An irregular sleep schedule can increase a person’s risk of depression over the long term as much as getting fewer hours of sleep overall, or staying up late most nights, a new study suggests.
Even when it comes to just their mood the next day, people whose waking time varies from day to day may find themselves in as much of a foul mood as those who stayed up extra late the night before, or got up extra early that morning, the study shows.
The study is based on data gathered by tracking sleep and other activity of first year medical interns through commercial devices worn on their wrists, and asking them to report their daily mood on a smartphone app and take quarterly tests for signs of depression.
Those whose devices showed they had variable sleep schedules were more likely to score higher on standardized depression symptom questionnaires, and to have lower daily mood ratings. Those who regularly stayed up late, or got the fewest hours of sleep, also scored higher on depression symptoms and lower on daily mood. The findings add to what’s already known about the association between sleep, daily mood and long-term risk of depression. They highlight sleep consistency as an underappreciated factor to target in depression and wellness.
Wearable devices that estimate sleep are now being used by millions of people, including the Fitbit devices used in the study, other activity trackers and smart watches. These devices, for the first time, allow us to record sleep over extensive time periods without effort on behalf of the user. There are still questions surrounding the accuracy of the sleep predictions consumer trackers make, though initial work suggests similar performance to clinical and research grade actigraphy devices which are cleared by the FDA.
The team notes that the relatively young group of people in the study – with an average age of 27, and holding both college and medical degrees – are not representative of the broader population. However, because all of them experience similar workloads and schedules, they are a good group to test hypotheses in. The researchers hope that other groups will study other populations using similar devices and approaches, to see if the findings about variation in sleep schedule hold up for them.