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Association between mental healthand duty hours of postgraduate
residents in Japan: a nationwide
cross‑sectional study
Kazuya Nagasaki1, Yuji Nishizaki2, Tomohiro Shinozaki3, Taro Shimizu4, Yu Yamamoto5,
Kiyoshi Shikino6, Sho Fukui7, Sho Nishiguchi8, Masaru Kurihara9, Koshi Kataoka2,
Yasuharu Tokuda10 & Hiroyuki Kobayashi1*
The new duty hour (DH) limit for doctors in Japan will begin in 2024, setting the maximum DHs forpostgraduate residents at approximately 80 h weekly. To set appropriate limits, understanding theassociation between DHs and psychological health is necessary. Thus, we assessed the relationshipbetween residents’ psychological health and DHs. We conducted a cross-sectional study involving
examinees of the General Medicine In-training Examination 2020. Mental health outcomes were
measured dichotomously using the Patient Health Questionnaire-2 for depression and Mini-Z 2.0, forburnout, stress, and satisfaction. Weekly DHs were measured in seven categories at 10-h intervals.
The prevalence ratios (PRs) between the DH categories were estimated for each outcome. Of the 6045
residents who provided data on DHs and psychological outcomes, 37.3% showed signs of depression,
21.6% experienced burn out, and 39.2% were highly stressed. In contrast, 62.3% were highly
satisfied with their training. Proportions of burnout were higher among residents in Category 6 (≥ 90
and < 100 h; PR 1.36; 95% CI 1.11–1.66) and Category 7 (≥ 100 h; PR 1.36; 95% CI 1.10–1.68) comparedwith residents in Category 3 (≥ 60 and < 70 h; reference). The results partially support the weekly 80-h
DH limit in terms of resident well-being.
Excessive working hours are a long-standing social problem in Japan, causing health problems such as depression,suicide, and karoshi (occupational sudden death)1. Doctors work particularly long hours, especially postgraduate
residents and junior doctors. According to a 2018 survey by the Ministry of Health, Labor and Welfare (MHLW),
10% of all doctors work > 80 h weekly; moreover, doctors in their 20 s (mostly residents) have the longest average
working hours at 76.1 h ­weekly2. The need for resident duty hour (DH) restriction led to a gradual decrease inwork hours in Europe, the United States, Canada, and other ­regions3. The primary motivations for limiting DHsvary from region to region and include medical safety, human rights, and well-being.
In Japan, restrictions on residents’ DHs have been discussed from the perspective of worker well-being. The
government set a uniform upper limit on working hours (up to 720 h per year of overtime) for all workers starting in 2­ 0194. However, the MHLW argued for setting a different limit for doctors, to maintain the healthcare­system5. As a result, it was decided that the upper limit for doctors should be 960 h per year of overtime work(equivalent to a 60-h work week), to be implemented in 2024. However, two exceptions were made: medical
institutions that are important for maintaining community healthcare and resident doctors. Residents wereallowed to work up to 1860 h of overtime per year (equivalent to an 80-h work week) for educational purposes.
Members of the MHLW committee on work style reform thought that long DHs are required to maintain the1

