Irregular sleep schedules can affect mood and risk of developing symptoms of depression according to a study of first-year medical residents that used Fitbits and smartphones.

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

The interns, as they are called in their first year of residency training after medical school, all experienced the long intense work days and irregular work schedules that are the hallmark of this time in medical training. Those factors, changing from day to day, altered their ability to have regular sleep schedules.

The new paper is based on data gathered by tracking the interns’ sleep and other activity 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.

Story Source:
Materials provided by Michigan Medicine — University of Michigan. Original written by Kara Gavin. Note: Content may be edited for style and length.