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Table 1 Mean values of baseline characteristics according to current shift work and tertile of shift work duration

From: Association between shift work and obesity among female nurses: Korean Nurses’ Survey

Variables Total Current shift work P-value Tertile of shift work duration P-value
No Yes Tertile 1 Tertile 2 Tertile 3
  (n = 9,989) (n = 4,702) (n = 5,287)   (n = 1,732) (n = 1,731) (n = 1,686)  
Age (years) 33.2 ± 8.6 37.6 ± 9.2 29.2 ± 5.6 <0.001 24.9 ± 2.9c 28.1 ± 3.1b 34.7 ± 5.1a <0.001
BMI (kg/m2) 20.9 ± 2.5 21.4 ± 2.6 20.5 ± 2.5 <0.001 20.0 ± 2.1c 20.2 ± 2.4b 21.3 ± 2.7a <0.001
Hypertension 220 (2.2) 193 (4.1) 27 (0.5) <0.001 3 (0.2) 6 (0.3) 16 (0.9) 0.003
Diabetes 43 (0.4) 31 (0.7) 12 (0.2) 0.001 3 (0.2) 4 (0.2) 5 (0.3) <0.001
Osteoporosis 102 (1.0) 79 (1.7) 23 (0.4) <0.001 1 (0.1) 6 (0.3) 13 (0.8) 0.003
Hyperlipidemia 57 (7.6) 472 (10.0) 285 (5.4) <0.001 40 (2.3) 78 (4.5) 165 (9.8) <0.001
Breast cancer 87 (0.9) 73 (1.6) 14 (0.3) <0.001 1 (0.1) 3 (0.2) 10 (0.6) 0.007
Current smoking status     0.335     <0.001
 No 9874 (98.8) 4653 (99.0) 5221 (98.8) 1697 (98.0) 1718 (99.2) 1675 (99.3)
 Yes 115 (1.2) 49 (1.0) 66 (1.2) 35 (2.0) 13 (0.8) 11 (0.7)
Regular drinking habit     <0.001     <0.001
 No 5144 (51.5) 2683 (57.1) 2461 (46.5) 625 (36.1) 788 (45.5) 993 (58.9)
 Yes 4845 (48.5) 2019 (42.9) 2826 (53.5) 1107 (63.9) 943 (54.5) 693 (41.1)
Marital status     <0.001     <0.001
 Married (remarriage) 4589 (45.9) 3087 (65.7) 1502 (28.4) 88 (5.1) 344 (19.9) 1032 (61.2)
 Cohabitation 16 (0.2) 6 (0.1) 10 (0.2) 3 (0.2) 2 (0.1) 4 (0.2)
 Divorced 246 (2.5) 127 (2.7) 119 (2.3) 31 (1.8) 42 (2.5) 40 (2.4)
 Widowed 36 (0.4) 34 (0.7) 2 (0.0) 0 (0.0) 0 (0.0) 2 (0.1)
 Never-married 5102 (51.1) 1448 (30.8) 3654 (69.1) 1610 (93.0) 1341 (77.5) 608 (36.1)
Family income     <0.001     <0.001
 Less than 30 million won 1259 (12.6) 490 (10.4) 769 (14.5) 401 (23.2) 247 (14.3) 96 (5.7)
 30-45 million won 2787 (27.9) 1002 (21.3) 1785 (33.8) 605 (34.9) 685 (39.6) 454 (26.9)
 45-75 million won 3545 (35.5) 1802 (38.3) 1743 (33.0) 472 (27.3) 522 (30.2) 699 (41.5)
 More than 75 million won 2389 (24.0) 1408 (29.9) 990 (18.7) 254 (14.7) 277 (16.0) 437 (25.9)
Education     <0.001     <0.001
 Graduation from three-year course 3469 (34.7) 1294 (27.5) 2175 (41.1) 845 (48.8) 733 (42.3) 528 (31.3)
 Graduation from four-year course 4839 (48.4) 2083 (44.3) 2756 (52.1) 880 (50.8) 954 (55.1) 862 (51.1)
 Graduate school or higher 1681 (16.8) 1325 (28.2) 356 (6.7) 7 (0.4) 44 (2.5) 296 (17.6)
Dietary habits         
 Breakfast skipping 3649 (36.5) 1371 (29.2) 2278 (43.1) <0.001 749 (43.2) 815 (47.1) 647 (38.4) <0.001
 Lunch skipping 129 (1.3) 23 (0.5) 106 (2.0) <0.001 50 (2.9) 35 (2.0) 19 (1.1) <0.001
 Dinner skipping 96 (1.0) 38 (0.8) 58 (1.1) 0.140 20 (1.2) 23 (1.3) 14 (0.8) <0.001
Regular exercise     <0.001     <0.001
 No 5588 (55.9) 2478 (52.7) 3110 (58.8) 1063 (61.4) 957 (55.3) 1010 (59.9)
 Yes 4401 (44.1) 2224 (47.3) 2177 (41.2) 669 (38.6) 774 (44.7) 676 (40.1)
Sleep problems, during the last 2 weeks     <0.001     <0.001
 Never 4540 (45.4) 2815 (59.9) 1725 (32.6) 477 (27.5) 494 (28.5) 707 (41.9)
 1-6 days 3538 (35.4) 1414 (30.1) 2124 (40.2) 685 (39.5) 702 (40.6) 679 (40.3)
 7-13 days 1187 (11.9) 304 (6.5) 883 (16.7) 333 (19.2) 331 (19.1) 202 (12.0)
 Every day 724 (7.2) 169 (3.6) 555 (10.5) 237 (13.7) 204 (11.8) 98 (5.8)
Self-perceived health status     <0.001     0.003
 Very good 716 (7.2) 389 (8.3) 327 (6.2) 119 (6.9) 105 (6.1) 92 (5.5)
 Good 4545 (45.5) 2219 (47.2) 2326 (44.0) 804 (46.4) 756 (43.7) 710 (42.1)
 Fair 3837 (38.4) 1735 (36.9) 2102 (39.8) 662 (38.2) 666 (38.5) 716 (42.5)
 So-so 753 (7.5) 290 (6.2) 463 (8.8) 134 (7.7) 174 (10.1) 143 (8.5)
 Bad 138 (1.4) 69 (1.5) 69 (1.3)   13 (0.8) 30 (1.7) 25 (1.5)  
  1. Data are expressed as mean ± SD or percentage. Statistical differences between groups were compared with independent sample t-test and one-way ANOVA for continuous variables and chi-square test for categorical variables.
  2. a, b, cThe same letters indicate non-significant difference between groups based on Duncan’s multiple comparison test.