Irregular sleep schedules linked to moodiness and depression, study shows

An irregular sleep program can increase a person’s risk of depression in the long run as much as sleeping less hours overall or staying up late most nights, a new study suggests.

Even when it comes only to your mood the next day, people whose waking time varies from day to day may find themselves in as much a bad mood as those who stayed up late the night before or woke up very early that morning, study shows.

The study, conducted by a team from Michigan Medicine, the academic medical center at the University of Michigan, uses data from direct measurements of sleep and mood from more than 2,100 early-year physicians over a year. It is published in npj Digital Medicine.

Inmates, as they are called in the first year of medical residency after medical school, experienced the long and intense working hours and irregular working hours that characterize this period in medical training. These factors, changing from day to day, altered your ability to have regular sleep schedules.

The new article is based on data collected by monitoring inmates’ sleep and other activities using commercial devices worn on their wrists and asking them to report their daily mood on a smartphone app and take quarterly tests to detect signs of depression.

Those whose devices were shown to have varying sleep times were more likely to score higher on standardized depression symptom questionnaires and to have lower daily mood assessments. Those who regularly stayed up late, or slept less hours, also scored more on symptoms of depression and less on daily mood. The findings add to what is already known about the association between sleep, daily mood and long-term risk of depression.

“Advanced wearable technology allows us to study the behavioral and physiological factors of mental health, including sleep, on a much larger scale and more accurately than before, opening up an exciting field for us to explore,” said Yu Fang, MSE, lead author of the new article and research specialist at the Michigan Neuroscience Institute. “Our findings are aimed not only at guiding self-management on sleep habits, but also at informing institutional programming structures.”

Fang has been a member of the Intern Health Study team, led by Srijan Sen, MD, Ph.D., who has been studying the mood and risk of depression in first-year medical residents for more than a decade. The study collected an average of two weeks of data prior to the beginning of the doctors’ hospitalization years and an average of almost four months of monitoring during the year of hospitalization.

For the new article, the team worked with Cathy Goldstein, MD, MS, associate professor of neurology and physician at the Sleep Disorders Center at Michigan Medicine.

She notes that 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 for long periods of time without effort on the part of the user,” says Goldstein. “We still have doubts about the accuracy of the sleep predictions that consumer trackers make, although the initial work suggests a performance similar to the clinical grade and research actigraphy devices that are released by the FDA.”

Sen, who holds the Eisenberg chair in Depression and Neuroscience and is a professor of neuroscience and psychiatry, notes that the new findings are based on what his team’s work has already shown about the high risk of depression among new doctors and other associated underlying factors with a high risk.

“These findings highlight the consistency of sleep as an underestimated factor in achieving depression and well-being,” he says. “The work also highlights the potential of wearable devices in understanding important constructs relevant to health that we previously could not study at scale.”

The team notes that the relatively young group of people in the study – with an average age of 27 and graduated in medicine and college – is not representative of the general population. However, as they all experience similar workloads and schedules, they are a good group for testing hypotheses. The researchers hope that other groups will study other populations using similar devices and approaches, to see if the findings about the variation in the sleep schedule hold for them.

Fang, for example, notes that parents of young children can be another important group to study. “I also wish my 1 year old son could learn about these discoveries and just wake me up at 8:21 am every day,” she jokes.