Irregular sleep does more than just make you grouchy. When it comes to causing depression, erratic sleep can be as detrimental as too-little sleep.

University of Michigan researchers tracked sleep and mood data from about 2,100 first-year physicians using activity monitors, mood-measuring phone apps and quarterly depression tests.

The study focused on young doctors because they typically work long, intense days and irregular hours. Two weeks of data were collected before the doctors started their internships and there was an average of four months of monitoring during their internship year. That allowed the researchers to measure the effect of changes in sleep pattern and duration.

Those doctors who had variable sleep schedules were more likely to have higher scores on standardized depression tests. Staying up late and getting less sleep also resulted in higher depression scores and lower mood ratings.

While young doctors may not be representative of the population as a whole, the research methods may be easily adaptable to other groups of people. Millions of people already wear activity-tracking devices, creating the possibility that sleep habits could be recorded over long time periods with almost no effort by the users.

One goal is to develop ways people at risk for depression can self-manage their sleep habits. Employers could also use the information to develop optimal work schedule.

When it comes to a good night’s sleep, think of it as you would a movie or compelling book or even a sporting event. If you only get it in bits and pieces, you’ll miss out on all the fulfilment and come away grumpy. And nobody wants that.