Association between Shift Work and Neurocognitive Function among Firefighters in South Korea: A Prospective before–after Study
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Subjects
2.2. Type of Shift Work
2.3. Questionnaire
2.4. Sleep Disorder and Depression Evaluation Tools
2.5. Neurocognitive Function Testing
2.6. Study Endpoints
2.7. Statistical Analysis
2.8. Ethics Statement
3. Results
3.1. General Characteristics of Subjects
3.2. Neurocognitive Function
3.3. Stratifying Analysis Based on the ISI
3.4. Stratifying Analysis Based on the PHQ-9
3.5. Multivariate Analysis for the Changes of Neurocognitive Function
4. Discussion
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Characteristics | Shift Work Schedule | All Subjects N = 352 | p-Value | |||
---|---|---|---|---|---|---|
3-Day Cycle N = 71 | 6-Day Cycle N = 77 | 9-Day Cycle N = 83 | 21-Day Cycle N = 121 | |||
Age (years) | 0.043 3–6 | |||||
20–29 | 4 (5.6%) | 11 (14.3%) | 11 (13.3%) | 14 (11.6%) | 40 (11.4%) | |
30–39 | 21 (29.6%) | 35 (45.5%) | 29 (34.9%) | 47 (38.8%) | 132 (37.5%) | |
40–49 | 30 (42.3%) | 19 (24.7%) | 24 (28.9%) | 48 (39.7%) | 121 (34.4%) | |
50–59 | 16 (22.5%) | 12 (15.6%) | 19 (22.9%) | 12 (9.9%) | 59 (16.8%) | |
Mean ± SD | 42.5 ± 8.1 | 38.4 ± 9.3 | 41.2 ± 9.0 | 39.1 ± 8.0 | 40.1 ± 8.7 | 0.012 3–6,3–21 |
Sex | 0.051 | |||||
Men | 61 (85.9%) | 73 (94.8%) | 80 (96.4%) | 114 (94.2%) | 328 (93.2%) | |
Women | 10 (14.1%) | 4 (5.2%) | 3 (3.6%) | 7 (5.8%) | 24 (6.8%) | |
Job | 0.009 3–21,6–21 | |||||
Fire suppression | 14 (19.7%) | 21 (27.3%) | 25 (30.1%) | 51 (42.1%) | 111 (31.5%) | |
Others | 57 (80.3%) | 56 (72.7%) | 58 (69.9%) | 70 (57.9%) | 241 (68.5%) | |
Education | 0.046 3–6,6–21 | |||||
High school | 10 (14.1%) | 24 (31.2%) | 18 (21.7%) | 18 (14.9%) | 70 (19.9%) | |
2-year degree | 23 (32.4%) | 23 (29.9%) | 18 (21.7%) | 36 (29.7%) | 100 (28.4%) | |
4-year degree | 38 (53.5%) | 30 (39.0%) | 47 (56.6%) | 67 (55.4%) | 182 (51.7%) | |
Monthly income | <0.001 3–6,3–21,6–9,9–21 | |||||
Missing | 0 | 0 | 2 | 0 | 2 | |
Low | 11 (15.5%) | 33 (42.9%) | 12 (14.8%) | 37 (30.6%) | 93 (26.6%) | |
Middle | 32 (45.1%) | 32 (41.6%) | 42 (51.9%) | 62 (51.2%) | 168 (48.0%) | |
High | 28 (39.4%) | 12 (15.6%) | 27 (33.3%) | 22 (18.2%) | 89 (25.4%) | |
Smoking | 0.576 | |||||
Missing | 0 | 0 | 0 | 1 | 1 | |
Never | 29 (40.8%) | 37 (48.0%) | 33 (39.8%) | 40 (33.3%) | 139 (39.6%) | |
Past smoker | 24 (33.8%) | 22 (28.6%) | 21 (25.3%) | 45 (37.5%) | 112 (31.9%) | |
