A retail employee wheels out a rack of girls’ clothing in Phoenix.

Working too few hours to make ends meet. Scrambling to arrange childcare around a schedule that is constantly shifting. Commuting to work only to be sent home without pay. These are some of the big hurdles confronting millions of workers in the U.S. retail and service sectors as they seek to build stable livelihoods. Increasingly, more and more employers are using scheduling systems that match the number of workers on the job with predicted consumer demand, which often wreak havoc on workers who have little control over a schedule that changes at a moment’s notice.

The consequences of unpredictable schedules have been well-documented by the media and researchers alike, and many accounts have suggested that these kind of worker schedules may have consequences for health as well. Now, a new working paper from Equitable Growth by sociologists Daniel Schneider of the University of California-Berkeley and Kristen Harknett at the University of Pennsylvania looks specifically at the health and well-being of workers who work unpredictable and variable hours. The results are overwhelmingly negative, with the variability of work hours being strongly associated with a host of physical and mental health issues as well as financial instability.

The researchers use data collected from a national sample of hourly retail workers at eight brick-and-morter companies, all of which are among the largest 15 retail employers in the United States. The two sociologists zero in on the correlation between the health and well-being of workers and three scheduling practices that many of these workers experience— volatility in work hours from week to week, variation in the times of workers’ shifts, and little advance notice for upcoming work schedules.

Somewhat unsurprisingly, the authors find that those workers with greater variation in their weekly work hours were significantly more likely to prefer more work hours compared to those who had set shifts. Schneider and Harknett also find that unstable and unpredictable work schedules are negatively associated with household financial insecurity, even when controlling for hourly wage and overall household income. That’s because workers’ pay fluctuates from week to week depending on how many hours they are given, which affects everything from the ability to put food on the table to engaging in any long-term financial planning.

The stress of these schedules takes a toll. Schneider and Harknett found that those who work a variable schedule are much less likely to have good quality sleep and are more likely to report “serious psychological distress.” Those with volatile schedules also spend less time with their children and are more stressed out. If sustained, research shows that parental stress can harm kids’ mental and physical health, which has lasting effects into adulthood.

The authors point out that, importantly, it is the variability of hours rather than nonstandard timing of work that has the most significant association with harmful outcomes (excluding those who work a regular night shift). But they do find that having at least two-weeks notice of their next work schedules makes a significant difference in terms of a workers’ well-being. As the authors say, this advance notice seems likely “to improve workers’ ability to plan their child care, to combine work with schooling or a second job, and in turn may reduce stress and improve mental health.”

Many state and local governments (including Washington, D.C. and Seattle) are currently debating legislation that would require two-weeks advance notice of schedules and access to more work hours. This research adds to the growing body of work documenting the harm these scheduling practices inflict onto workers.