After transitioning to internship, physicians reported worse mood, shorter nightly sleep, and less physical activity. During internship, day-to-day changes in mood corresponded to fluctuations in physical activity and nightly sleep duration such that mood was highest when interns were physically active and well rested. Internship work schedules impacted timing of sleep and wake such that interns woke up, on average, substantially earlier during internship, which presaged reduced sleep duration and worsened mood. Though past studies have explored the consequences of problematic sleep, physical inactivity, and mood in this population, this investigation is the first to measure the association between changes in objectively measured sleep timing and duration and physical activity on daily mood during internship. Critically, our findings add to prior studies3, 4, 7, 10, 24 suggesting that long work hours, insufficient sleep, and circadian challenging shift schedules may create an insalubrious environment for intern mental health.
Our data confirm and extend to training physicians the bidirectional relationship between daily mood and sleep duration observed in prior subjective studies. We found that when interns obtained shorter sleep, they reported poorer mood the following day, which, in turn, presaged shorter sleep the next night. These results lend objective support to research linking insufficient sleep and negative mood in medical residents,10, 24 as well as to prior demonstration of reciprocity between daily mood and self-reported nightly sleep in non-resident populations.25, 26 It is notable that the influence of sleep on mood the next day in our study was substantially larger than the effect of daily mood on sleep the subsequent night. Given that interns experience significant sleep challenges and truncation due to long work hours and circadian misaligned shift schedules,3, 4, 7, 10, 23 these findings highlight the high risk for sleep-related mood perturbations in this population.
Indeed, our data offer critical insights into the effects of internship-related changes in sleep-wake timing and shift work on sleep duration and mood. After transitioning to internship, physicians woke up an average of 1 h and 30 min earlier than baseline. However, these earlier wake times during internship were not accompanied by corresponding changes in bedtimes. This finding suggests that insufficient sleep in this population is exacerbated by interns not adjusting or having difficulty adjusting their bedtime behaviors to accommodate work schedules enforcing earlier wake times. As the restriction of sleep leads to deterioration of neurocognitive functioning,27 trainees unable to adjust their sleep timing to their internship work schedules may be at risk for impaired neurocognitive function and medical errors. Moreover, we observed that drastic shifts in sleep timing characteristic of shift work led to reductions in sleep duration and mood. Importantly, these associations were found when intern sleep-wake timing was either earlier or later than pre-internship routine. However, stronger effects of misaligned sleep-wake timing on short sleep and negative mood were observed when intern sleep schedules were advanced rather than delayed, a finding that is especially concerning since intern midsleep was earlier than baseline patterns on 71.7% of nights during internship.
Evidence supporting the negative impact of circadian challenging work schedules on sleep and mood are consistent with data available from night and rotating shift workers.28, 29 Owing to high rates of rotating, night, and extended shift schedules, residents are at elevated risk for shift work disorder, a circadian rhythm sleep disorder.30, 31 Given the effects of sleepiness and fatigue on physician performance,8, 9, 32 shift work disorder in this at-risk population may represent an under-recognized threat to resident health and patient welfare.
Physical activity during residency is an understudied area that warrants greater attention for its role in regulating intern stress and psychological wellbeing. Consistent with cross-sectional research showing lower exercise rates for medical residents than medical students,6 our accelerometry-based estimates of daily steps demonstrated a > 10% decrease in average daily physical activity after transitioning to internship. As interns reported poorer mood when they were less active, this reduction in physical activity may increase risk for negative mood outcomes. These findings echo research highlighting the mood-improving effects of physical activity and exercise,33, 34 and support recommendations for programmatic efforts in medical education to promote physical activity and increase access to exercise facilities to combat sedentariness and improve stress reduction.11
The present study should be interpreted in light of certain limitations. First, our sample comprised of 33 physicians in the internship program at the University of Michigan Medical School only; thus, rates of short sleep, physical activity, and other key factors should not be interpreted as prevalence rates for the overall intern population. While our large number of observations provides statistical power to assess within-subjects effects, the limited number of subjects assessed limits the statistical power to detect between-subjects effects. Further, because the mixed models utilized just 33 observations for pre-internship factors (i.e., the number of subjects in the study), overfitting of between-subjects effects may have occurred, although the consistence of these findings with the extant literature may temper this concern. In addition, only data from pre-internship until December 31st were collected. Future investigations may benefit from continuous data collection throughout the entire intern year, which will provide insights into any potential changes in these relationships across the second half of internship. Further, it is unclear what, if any, effect self-monitoring may have had on interns’ impressions of their mood, sleep, or physical activity and how this self-monitoring may have influenced intern behaviors. Though accelerometry-based sleep monitors exhibit good sensitivity for detecting sleep, they suffer from poor specificity and have been shown to overestimate sleep duration.15, 16, 35 Therefore, our data likely overestimate nightly sleep duration in this population. Future studies on nightly sleep in interns would benefit from sleep data collection using both subjective (e.g., sleep diaries) and objective (e.g., accelerometry or actigraphy) measures, as well as pre-internship assessment of circadian typology such as self-reported diurnal preference. Daily reports of shift schedules would improve future exploration of work hours and shift timing on intern health behaviors and outcomes. Lastly, although Mood 24/7 has shown promise in mobile mood monitoring,18 its use in research is limited and research on its clinical utility would benefit research using such prospective mobile data.
In summary, our findings suggest that interventions to increase sleep opportunity and physical activity may improve intern mood in this depression-vulnerable population. Physicians should be educated before internship on the importance of entraining their sleep-wake routines to earlier work schedules common to residency, and introduced to techniques to rapidly resynchronize their circadian rhythms when scheduled for early morning, night, or rotating shift work.36,37,–38 Future research is needed to evaluate whether restructuring work schedules to best align with resident sleep-wake timing to permit interns to awaken close to their natural wake times, and designing shift changes to allow for adequate time for circadian resynchronization may improve both intern sleep and mood, and may protect against shift work disorder and reduce intern drowsiness.