Current light smoker | 10 (14.1%) | 10 (13.0%) | 17 (20.5%) | 21 (17.5%) | 58 (16.5%) | |
Current heavy smoker | 8 (11.3%) | 8 (10.4%) | 12 (14.5%) | 14 (11.7%) | 42 (12.0%) | |
Alcohol | 0.996 | |||||
Missing | 2 | 3 | 1 | 2 | 8 | |
No | 15 (21.7%) | 17 (23.0%) | 16 (19.5%) | 24 (20.2%) | 72 (20.9%) | |
Normal drinking | 41 (59.4%) | 41 (55.4%) | 48 (58.5%) | 69 (58.0%) | 199 (57.9%) | |
Heavy drinking | 13 (18.8%) | 16 (21.6%) | 18 (22.0%) | 26 (21.8%) | 73 (21.2%) | |
Regular exercise | 0.636 | |||||
No | 33 (46.5%) | 36 (46.8%) | 44 (53.0%) | 53 (43.8%) | 166 (47.2%) | |
Yes | 38 (53.5%) | 41 (53.2%) | 39 (47.0%) | 68 (56.2%) | 186 (52.8%) | |
Caffeine | 0.045 3–6,3–9 | |||||
Missing | 5 | 7 | 2 | 4 | 18 | |
No | 8 (12.1%) | 16 (22.9%) | 15 (18.5%) | 18 (15.4%) | 57 (17.1%) | |
Light coffee drinking | 25 (37.9%) | 35 (50.0%) | 45 (55.6%) | 61 (52.1%) | 166 (49.7%) | |
Moderate to heavy coffee drinking | 33 (50.0%) | 19 (27.1%) | 21 (25.9%) | 38 (32.5%) | 111 (33.2%) | |
Insomnia | 0.148 | |||||
Normal (≤ 7) | 43 (60.6%) | 31 (40.3%) | 44 (53.0%) | 68 (56.2%) | 186 (52.8%) | |
Mild Insomnia (8–14) | 21 (29.6%) | 40 (51.9%) | 32 (38.6%) | 41 (33.9%) | 134 (38.1%) | |
Insomnia (≥ 15) | 7 (9.9%) | 6 (7.8%) | 7 (8.4%) | 12 (9.9%) | 32 (9.1%) | |
Mean ± SD | 7.3 ± 2.2 | 8.8 ± 2.4 | 7.7 ± 4.7 | 7.2 ± 5.3 | 7.7 ± 5.0 | 0.151 |
Depression | 0.896 | |||||
Normal (≤ 4) | 60 (84.5%) | 64 (83.1%) | 71 (85.5%) | 103 (85.1%) | 298 (84.7%) | |
Mild depression (5–9) | 9 (12.7%) | 9 (11.7%) | 11 (13.3%) | 14 (11.6%) | 43 (12.2%) | |
Depression (≥ 10) | 2 (2.8%) | 4 (5.2%) | 1 (1.2%) | 4 (3.3%) | 11 (3.1%) | |
Mean ± SD | 2.2 ± 2.8 | 2.4 ± 3.1 | 2.1 ± 2.3 | 2.0 ± 2.9 | 2.1 ± 2.8 | 0.771 |
Domain | Mean ± SD (N = 352) | p-Value | |
---|---|---|---|
During Day Work | After Night Work | ||
Composite memory | 90.6 ± 19.1 | 84.7 ± 19.7 | <0.001 |
Verbal memory | 87.7 ± 20.0 | 81.3 ± 21.9 | <0.001 |
Visual memory | 97.1 ± 16.3 | 94.0 ± 16.6 | 0.001 |
Complex attention | 97.8 ± 18.2 | 93.3 ± 32.4 | 0.007 |
Psychomotor speed | 112.4 ± 15.4 | 110.1 ± 15.2 | <0.001 |
Motor speed | 111.0 ± 15.1 | 108.7 ± 14.1 | <0.001 |
Processing speed | 107.6 ± 15.7 | 107.4 ± 17.1 | 0.860 |
Reaction time | 92.4 ± 15.0 | 92.7 ± 17.1 | 0.711 |
Cognitive flexibility | 106.2 ± 16.9 | 105.8 ± 19.1 | 0.671 |
Executive functioning | 107.0 ± 16.5 | 107.2 ± 18.5 | 0.799 |
Neurocognitive index | 99.9 ± 11.6 | 97.4 ± 13.4 | <0.001 |
