Table 1 Characteristics of study participants

N

33

271

42

534

Age [years], mean ± SD

43.1 ± 11.1

39.8 ± 10.4

0.18

39.5 ± 12.0

36.5 ± 11.3

0.099

Body mass index [kg/m²], mean ± SD

23.2 ± 2.9

23.6 ± 4.0

0.78

23.6 ± 4.0

21.5 ± 3.7

0.75

Monthly overtime hours [hours], mean ± SD

27.7 ± 26.1

35.1 ± 27.3

0.16

6.4 ± 5.2

8.7 ± 11.2

0.80

Sleep duration [hours], mean ± SD

6.4 ± 1.0

6.3 ± 1.0

0.48

6.2 ± 1.7

6.4 ± 1.1

0.20

Number of holidays [days/month], mean ± SD

7.7 ± 1.8

7.1 ± 2.0

0.16

9.7 ± 3.0

9.0 ± 2.2

0.025

Length of service [years], mean ± SD

15.8 ± 11.4

15.7 ± 10.4

0.86

13.4 ± 9.9

12.5 ± 10.1

0.39

GHQ-12 score, mean ± SD

3.5 ± 3.2

3.8 ± 3.4

0.69

4.1 ± 3.6

4.0 ± 3.3

0.99

Educational level, n (%)

0.58

1.00

High school graduate

10 (32.3)

80 (31.6)

6 (15.4)

77 (14.8)

Junior/technical college graduate

8 (25.8)

48 (19.0)

26 (66.7)

351 (67.4)

University degree or higher

13 (41.9)

125 (49.4)

7 (18.0)

93 (17.9)

Married, n (%)

22 (66.7)

186 (69.9)

0.69

22 (55.0)

263 (49.6)

0.62

Night-shift worker, n (%)

13 (40.6)

74 (28.4)

0.16

32 (78.1)

392 (74.8)

0.71

Current smoker, n (%)

7 (21.9)

106 (40.0)

0.054

8 (19.5)

56 (10.7)

0.12

Regular drinker, n (%)

14 (43.8)

125 (46.8)

0.85

11 (26.8)

111 (21.3)

0.43

Any unusual item in the results of the latest physical examination, n (%)

17 (54.8)

141 (56.4)

1.00

19 (45.2)

222 (45.5)

1.00

History of type 2 diabetes, n (%)

1 (3.3)

12 (5.3)

1.00

1 (2.8)

8 (1.8)

0.50

History of hypertension, n (%)

6 (19.4)

35 (15.1)

0.60

2 (5.6)

33 (7.3)

1.00

History of depression, n (%)

3 (10.0)

11 (4.9)

0.22

2 (5.6)

15 (3.3)

0.36