly over the past five years, with companies such as Apple and Samsung making notable progress in using smartwatches and smart rings to track sleep patterns.
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These devices no longer merely record how many hours a person sleeps daily. They now provide detailed analysis of the different sleep stages, including deep sleep and rapid eye movement (REM) sleep.
A large study by researchers from the University of California, San Francisco and the University of California, San Diego suggests that wearable devices may also provide important indicators of mental health.
The study found an association between irregular sleep and wake times and increased severity of symptoms of depression, anxiety and loneliness.
While previous studies have focused mainly on sleep quality and the number of hours slept, the link between keeping regular sleep times and mental health has not received the same amount of research.
In a paper published in the journal Scientific Reports, the researchers explained that commercially available wearable devices linked to smartphone apps can collect data on sleep regularity and offer recommendations based on that data to improve users' habits, such as identifying the ideal times to go to bed and wake up.
A study of more than 23,000 people
The researchers collected sleep data from more than 23,000 participants, each of whom provided data covering an average of 154 days. The participants had an average age of 46.
All participants wore smart rings that recorded sleep and wake times, using biosensors and the movement data the devices captured.
The researchers used this information to calculate a Sleep Regularity Index (SRI), with scores ranging from zero to 100. A higher score indicates a more regular sleep pattern.
Participants also completed monthly questionnaires assessing their levels of loneliness, anxiety and depression.
The results showed that people with greater irregularity in their sleep times generally reported higher levels of depression and anxiety symptoms.
The average sleep regularity index among participants who showed no symptoms of depression, or only very minimal ones, was about 84 points.
By contrast, the index fell to 83 points among those with mild depression symptoms, 81 among those with moderate symptoms, and down to 75 among participants who reported severe depression symptoms.
In practical terms, a score of 84 on the sleep regularity index means that sleep and wake times vary by about one hour from day to day, while a score of 75 indicates variations approaching an hour and a half.
Irregular sleep linked to more anxiety and loneliness
The study found similar results when it analysed the relationship between sleep regularity and levels of anxiety.
An average sleep regularity index of 84 points was associated with normal levels of anxiety, while the average fell to 79 points among participants with severe anxiety symptoms.
A similar pattern emerged when the researchers examined the link between sleep and wake regularity and feelings of loneliness.
The researchers noted that the relationship between disrupted sleep cycles and mental health problems may run in both directions. Irregular sleep may be one symptom of deteriorating mental health, while other research suggests that sleep disruption may come before these problems and contribute to their development.
In other words, it remains unclear whether irregular sleep timing causes an increase in psychological symptoms or results from them, or whether the relationship runs in both directions.
How can smart watches and rings help?
The researchers believe that keeping to a regular sleep schedule may be a useful step, but the study did not test whether improving sleep regularity actually eases symptoms of depression or anxiety.
They stressed that this question requires further research.
Modern smart devices offer tools that may help users organise their sleep. Their functions go beyond tracking sleep cycles: they also allow users to set schedules and create alerts that remind them of their bedtimes.
The apps linked to these devices also provide detailed reports on sleep patterns, including the actual number of hours slept, average time taken to fall asleep, sleep quality, and changes in sleep timing.
The researchers said that, taken together, the findings point to a significant association between sleep regularity and mental health, based on data collected automatically in everyday life using commercially available wearable devices.
They added that the results are consistent with earlier research showing that improving sleep quality may contribute to better mental health.
The research team stressed that sleep regularity is an indicator that can be measured easily using widely available technology, which gives the findings clinical and public health relevance, particularly as individuals can understand their sleep patterns and work to adjust them.
Technology that goes beyond sleep monitoring
Some smartwatches from Apple and Samsung can do more than record sleep times. They can also detect signs that may point to sleep apnoea, a health condition that affects breathing during the night.
These capabilities may make wearable devices useful tools for tracking healthy habits and identifying changes that may warrant attention.
The report stresses, however, that people experiencing symptoms of anxiety or depression should consult a qualified healthcare professional for proper assessment and help.
Where such symptoms are linked to sleep disorders, smart devices can play a supportive role by monitoring sleep patterns and helping users assess their daily habits.
Overall, the study suggests that regular sleep and wake times may be an important indicator of mental health, alongside the number of hours slept and sleep quality. However, proving that adjusting these times eases symptoms of depression and anxiety will require further studies.