Domain | ISI Category | N | Mean ± SD (n = 352) | p-Value | |
---|---|---|---|---|---|
During Daytime Work | Post Nighttime Work | ||||
Composite memory | Normal | 186 | 90.2 ± 20.1 | 84.8 ± 19.5 | <0.001 |
Mild insomnia | 134 | 90.6 ± 17.2 | 85.4 ± 19.4 | 0.002 | |
Insomnia | 32 | 92.8 ± 21.6 | 81.5 ± 21.9 | 0.012 | |
Verbal memory | Normal | 186 | 87.7 ± 20.6 | 82.7 ± 22.5 | <0.001 |
Mild insomnia | 134 | 87.4 ± 19.1 | 80.4 ± 20.3 | <0.001 | |
Insomnia | 32 | 89.7 ± 20.1 | 77.2 ± 24.6 | 0.001 | |
Visual memory | Normal | 186 | 96.6 ± 16.8 | 92.8 ± 15.8 | 0.006 |
Mild insomnia | 134 | 97.6 ± 14.9 | 95.8 ± 17.1 | 0.269 | |
Insomnia | 32 | 98.3 ± 18.9 | 92.8 ± 18.6 | 0.110 | |
Complex attention | Normal | 186 | 96.1 ± 20.3 | 94.3 ± 23.7 | 0.260 |
Mild insomnia | 134 | 100.1 ± 15.0 | 92.2 ± 43.3 | 0.027 | |
Insomnia | 32 | 98.2 ± 17.0 | 92.7 ± 22.4 | 0.227 | |
Psychomotor speed | Normal | 186 | 111.7 ± 16.5 | 110.2 ± 15.9 | 0.056 |
Mild insomnia | 134 | 114.1 ± 14.5 | 111.5 ± 14.5 | 0.008 | |
Insomnia | 32 | 109.3 ± 11.3 | 104.3 ± 13.5 | 0.069 | |
Motor speed | Normal | 186 | 110.1 ± 15.8 | 108.6 ± 14.7 | 0.053 |
Mild insomnia | 134 | 112.2 ± 14.8 | 108.3 ± 13.5 | 0.001 | |
Insomnia | 32 | 111.4 ± 12.1 | 104.8 ± 13.6 | 0.007 | |
Processing speed | Normal | 186 | 107.7 ± 15.9 | 106.5 ± 16.9 | 0.298 |
Mild insomnia | 134 | 109.1 ± 15.9 | 110.2 ± 17.4 | 0.341 | |
Insomnia | 32 | 100.8 ± 11.3 | 101.4 ± 15.0 | 0.845 | |
Reaction time | Normal | 186 | 92.4 ± 15.2 | 92.3 ± 16.8 | 0.931 |
Mild insomnia | 134 | 93.5 ± 15.2 | 93.3 ± 17.3 | 0.872 | |
Insomnia | 32 | 88.5 ± 12.3 | 93.0 ± 19.2 | 0.190 | |
Cognitive flexibility | Normal | 186 | 104.8 ± 18.8 | 105.1 ± 18.9 | 0.809 |
Mild insomnia | 134 | 108.4 ± 14.0 | 106.8 ± 20.1 | 0.306 | |
Insomnia | 32 | 105.3 ± 15.4 | 106.0 ± 15.8 | 0.821 | |
Executive functioning | Normal | 186 | 105.6 ± 18.3 | 106.6 ± 18.3 | 0.426 |
Mild insomnia | 134 | 109.2 ± 13.8 | 108.0 ± 19.8 | 0.414 | |
Insomnia | 32 | 105.8 ± 15.2 | 108.0 ± 14.7 | 0.397 | |
Neurocognitive index | Normal | 186 | 99.0 ± 13.0 | 97.3 ± 12.7 | 0.009 |
Mild insomnia | 134 | 101.4 ± 9.6 | 97.9 ± 14.9 | 0.001 | |
Insomnia | 32 | 98.9 ± 10.9 | 95.4 ± 10.3 | 0.089 |
Domain | PHQ-9 Category | N | Mean ± SD (n = 352) | p-Value | |
---|---|---|---|---|---|
During Daytime Work | Post Nighttime Work | ||||
Composite memory | Normal | 298 | 90.1 ± 19.1 | 84.6 ± 19.7 | <0.001 |
Depression | 54 | 93.3 ± 19.4 | 85.3 ± 19.7 | 0.003 | |