Department of Internal Medicine, Mito Kyodo General Hospital, University of Tsukuba, 3‑2‑7, Miyamachi,
Mito, Ibaraki 310‑0015, Japan. 2Division of Medical Education, Juntendo University School of Medicine, Tokyo,
Japan. 3Department of Information and Computer Technology, Faculty of Engineering, Tokyo University of
Science, Tokyo, Japan. 4Department of Diagnostic and Generalist Medicine, Dokkyo Medical University Hospital,
Tochigi, Japan. 5Division of General Medicine, Center for Community Medicine, Jichi Medical University, Tochigi,
Japan. 6Department of General Medicine, Chiba University Hospital, Chiba, Japan. 7Immuno‑Rheumatology
Center, St. Luke’s International Hospital, Tokyo, Japan. 8Department of General Internal Medicine, Shonan
Kamakura General Hospital, Kamakura, Japan. 9Department of Patient Safety, Nagoya University Hospital, Aichi,
Japan. 10Muribushi Okinawa for Teaching Hospitals, Okinawa, Japan. *email: hrkoba1@gmail.com
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quality of resident ­education6. A previous study found that resident self-study time and in-training examination
scores increased until their working hours reached 60–65 h w­ eekly7,8. However, this decision raised concerns
about resident well-being because an 80-h limit of overtime per month is twice the standards of death due tooverwork (the so-called "karoshi line"). However, few studies have examined DHs’ impact on health, and there
is currently insufficient evidence to determine the appropriate DH limit in Japan.
Long working hours have negative effects on residents’ health, and can result in increased burnout and­depression9,10. In a cross-sectional study of 604 residents across Japan, residents experienced burnout 28.5% of
the time, and residents who reported that overwork caused their stress were 2.75 times more likely to experience­burnout11. Another study reported that doctors working ≥ 70 h weekly were 1.8 times more likely to be depressedthan those working ≤ 54 h w­ eekly12. A study by Ogawa et al. involving 1241 residents found that working > 80 hweekly was associated with developing depressive ­symptoms13. Occupational stress, job dissatisfaction, andshort sleep are associated with burnout and poor mental h­ ealth11,12,14. While these studies clearly demonstrate
the relationship between excessively long DHs and poor mental health among Japanese residents, there are some
limitations in determining appropriate DH limits. First, the numbers of residents participating in these studies
were relatively small and may not be representative of all residents. Second, these studies categorized DHs into
only a few categories; as a result, the point where mental health problems increase is unclear. Third, most ofthese studies measured only one aspect of mental health and its relationship with DHs. We expected burnout anddepression to be similarly related to weekly DHs; however, stress and satisfaction may have different relationships.
This study involved a multicenter, nationwide, cross-sectional survey of postgraduate residents who took
the General Medicine In-training Examination (GM-ITE), which is taken by about one-third of all residents inJapan. We evaluated the association between weekly DHs and psychological health-related outcomes (depression,
burnout, job stress, and job satisfaction) to determine the appropriate DH limit.

Methods

Participants and data collection. We conducted a survey of postgraduate year 1 (PGY-1) and 2 (PGY-2)
residents in Japan between January 18 and 31, 2020. After graduating from a 6-year medical school, students inJapan enter a 2-year postgraduate training ­program15,16. This training program is administered by the MHLW
and aims to develop basic clinical skills, regardless of future specialty. Residents were assigned to a program at
a community or university hospital as the core training hospital. Students can apply to the training hospital of
their choice. After the 2-year program, most residents entered specialty-based training.
The survey was distributed to residents who took the GM-ITE in the 2020 academic year. The GM-ITE is an
examination of general clinical knowledge and its application; used to assess individual residents and residency­programs17,18. The Specified Nonprofit Corporation of the Japan Institute for Advancement of Medical Education
Program (JAMEP) develops the examination annually with experienced doctors and peer reviewers. The exam
is voluntary for each training hospital, and approximately one-third of residents take it every year. Immediately
after the GM-ITE, participants completed a questionnaire to evaluate their work environment. The researchconsent form clearly stated that participation was voluntary and that responses would remain anonymous. All
participants provided written informed consent. This study was approved by the Ethics Review Board of the
JAMEP. This study was conducted in accordance with the Declaration of Helsinki.
Measurements. The survey asked about residents’ characteristics (age, sex, PGY, and preferences of spe-cialty), work environment factors (weekly duty hours, type of residency hospital, hospital area, experience ofcase-report writing or conference presentations, number of assigned inpatients, number of emergency department (ED) duties per month, and daily self-study time), and psychological health outcomes (burnout, depression, stress, and satisfaction).
The dependent variables were depression, burnout, job stress, and job satisfaction. This study was limited by
the number of questions asked; thus, a brief scale was used to assess these variables. Depression was assessed by
the Japanese version of the 2-item Patient Health Questionnaire (PHQ-2)19. The questionnaire is a simple screening tool for detecting depression and consists of two items: a loss of interest or pleasure and depressed mood overthe past 2 ­weeks20. Responses were dichotomous (yes/no), and a “yes” response for either question indicated apositive depression screening. The questionnaire has a sensitivity of 0.76 and a specificity of 0.87 for identifying
clinically significant ­depression21. The 10-item Mini-Z 2.0 survey was used to assess burnout, job stress, andjob satisfaction. The Mini-Z evaluates doctors’ wellbeing-related outcomes and related workplace s­ tressors22.
Burnout, stress, and satisfaction were assessed with a single question. A single-item measure of burnout (SMB)
was used to assess burnout, and respondents selected one of five options to indicate the level of burnout. The
validation of the SMB was assessed in previous studies and was well correlated with emotional exhaustion anddepersonalization on the Maslach Burnout Inventory, which are both core concepts of ­burnout23–25. Stress andsatisfaction were rated on a 5-point Likert scale. A Japanese version of Mini-Z has been developed and validated
for Japanese ­doctors26. Each question and its scoring are provided in the Appendix 1.
The independent variable of main interest was the self-reported average weekly DHs for the entire training
period. It was calculated as the total of weekday work, night ED duty, and weekend work (see Appendix 1).
Weekly DHs consisted of seven categories: Category 1 (< 50 h), Category 2 (≥ 50 and < 60 h), Category 3 (≥ 60
and < 70 h), Category 4 (≥ 70 and < 80 h), Category 5 (≥ 80 and < 90 h), Category 6 (≥ 90 and < 100 h), and Category 7 (≥ 100 h). The MHLW defines working hours as the time spent by a worker engaged in work at the explicit
or implicit direction of the ­employer6.

