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ANN ARBOR, Mich. — The more hours people work each week in a stressful job, the greater their risk of depression rises, according to a new study examining doctors.

Researchers from Michigan Medicine found that those working 90 or more hours a week saw changes in depression scores that were three times higher than the change in depression symptoms among those working 40 to 45 hours a week.

A higher percentage of those who worked a larger number of hours had scores high enough to qualify for a diagnosis of moderate to severe depression — serious enough to warrant treatment compared with those working fewer hours. The research team used advanced statistical methods to simulate a randomized clinical trial, which accounted for many other factors in a doctor’s personal and professional lives.

Results show a “dose response” effect between hours worked and symptoms of depression. There was an average symptom increase of 1.8 points on a standard scale for those working 40 to 45 hours, ranging up to 5.2 points for those working more than 90 hours.

The team concludes that, among all the stressors negatively affecting doctors, working a large number of hours is a major contributor to depression. The University of Michigan team studied 11 years’ worth of data on more than 17,000 first-year medical residents. The recently graduated doctors were in training at hundreds of hospitals across the United States.

The data comes from the Intern Health Study, which recruits new medical school graduates each year to take part in a 12-month examination of their depressive symptoms, work hours, sleep, and more while they complete the first year of residency, also called the intern year. The most common work hour levels were between 65 to 80 hours per week for the doctors in the study.

It’s easier to deal with stress ‘when you have more time to recover’

The Accreditation Council for Graduate Medical Education, which sets national standards in the U.S. for residency programs, currently sets an 80-hour limit on residents’ work weeks, but that can also be an average across four weeks and there are possible exceptions. ACGME also limits the length of a single shift and the number of days in a row that residents work.

However, the research team says their findings point to a clear need to further reduce the number of hours doctors work each week.

“This analysis suggests strongly that reducing the average number of work hours would make a difference in the degree to which interns’ depressive symptoms increase over time, and reduce the number who develop diagnosable depression,” says Amy Bohnert, Ph.D., the study’s senior author and a professor at the U-M Medical School, in a media release. “The key thing is to have people work fewer hours; you can more effectively deal with the stresses or frustrations of your job when you have more time to recover.”

1 in 3 doctors in training made a medical error

Study lead author Yu Fang, noted that the number of hours doctors work is important, but so are the training opportunities that come from time spent in hospitals and clinics.

“It is important to use the time spent at work for supervised learning opportunities, and not low-value clinical service tasks,” Fang says.

Intern Health Study founder Professor Srijan Sen adds new physicians entering the most stressful year of their careers make a “perfect group” in which to study the role of many factors in the risk or onset of depression.

“We would expect that the negative effect of long work hours on physician mental health would be present in other professions,” says Prof. Sen.

The average age of the doctors in the study was 27, and just over half were women. Less than one in 20 met the criteria for moderate to severe depression at the start of intern year. In all, 46 percent had a stressful life event such as a family death or birth, or getting married, during their intern year. Meanwhile, 37 percent reported that they had been involved in at least one medical error during the year.

“This paper demonstrates how big of an impact that the single factor of work hours has on clinician depression and well-being,” Prof. Sen concludes.

The findings are published in the New England Journal of Medicine.

South West News Service writer Stephen Beech contributed to this report.

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