Verbal memory | Normal | 298 | 87.3 ± 19.8 | 81.1 ± 22.0 | <0.001 |
Depression | 54 | 90.1 ± 20.9 | 82.7 ± 21.3 | <0.001 | |
Visual memory | Normal | 298 | 96.8 ± 16.3 | 94.0 ± 16.3 | 0.010 |
Depression | 54 | 99.1 ± 16.4 | 93.8 ± 18.4 | 0.040 | |
Complex attention | Normal | 298 | 97.2 ± 19.0 | 93.1 ± 34.0 | 0.030 |
Depression | 54 | 101.0 ± 12.7 | 94.5 ± 22.1 | 0.017 | |
Psychomotor speed | Normal | 298 | 112.3 ± 15.8 | 111.0 ± 15.0 | 0.035 |
Depression | 54 | 112.9 ± 13.5 | 105.4 ± 15.9 | <0.001 | |
Motor speed | Normal | 298 | 110.6 ± 15.5 | 108.6 ± 14.1 | 0.002 |
Depression | 54 | 113.2 ± 12.7 | 105.8 ± 14.3 | <0.001 | |
Processing speed | Normal | 298 | 108.1 ± 15.9 | 108.6 ± 16.9 | 0.626 |
Depression | 54 | 104.5 ± 14.2 | 101.2 ± 16.8 | 0.143 | |
Reaction time | Normal | 298 | 92.7 ± 15.1 | 92.5 ± 17.3 | 0.808 |
Depression | 54 | 90.8 ± 14.5 | 93.7 ± 16.4 | 0.142 | |
Cognitive flexibility | Normal | 298 | 106.0 ± 17.4 | 105.9 ± 19.0 | 0.921 |
Depression | 54 | 107.6 ± 14.1 | 105.6 ± 19.7 | 0.471 | |
Executive functioning | Normal | 298 | 106.8 ± 16.9 | 107.4 ± 18.4 | 0.545 |
Depression | 54 | 108.2 ± 13.7 | 106.6 ± 19.4 | 0.544 | |
Neurocognitive index | Normal | 298 | 99.7 ± 12.0 | 97.4 ± 13.6 | <0.001 |
Depression | 54 | 101.1 ± 9.4 | 96.9 ± 12.1 | 0.003 |
Domain | Type of Shift Work | Model 1 | Model 2 | Model 3 | |||
---|---|---|---|---|---|---|---|
LSmeans | p-Value | LSmeans | p-Value | LSmeans | p-Value | ||
Composite memory | 3-day cycle | 8.38 | 0.503 | 9.26 | 0.493 | 8.68 | 0.483 |
6-day cycle | 4.74 | 5.06 | 4.59 | ||||
9-day cycle | 3.81 | 4.82 | 4.18 | ||||
21-day cycle | 6.50 | 7.35 | 7.07 | ||||
Verbal memory | 3-day cycle | −20.17 | 0.030 | −15.78 | 0.060 | −15.92 | 0.071 |
6-day cycle | −15.49 9 | −12.13 | −12.07 | ||||
9-day cycle | −25.95 6,21 | −13.01 | −21.21 | ||||
21-day cycle | −17.19 9 | −15.78 | −12.68 | ||||
Visual memory | 3-day cycle | 6.20 | 0.327 | 6.39 | 0.246 | 5.34 | 0.313 |
6-day cycle | 1.30 | 0.61 | 0.12 | ||||
9-day cycle | 1.49 | 1.30 | 0.69 | ||||
21-day cycle | 3.79 | 3.59 | 3.29 | ||||
Complex attention | 3-day cycle | 0.21 | 0.563 | 0.29 | 0.499 | −0.15 | 0.547 |
6-day cycle | 7.03 | 7.75 | 6.86 | ||||
9-day cycle | 4.11 | 4.53 | 4.29 | ||||
21-day cycle | 5.63 | 6.50 | 6.32 | ||||
Psychomotor speed † | 3-day cycle | 2.04 | 0.307 | 2.40 | 0.215 | 1.81 | 0.279 |
6-day cycle | 0.31 | 0.10 | −0.41 | ||||
9-day cycle | 3.66 | 3.96 | 3.15 | ||||
21-day cycle | 2.71 | 2.68 | 2.15 | ||||