Statistical analyses. The association between resident DHs and psychological outcomes was examinedin terms of PRs estimated by clustered log-linear “modified” Poisson models, in which hospital variation was
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accounted for as clusters in generalized estimating equations (GEEs). Considering that 60 h weekly is the basic
upper limit of DHs for all doctors, Category 3 (≥ 60 and < 70 h) was used as the reference for analysis. Those who
could not provide information about DHs or psychological outcomes were excluded from the analysis, because
we have no auxiliary variables other than adjusted covariates in the models to impute these missing data. The
models adjusted for gender, PGY, preference for specialty, hospital type, hospital region, scholarship activities,
number of assigned inpatients, number of ED duties per month, and daily self-study time. As a post-hoc analysis, we explored characteristics related to resident job satisfaction among the above and other variables using the
log-linear Poisson GEE model; the motivation for the analysis is indicated in the Results section. All analyses
were conducted using SAS version 9.4 (Cary, NC, USA). This study followed the STROBE guidelines.

Results

Basic characteristics and work conditions. In total, 7669 residents from 593 teaching hospitals (total
number of training hospitals: 1020 (2019) and 1017 (2020)) participated in the 2020 GM-ITE. Of these, 6816
responded to the survey for a response rate of 90%. Excluding residents with missing data, 6045 residents wereused for analysis. Participants’ basic characteristics and work conditions are listed in Table 1. Of those residents,
68.1% were men, 49.2% were PGY-2, 11.3% were from university hospitals, and 32.4% were from urban hospitals. There were positive trends between DHs and men (%), community hospitals (%), number of ED duties, andnumber of assigned inpatients.
Psychological health‑related outcomes. Among participants, 37.3% experienced depression, 21.6%
experienced burnout, and 39.2% had high job stress. In contrast, 62.3% were satisfied with their jobs. Residents
who worked more hours were more likely to experience depression, burnout, and high levels of stress; however, this was not associated with satisfaction (Fig. 1). Among the residents working > 100 h weekly, 45.9% weredepressed, 31.6% experienced burn out, and 51.2% were highly stressed.
Table 2 shows the PRs of mental health-related outcomes among DH categories. Compared to residents in
Category 3 (≥ 60 and 70 h; reference), residents in Category 7 (≥ 100 h; PR 1.21 from the multivariable-adjusted
model; 95% CI 1.04–1.41) were more likely to experience depression. The same trend was observed for burnout,
and there was more depression among residents in Categories 6 (≥ 90 and < 100 h; PR 1.36; 95% CI 1.11–1.66)
and 7 (PR 1.36; 95% CI 1.10–1.68) than Category 3. Excessive job stress was common among residents in Categories 6 (PR 1.20; 95% CI 1.04–1.38) and 7 (PR 1.26; 95% CI 1.07–1.48), but less common among residents in
Categories 1 (< 50 h; PR 0.86; 95%CI 0.77–0.96) and 2 (≥ 50 and < 60 h; PR 0.87; 95% CI 0.80–0.95) comparedto the reference. There was no difference in job satisfaction among the DH categories.
Resident job satisfaction and associated factors. No association was observed between job satisfac-

tion and DHs. In our post-hoc analysis, PGY-2 increased satisfaction, but hospital type and sex had no effect on
satisfaction (Table 3). Residents who chose internal medicine, surgery, general medicine, and emergency medicine as their career aspirations were more satisfied than those who chose “others.” More-satisfied residents weremore likely to spend more time on self-study, and those who received support for conference presentations weremore satisfied. The number of ED night duties was not related to satisfaction, nor were DHs. Low satisfaction
was observed among residents assigned < 0–4 inpatients.

