A higher percentage of those who worked more hours had scores high enough to qualify for a diagnosis of moderate to severe depression—serious enough to warrant treatment—compared to those who worked fewer hours. The research team used advanced statistical methods to simulate a randomized clinical trial, which took into account many other factors in the doctor’s personal and professional life. The results show a “dose response” effect between working hours and symptoms of depression. There was an average increase in symptoms of 1.8 points on a standardized scale for those working 40 to 45 hours, ranging up to 5.2 points for those working more than 90 hours.
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The team concluded that of all the stressors that adversely affect doctors, working long hours is a major contributor to depression. The University of Michigan team studied 11 years of data on more than 17,000 first-year doctors. The recently graduated doctors were in training at hundreds of hospitals across the United States. The data comes from the Intern Health Study, which annually recruits new medical school graduates to take part in a 12-month examination of their depression symptoms, work hours, sleep and more as they complete their first year of residency. The most common work hour levels were between 65 and 80 hours per week for the doctors in the study.