Motor speed ‡ | 3-day cycle | 4.21 | 0.131 | 3.25 | 0.075 | 3.20 | 0.112 |
6-day cycle | 3.14 | 1.92 | 1.69 | ||||
9-day cycle | 4.31 | 3.29 | 2.81 | ||||
21-day cycle | 1.00 | −0.39 | −0.50 | ||||
Processing speed †† | 3-day cycle | −2.66 21 | <0.001 | −0.23 21 | <0.001 | −1.47 21 | <0.001 |
6-day cycle | −4.21 9,21 | −2.37 9,21 | −2.93 9,21 | ||||
9-day cycle | 1.12 6 | 3.60 6 | 2.64 6 | ||||
21-day cycle | 3.88 3,6 | 6.36 3,6 | 5.50 3,6 | ||||
Reaction time | 3-day cycle | −0.69 | 0.986 | 1.64 | 0.907 | 2.52 | 0.860 |
6-day cycle | −0.56 | 0.71 | 1.47 | ||||
9-day cycle | 0.04 | 2.41 | 3.50 | ||||
21-day cycle | −0.09 | 1.57 | 2.41 | ||||
Cognitive flexibility | 3-day cycle | −3.24 21 | <0.001 | −3.02 21 | <0.001 | −2.88 21 | <0.001 |
6-day cycle | −3.74 21 | −4.53 21 | −4.62 21 | ||||
9-day cycle | 0.20 21 | −0.36 21 | −0.05 21 | ||||
21-day cycle | 5.25 3,6,9 | 4.90 3,6,9 | 5.18 3,6,9 | ||||
Executive functioning | 3-day cycle | −3.52 21 | <0.001 | −3.21 21 | <0.001 | −3.10 21 | <0.001 |
6-day cycle | −4.78 21 | −5.51 21 | −5.39 21 | ||||
9-day cycle | −0.46 21 | −0.83 21 | −0.59 21 | ||||
21-day cycle | 4.77 3,6,9 | 4.42 3,6,9 | 4.80 3,6,9 | ||||
Neurocognitive index | 3-day cycle | 1.46 | 0.291 | 2.19 | 0.269 | 1.52 | 0.225 |
6-day cycle | 1.57 | 1.77 | 2.92 | ||||
9-day cycle | 2.35 | 3.00 | 4.55 | ||||
21-day cycle | 3.99 | 4.53 | 2.07 |
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Kwak, K.; Kim, B.-K.; Jang, T.-W.; Sim, C.S.; Ahn, Y.-S.; Choi, K.-S.; Jeong, K.S. Association between Shift Work and Neurocognitive Function among Firefighters in South Korea: A Prospective before–after Study. Int. J. Environ. Res. Public Health 2020, 17, 4647. https://doi.org/10.3390/ijerph17134647
Kwak K, Kim B-K, Jang T-W, Sim CS, Ahn Y-S, Choi K-S, Jeong KS. Association between Shift Work and Neurocognitive Function among Firefighters in South Korea: A Prospective before–after Study. International Journal of Environmental Research and Public Health. 2020; 17(13):4647. https://doi.org/10.3390/ijerph17134647
Chicago/Turabian StyleKwak, Kyeongmin, Bong-Kyu Kim, Tae-Won Jang, Chang Sun Sim, Yeon-Soon Ahn, Kyeong-Sook Choi, and Kyoung Sook Jeong. 2020. "Association between Shift Work and Neurocognitive Function among Firefighters in South Korea: A Prospective before–after Study" International Journal of Environmental Research and Public Health 17, no. 13: 4647. https://doi.org/10.3390/ijerph17134647