Discussion

This is the largest study in Japan to examine the relationship between DHs and resident mental health. In thisstudy, weekly DHs were assessed in 10-h intervals, and findings showed that working > 90 h weekly increased
burnout and depression among residents. We also found that long DHs were associated with excessive job
stress. However, job satisfaction was unrelated to DHs, and the major factors for low satisfaction were specialty
orientation and less self-study time.
The present study showed that depression increase when working > 90 h weekly. Ogawa et al. and Tomioka
et al. reported that depression increased in residents who worked > 80 h and > 70 h weekly, r­ espectively12,13. The
results of the present study generally support those findings. It is a new finding that burnout, like depression, also
increases with DHs > 90 h weekly; however, although burnout and depression are considered distinct concepts,
they are conceptually similar in some ways, and it is possible that we are observing the same ­condition27. In ourstudy, stress was shown to be positively correlated with DHs. In a nationwide survey of Japanese residents, 26.0%
of burned-out residents reported excessive work hours as ­stressful11. Residents who are at high risk for burnout
may need to avoid working long hours. In addition, the difference between this study and previous studies is that
this study was conducted during the COVID-19 pandemic. During this pandemic, clinicians, including residents,
were subjected to considerable psychological stress, which led to depression and ­burnout28. In a study of Japanese
healthcare workers, younger age and fewer years of experience were associated with increased burnout, which
may have influenced the results of this s­ tudy29. On the other hand, some studies have reported that the pandemic
did not necessarily increase working hours but led to a decrease in working h­ ours30. Although not reported asa study, many hospitals in Japan removed residents from the COVID-19 front line as part of infection-control
measures. Therefore, the pandemic’s effect on the results of this study is unclear, and further research is needed.
As there was no significant relationship between job satisfaction and DHs in this study, we conducted a
post-hoc analysis to determine which factors were related to satisfaction. Although there are few studies on
resident satisfaction in Japan, one study found that men, scholarly activity, good compensation, and favorable
curriculum were associated with higher ­satisfaction31. In our analysis, the most notable factors for low satisfaction were career preference for "others" rather than internal medicine, surgery, general medicine, or emergency
medicine. The "others" are fields that require more specific specialty skills than those listed above, meaning
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Total

C1: < 50 h

C2: ≥ 50 and < 60 h

C3: ≥ 60 and < 70 h

C4: ≥ 70 and < 80 h

C5: ≥ 80 and < 90 h

C6: ≥ 90 and < 100 h

C7: ≥ 100 h

N = 6045

N = 861

N = 1687

N = 1580

N = 709

N = 741

N = 258

N = 209

Gender (%)
Men

68.1

64.0

68.5

67.7

70.7

68.3

57.1

76.1

Women

31.9

36.0

31.5

32.3

29.3

31.7

42.9

23.9

Postgraduate year (%)
PGY-1

50.8

51.3

51.4

50.4

50.2

51.0

51.9

48.3

PGY-2

49.2

48.7

48.6

49.7

49.8

49.0

48.1

51.7

University

11.3

17.0

11.7

10.5

10.7

8.6

7.0

6.2

University-affiliated

5.0

5.6

4.7

5.2

4.1

5.5

5.8

2.9

Community

83.8

77.5

83.6

84.3

85.2

85.8

87.2

90.9

Hospital type (%)

