Limiting first-year medical residents to 16-hour work shifts, compared to “flexing” them to allow for some longer shifts, generally makes residents more satisfied with their training and work-life balance, but their training directors more dissatisfied with curtailed educational opportunities. That’s one conclusion of a new study published online March 20 in the New England Journal of Medicine.

For the study, part of a 5-year effort funded by the National Heart, Lung, and Blood Institute and the Accreditation Council for Graduate Medical Education (ACGME) and led by the Perelman School of Medicine at the University of Pennsylvania in in close collaboration with The Johns Hopkins University, the investigators surveyed and tracked the activities of thousands of first-year residents—or interns—in 63 internal medicine training programs nationwide. The findings also found that shift-length regulations have no impact on interns’ activity or test of medical knowledge scores one way or the other.

“The effects of limiting trainee duty hours were not known,” says Sanjay Desai, MD, associate professor of medicine and director of the Osler Medical Training Program at the Johns Hopkins University School of Medicine. “A randomized trial with many institutions and generalizable findings was needed to inform the issue,” he adds.

Until the early 2000s, training program guidelines and regulations generally had no limits on shift lengths for doctors-in-training, leading many residents to work upwards of 90 hours a week, with shifts as long as 36 hours. Training directors often justified the long hours as a way to prepare physicians for a lifetime of learning and treating patients successfully under pressure and often with little sleep. They also pointed to the need for continuity of care, made more difficult by frequent shift changes.

In 2003, however, the ACGME first set regulations based on expert opinion—30-hour maximum shifts and 80-hour maximum workweeks—for all accredited residency programs in the US.

Despite a series of observational studies that showed no difference in the quality of patient care with those stricter limits, even more stringent regulations were put forward in 2011—limiting interns to 16-hour shifts and more senior residents to 28-hour shifts. These new limits increased controversy, with many training directors arguing that junior clinicians needed to follow patients for longer continuous periods to really learn how to care for them.

“Many educators have worried that the shift work created by limited duty hours will undermine the training and socialization of young physicians,” says the study’s principal investigator David Asch, MD, John Morgan Professor of Medicine at the Perelman School of Medicine at the University of Pennsylvania. “Educating young physicians is critically important to health care, but it isn’t the only thing that matters. We didn’t find important differences in education outcomes, but we still await results about the sleep interns receive and the safety of patients under their care.”

The researchers note that while advocates for duty hour limits have worried that long shifts can lead to fatigue and fatigue can cause errors, short shifts mean more handoffs of care and handoffs can also cause errors. “We created this study to simultaneously evaluate the effect of alternative duty hour policies on resident education, resident sleep and alertness, and patient safety. The part of this study being reported in the March 20 issue of the New England Journal of Medicine is about medical education. It will be essential to see the rest of the data before we know where to go next,” says Asch. He expects those results to be available by early 2019.