Effects of Sleep, Physical Activity, and Shift Work on Daily Mood: a Prospective Mobile Monitoring Study of Medical Interns

Background: Although short sleep, shift work, and physical inactivity are endemic to residency, a lack of objective, real-time information has limited our understanding of how these problems impact physician mental health. Objective: To understand how the residency experience affects sleep, physical activity, and mood, and to understand the directional relationships among these variables. Design: A prospective longitudinal study. Subjects: Thirty-three first-year residents (interns) provided data from 2 months pre-internship through the first 6 months of internship. Main Measures: Objective real-time assessment of daily sleep and physical activity was assessed through accelerometry-based wearable devices. Mood scaled from 1 to 10 was recorded daily using SMS technology. Average compliance rates prior to internship for mood, sleep, and physical activity were 77.4, 80.2, and 93.7%, and were 78.8, 53.0, and 79.9% during internship. Key Results: After beginning residency, interns lost an average of 2 h and 48 min of sleep per week (t = − 3.04, p <.01). Mood and physical activity decreased by 7.5% (t = − 3.67, p <.01) and 11.5% (t = − 3.15, p <.01), respectively. A bidirectional relationship emerged between sleep and mood during internship wherein short sleep augured worse mood the next day (b =.12, p <.001), which, in turn, presaged shorter sleep the next night (b =.06, p =.03). Importantly, the effect of short sleep on mood was twice as large as mood’s effect on sleep. Lastly, substantial shifts in sleep timing during internship (sleeping ≥ 3 h earlier or later than pre-internship patterns) led to shorter sleep (earlier: b = −.36, p <.01; later: b = − 1.75, p <.001) and poorer mood (earlier: b = −.41, p <.001; later: b = −.41, p <.001). Conclusions: Shift work, short sleep, and physical inactivity confer a challenging environment for physician mental health. Efforts to increase sleep opportunity through designing shift schedules to allow for adequate opportunity to resynchronize the circadian system and improving exercise compatibility of the work environment may improve mood in this depression-vulnerable population.