Hospital area (%)
Urban

32.4

32.5

30.4

32.5

36.5

33.6

32.2

30.1

Non-urban

67.6

67.5

69.6

67.5

63.5

66.4

67.8

69.9

Career (%)
Internal medicine

35.8

33.4

36.4

36.1

36.0

35.6

32.9

42.1

Surgery

20.8

20.2

18.3

21.3

21.3

25.5

19.8

21.1

General medicine

2.4

2.3

2.9

2.3

2.1

1.9

2.7

2.9

Emergency medicine

3.4

3.3

2.3

3.5

3.7

4.7

5.0

5.7

Others

37.5

40.8

40.1

36.8

36.7

32.3

39.1

28.2

Scholarship activity (%)
Case report

21.2

21.7

18.6

21.1

22.1

23.8

22.9

27.3

Presentation at conferences

37.1

33.2

36.0

37.7

37.7

40.4

41.1

37.8
0.5

ED duties per month (%)
0–1

3.7

9.5

4.6

2.7

1.8

0.9

0.8

1–2

15.3

25.9

17.7

12.2

12.6

12.4

7.8

5.3

3–5

70.2

59.5

71.9

75.6

70.7

69.5

68.6

63.6

6 or more

10.2

4.2

5.5

9.1

14.4

16.7

22.5

29.2

Unknown

0.5

0.8

0.4

0.4

0.6

0.4

0.0

1.4

Assigned inpatients (%)
0–4

23.5

33.8

28.0

22.8

18.2

14.3

15.1

10.0

5–9

59.9

55.5

61.5

59.6

63.0

63.0

55.4

49.3

0–14

11.3

7.8

7.1

12.4

14.0

13.9

20.5

21.5

15 or more

2.9

0.7

0.9

2.3

3.1

5.5

6.6

16.7

Unknown

2.5

2.2

2.5

2.8

1.6

3.2

2.3

2.4

Self-study time per day (%)
None

3.5

3.8

3.3

3.8

2.5

4.0

2.7

3.8

0–30 min

34.1

41.9

36.8

32.8

31.9

26.3

30.6

28.2

31–60 min

41.5

39.8

41.4

42.2

42.0

42.4

40.7

39.2

61–90 min

16.7

12.1

14.8

17.2

17.9

22.8

19.4

17.7

91 min or more

4.3

2.3

3.7

3.9

5.6

4.3

6.6

11.0

Table 1.  Basic characteristics and work conditions of postgraduate residents classified by duty hours. The
average weekly duty hours are based on the sum of weekday work duties, night ED duties, and weekend workduties. Abbreviations: C1–C7, Category 1 to Category 7; h, hours; PGY, postgraduate year; ED, emergency
department.

that residents who chose these fields are specialty-oriented. The low satisfaction level among specialty-oriented
residents is thought to be because the 2-year postgraduate training is generalist-oriented, with an emphasis on
acquiring general clinical skills. However, factors related to workload, such as DHs and number of night ED
duties, were not related to satisfaction level. Since generalist-oriented students are willing to spend a long timelearning during their training period, it is thought that their satisfaction level does not decrease. Since there isa strong relationship between satisfaction and the length of self-study time in this study, we need to determine
how to increase the satisfaction of residents with low satisfaction. However, since this is a cross-sectional study,
the causal relationship between resident satisfaction and each factor is unknown.
How do these results impact the setting of maximum DHs for residents in Japan? Starting in 2024, overtime
work for all doctors will be limited to 960 h per year (equivalent to a 60-h work week), and overtime workfor doctors in training will be limited to a maximum of 1860 h per year (equivalent to an 80-h work week)5,6.
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70.0%
61.6%

63.4%

63.8%

64.1%

62.8%
60.3%

59.5%
60.0%

51.2%
48.4%

50.0%
43.2%
40.1%

Proportion

39.5%

40.8%

45.9%

40.0%

43.0%

35.2%
38.9%
35.4%

35.9%

30.6%

36.3%

31.6%

34.0%

30.0%
23.8%
21.8%
19.5%

19.2%

19.7%

20.0%

10.0%

Depression (%)

Burnout (%)

High stress (%)

Satisfaction (%)

0.0%
C1

C2

C3

C4

C5

C6

C7

Duty hour categories

Figure 1.  The association between duty hours and psychological health-related outcomes. Note Figure showsthat depression, burnout, and high stress among residents appeared to increase with DHs; however, this was
not associated with satisfaction. The categories of resident duty hours weekly were: Category 1 (< 50), Category
2 (≥ 50 and < 60), Category 3 (≥ 60 and < 70), Category 4 (≥ 70 and < 80), Category 5 (≥ 80 and < 90), Category 6(≥ 90 and < 100), and Category 7 (≥ 100). Abbreviations: C1–C8 = Category 1 to Category 8.

Combining the current results with the results of previous studies on D
­ Hs7,8,12,13, we have illustrated the differences in mental health and other outcomes in Table 4 by DHs into three groups: < 60 h weekly, 60–80 h weekly,and > 80 h weekly. The conclusion that can be drawn from this table is that working > 80 h weekly negatively
impacts mental health, whereas working < 60 h weekly negatively impacts education. Therefore, the results ofthese studies provide a reasonable explanation for the MHLW policy, which allows residents to work up to 80 hweekly. Additionally, 80 h of work per week should be the upper limit of working hours in countries other thanJapan as well for protecting the health of resident physicians. In countries without an upper limit on DHs or an
upper limit that exceeds 80 h per week, policy makers might need to conduct research on resident health andreconsider settings for upper limits on DHs.
Several additional issues, however, must be considered to set the upper limit of DH. First, it is necessary toconsider the issue in terms of medical s­ afety3,32,33. Doctors and residents’ long working hours threaten patient
safety worldwide, and an investigation of the extent of their impact in Japan is strongly encouraged. Next, there
is a large range of overtime hours, from 960 to 1860 h per year (equivalent to 60–80 h weekly); further study isneeded to determine the acceptable level of working hours. Finally, there is a question of whether this limit isappropriate for all residents. The analyses of satisfaction showed that residents were not necessarily homogenousand had different needs. Reducing the upper limit of 1860 h per year may be an option to prevent specialtyoriented residents from receiving long hours of unwanted training.
This study has several limitations. First, it assessed mental health-related outcomes using simple scales that did
not confirm the diagnosis of burnout or depression. These scales were used to reduce the burden on residents, as
this study was conducted after the examination. In this study, burnout was assessed with the SMB; however, one
study demonstrated that self-diagnosis with the SMB reported less burnout than the Maslach Burnout Inventory,
which is the gold standard for diagnosis of ­burnout24. Therefore, it is possible that we may have underestimatedactual burnout. In addition, as noted above, the SMB does not correlate with reduced personal accomplishment,
which is one factor in burnout. Depression was assessed using the PHQ-2, which is only a screening tool. Second,the DHs in this study were self-reported, and may not have been accurate. In addition, the study did not consider
the differences between DHs in each rotation, but rather examined the average DHs for the entire training period.
Therefore, even if a resident’s DHs are of short durations overall, only some rotations may have outstandingly long
DHs, which may cause mental health problems. Third, we did not have data on participants’ underlying mental
health problems or personalities. This is important because mental health problems during medical school havebeen reported to be a predictor of the onset of depression and burnout during ­training34. Fourth, only one-thirdof all residents participated in the GM-ITE, which may have led to selection bias. Participation in the GM-ITE
is voluntary for training hospitals that emphasize education. Residents with mood or anxiety disorders may tend
not to select such hospitals because they value the work environment more than education. In addition, approximately 10% of examinees who took the GM-ITE were excluded from the analysis due to missing data, which may
also be related to selection bias. However, the basic characteristics of the residents excluded from the study weresimilar to those of the study participants, limiting the impact of this bias (Appendix 2). Fifth, it is not possible
to prove a causal relationship between DH and psychological outcomes due to the nature of the cross-sectional

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Univariable model
Outcome

Depression

Burnout

High stress

Satisfaction

Multivariable ­model†

DH categoryN

Outcome prevalence (%)

PR

95% CIPPR

95% CI

C1: < 50 h

861

39.5

1.09

0.98

1.22

0.128

1.07

0.96

1.20

0.213

C2: ≥ 50 and < 60 h

1687

35.9

0.99

0.90

1.08

0.807

0.99

0.90

1.08

0.829

C3: ≥ 60 and < 70 h

1580

36.3

1

Reference

1

ReferenceC4: ≥ 70 and < 80 h

709

34.0

0.94

0.83

1.06

0.297

0.94

0.83

1.06

0.290

C5: ≥ 80 and < 90 h

741

38.9

1.07

0.96

1.20

0.222

1.07

0.96

1.20

0.222

P

C6: ≥ 90 and < 100 h

258

43.0

1.19

1.02

1.38

0.030

1.15

0.99

1.34

0.061

C7: ≥ 100 h

209

45.9

1.27

1.08

1.49

0.004

1.21

1.04

1.41

0.016

C1: < 50 h

861

23.8

1.09

0.94

1.27

0.231

1.05

0.90

1.22

0.542

C2: ≥ 50 and < 60 h

1687

19.5

0.90

0.78

1.03

0.119

0.88

0.77

1.02

0.082

C3: ≥ 60 and < 70 h

1580

21.8

1

Reference

1

ReferenceC4: ≥ 70 and < 80 h

709

19.2

0.88

0.74

1.04

0.145

0.87

0.73

1.03

0.107

C5: ≥ 80 and < 90 h

741

19.7

0.90

0.76

1.08

0.259

0.91

0.77

1.09

0.303

C6: ≥ 90 and < 100 h

258

30.6

1.41

1.15

1.72

0.001

1.36

1.11

1.66

0.003

C7: ≥ 100 h

209

31.6

1.45

1.17

1.80

0.001

1.36

1.10

1.68

0.005

C1: < 50 h

861

35.4

0.88

0.79

0.98

0.025

0.86

0.77

0.96

0.007

C2: ≥ 50 and < 60 h

1687

35.2

0.88

0.80

0.96

0.004

0.87

0.80

0.95

0.002

C3: ≥ 60 and < 70 h

1580

40.1

1

Reference

1

ReferenceC4: ≥ 70 and < 80 h

709

40.8

1.02

0.92

1.13

0.743

1.02

0.92

1.14

0.643

C5: ≥ 80 and < 90 h

741

43.2

1.08

0.98

1.19

0.134

1.09

0.99

1.20

0.083

C6: ≥ 90 and < 100 h

258

48.4

1.21

1.04

1.40

0.012

1.20

1.04

1.38

0.013

C7: ≥ 100 h

209

51.2

1.28

1.09

1.50

0.003

1.26

1.07

1.48

0.005

C1: < 50 h

861

59.5

0.94

0.88

1.00

0.044

0.97

0.92

1.04

0.407

C2: ≥ 50 and < 60 h

1687

61.6

0.97

0.92

1.03

0.327

0.99

0.94

1.04

0.643

C3: ≥ 60 and < 70 h

1580

63.4

1

Reference

1

ReferenceC4: ≥ 70 and < 80 h

709

63.8

1.01

0.94

1.08

0.853

1.00

0.93

1.06

0.880

C5: ≥ 80 and < 90 h

741

64.1

1.01

0.95

1.08

0.725

0.99

0.93

1.06

0.768

C6: ≥ 90 and < 100 h

258

62.8

0.99

0.90

1.09

0.858

0.97

0.88

1.07

0.540

C7: ≥ 100 h

209

60.3

0.95

0.85

1.07

0.411

0.92

0.82

1.04

0.176

Table 2.  Association between resident duty hours and mental health outcomes (n = 6045). There was a higher
proportion of burnout and depression among residents with DHs > 90 h weekly. High stress was positively
correlated with DH; however, satisfaction was not. †Adjusted for gender, postgraduate year, hospital type,hospital region, specialty preference, scholarship activities (case report or conference presentation), numberof assigned inpatients, number of ED duties per month, and self-study time per day. DH, duty hour; PR,prevalence ratio; CI, confidence interval; C1–C8, Categories 1 to 8; h, hours.

study. However, this study was designed to assess the impact of DHs on mental health by considering the temporal relationship between "past DH" and "current mental health status.” Moreover, since both items were to be
responded to at the same time, there may be response bias in both responses depending on actual mental healthstatus. Follow-up studies monitoring DHs and mental health status in the short to medium term are desirable.
In conclusion, these results suggest that depression, burnout, and job stress may increase in postgraduate
residents with DHs ≥ 90 h weekly. This study partially supports the 80-h work week limit in terms of resident
well-being, but this limit should also be considered from the perspectives of resident education, medical safety,
and workers’ rights.

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Prevalence ratio

95% CI

P valueMen (vs. Women)

0.97

0.93–1.02

0.248

PGY-2 (vs. PGY-1)

1.07

1.02–1.11

0.005

Hospital typeCommunity

Reference

University

0.93

0.85–1.01

0.085

University-affiliated0.91

0.79–1.05

0.187

Urban

0.98

0.94–1.03

0.527

Career preference
Internal medicine

Reference

Surgery

1.01

0.95–1.06

0.815

General medicine

1.01

0.89–1.15

0.842

Emergency medicine

1.01

0.39–1.13

0.790

Others0.90

0.86–0.95

0.000

Case report (yes vs. no)

0.97

0.92–1.01

0.165

Presentation at conferences (yes vs. no)

0.95

0.90–0.99

0.017

Self-study time
0–30 min

Reference

31–60 min

1.09

1.04–1.15

0.000

61–90 min

1.19

1.13–1.25

0.000

91 min or more

1.20

1.10–1.31

0.000

None

0.72

0.61–0.86

0.000Night ED duty0

Reference

1–2

0.91

0.78–1.06

0.215

3–5

0.97

0.84–1.11

0.638

6 or more

0.96

0.82–1.11

0.567

Unknown

0.72

0.45–1.13

0.152

Assigned inpatients
0–4

Reference

5–9

1.08

1.02–1.14

0.004

10–14

1.10

1.02–1.19

0.014

15 or more

0.99

0.86–1.13

0.836

Unknown

0.87

0.74–1.03

0.108

Table 3.  Estimates of the ratios of proportions satisfied among residents’ and their hospitals’ characteristics.
PGY, postgraduate year; ED, emergency department.

Weekly duty hours< 60 h60–80 h> 80 hBurnout11→→↑

Depression12,13

→

→

↑

Stress↓→↑Satisfaction

→

→

→

In-training exam ­score8

↓

→

→

Self-study ­time7

↓

→

→

Patient safety

?

?

?

Mental health (our study)

Education

Table 4.  The summary of evidence related to duty hours and postgraduate residents in Japan. This table shows
the factors associated with duty hours of postgraduate residents in Japan. Using 60–80 h weekly (equivalent to80–120 h of overtime per month) as a reference point, the table shows how these factors change when working
less than 60 h weekly or more than 80 h weekly. The references corresponding to each item are presented in thetable.

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Data availability

Due to the nature of this research, participants of this study did not agree for their data to be shared publicly, so
supporting data is not available.
Received: 7 February 2022; Accepted: 15 June 2022

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Acknowledgements

We thank members of the JAMEP, the question development committee, and the peer-review committee of theGeneral Medicine In-training Examination for their assistance. The authors would like to thank Editage (https://​www.​edita​ge.​jp) for English language review.

Author contributions

K.N.: conceptualization, writing—original draft, methodology, software, formal analysis, and visualization; Y.N.
Conceptualization, investigation, resources, writing—review and editing, supervision, project administration,and funding acquisition; T. S.: Conceptualization, writing, reviewing, and editing; T. S.: Investigation; Y. Y. Investigation; K. S.: Investigation; S. F.: Investigation; S. N.: Investigation; M. K.: Investigation; K. K.: Formal analysis;
Y. T.: Conceptualization and supervision; and H. K.: Conceptualization, writing-review and editing, supervision.

Competing interests

This work was supported by the Health, Labour, and Welfare Policy Grants of Research on Region Medical(21A2004) from the Ministry of Health, Labour, and Welfare. Dr. Nishizaki received an honorarium from JAMEP
as GM-ITE project manager. Dr. Shinozaki received an honorarium from JAMEP as full-time research and statistical adviser. Dr. Tokuda is the JAMEP director. Dr. Kobayashi and Dr. Shikino received an honorarium fromJAMEP as speakers of the JAMEP lecture. Dr. Shimizu, Dr. Yamamoto, Dr. Shikino, and Dr. Fukui received anhonorarium from JAMEP as exam preparers of GM-ITE. Dr. Nishizaki, Dr. Shinozaki, Dr. Tokuda, Dr. Kobayashi,
Dr. Shimizu, Dr. Yamamoto, Dr. Shikino, and Dr. Fukui were not involved in this analysis.

Additional information

Supplementary Information The online version contains supplementary material available at https://​doi.​org/​
10.​1038/​s41598-​022-​14952-x.
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