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1Department of Occupational and Environmental Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea
2Department of Occupational and Environmental Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea
© 2022, Korean Society of Epidemiology
This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
DATA AVAILABILITY
The data are not available to be shared publicly, because we do not have permission from the institutional review board to distribute the data. However, data can be available from the Kangbuk Samsung Health Study upon reasonable request, whose authors may be contacted through the corresponding author of this manuscript.
CONFLICT OF INTEREST
The authors have no conflicts of interest to declare for this study.
FUNDING
None.
AUTHOR CONTRIBUTIONS
Conceptualization: Lee Y. Formal analysis: Lee Y, Lee W, Kim HR. Funding acquisition: None. Methodology: Lee Y, Kim HR. Writing – original draft: Lee Y. Writing – review & editing: Lee Y, Lee W, Kim HR.
Characteristics | Overall |
Weekly working hours |
p-value for trend | |||
---|---|---|---|---|---|---|
36-40 | 41-52 | 53-60 | >60 | |||
Total (n) | 45,259 | 15,139 | 26,327 | 2,545 | 1,248 | |
Age (yr) | 37.6±8.1 | 40.6±8.9 | 36.0±7.1 | 37.4±7.6 | 37.1±8.5 | <0.001 |
Men | 69.8 | 52.4 | 78.0 | 82.2 | 82.6 | <0.001 |
Current smoker | 22.5 | 19.0 | 22.9 | 32.3 | 35.5 | <0.001 |
Alcohol heavy intake1 | 17.0 | 17.8 | 15.9 | 21.0 | 22.0 | 0.419 |
Hypertension | 11.3 | 13.0 | 10.2 | 13.4 | 10.6 | <0.001 |
Diabetes mellitus | 3.6 | 5.0 | 2.8 | 3.4 | 3.8 | <0.001 |
Cardiovascular disease | 1.0 | 1.5 | 0.8 | 0.9 | 1.4 | 0.003 |
Obesity2 | 31.7 | 27.7 | 32.9 | 38.6 | 38.5 | <0.001 |
BMI (kg/m2) | 23.7±3.3 | 23.2±3.3 | 23.8±3.3 | 24.3±3.4 | 24.4±3.5 | <0.001 |
Systolic BP (mmHg) | 109.5±12.7 | 107.7±13.4 | 110.2±12.3 | 111.4±12.5 | 111.3±12.3 | <0.001 |
Diastolic BP (mmHg) | 70.8±10.1 | 70.2±10.6 | 71.1±9.8 | 71.9±10.1 | 71.2±9.6 | <0.001 |
Glucose (mg/dL) | 93 (88-99) | 93 (88-100) | 93 (88-99) | 94 (88-99) | 94 (89-100) | 0.001 |
TSH (μIU/mL) | 2.01±0.97 | 2.01±0.97 | 2.01±0.97 | 1.97±0.98 | 1.98±0.99 | 0.045 |
free T4 (ng/dL) | 1.30±0.16 | 1.27±0.15 | 1.32±0.15 | 1.31±0.16 | 1.30±0.16 | <0.001 |
Daytime work3 | 89.9 | 91.8 | 89.5 | 88.7 | 76.5 | <0.001 |
Values are presented as mean±standard deviation, percentage, or median (interquartile range).
BMI, body mass index; BP, blood pressure; TSH, thyroid-stimulating hormone.
1 Women: ≥20 g/day, men: ≥30 g/day.
2 BMI ≥25kg/m2.
3 Participants who answered “I work mostly during the day (between 6 a.m. and 6 p.m.)”.
Variables | PY | Incident cases | Incidence density (per 102 PY) (95% CI) | Age- and sex-adjusted |
Multivariable-adjusted1 |
|||
---|---|---|---|---|---|---|---|---|
Model 1 | Model 2 | Model 3 | ||||||
Weekly working hours | ||||||||
36-40 | 46,576.5 | 1,084 | 2.32 (2.19, 2.47) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |
41-52 | 82,653.6 | 1,484 | 1.80 (1.71, 1.89) | 1.10 (1.01, 1.20) | 1.12 (1.02, 1.22) | 1.12 (1.02, 1.23) | 1.13 (1.03, 1.24) | |
53-60 | 5,992.5 | 228 | 3.80 (3.34, 4.33) | 2.44 (2.11, 2.83) | 2.50 (2.15, 2.91) | 2.51 (2.15, 2.92) | 2.53 (2.17, 2.95) | |
>60 | 3,039.1 | 118 | 3.88 (3.24, 4.65) | 2.42 (1.99, 2.93) | 2.57 (2.10, 3.14) | 2.56 (2.09, 3.12) | 2.57 (2.09, 3.15) | |
Per 1 hour | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | ||||
p for trend | <0.001 | <0.001 | <0.001 | <0.001 | ||||
Age | 1.04 (1.03, 1.04) | 1.04 (1.03, 1.05) | 1.04 (1.04, 1.05) | 1.04 (1.04, 1.05) | ||||
Sex | ||||||||
Men | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | ||||
Women | 1.81 (1.67, 1.97) | 1.71 (1.56, 1.88) | 1.75 (1.58, 1.93) | 1.73 (1.57, 1.91) | ||||
Alcohol intake | ||||||||
Not heavy drinking | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |||||
Heavy drinking | 1.05 (0.95, 1.17) | 1.05 (0.95, 1.17) | 1.05 (0.94, 1.17) | |||||
Smoking status | ||||||||
Not current smoker | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |||||
Current smoker | 0.82 (0.74, 0.91) | 0.82 (0.74, 0.91) | 0.81 (0.73, 0.90) | |||||
DM | 0.79 (0.63, 0.98) | 0.78 (0.62, 0.98) | ||||||
Hypertension | 0.98 (0.86, 1.12) | 0.97 (0.85, 1.10) | ||||||
Cardiovascular disease | 1.05 (0.73, 1.51) | 1.01 (0.70, 1.46) | ||||||
BMI | 1.01 (1.00, 1.02) | 1.01 (0.99, 1.02) | ||||||
Shift work schedule | ||||||||
Daytime work | 1.00 (reference) | |||||||
Shift work | 1.25 (1.10, 1.42) |
Values are presented as hazard ratio (95% CI).
PY, person-years; CI, confidence interval; DM, diabetes mellitus; BMI, body mass index.
1 Estimated from Cox proportional hazard models; Model 1 was adjusted for age, sex, alcohol intake, and smoking status; Model 2: model 1 plus adjustment for hypertension, DM, cardiovascular disease, and BMI; Model 3: model 2 plus adjustment for shift work.
Characteristics | Overall | Weekly working hours |
p-value for trend | |||
---|---|---|---|---|---|---|
36-40 | 41-52 | 53-60 | >60 | |||
Total (n) | 45,259 | 15,139 | 26,327 | 2,545 | 1,248 | |
Age (yr) | 37.6±8.1 | 40.6±8.9 | 36.0±7.1 | 37.4±7.6 | 37.1±8.5 | <0.001 |
Men | 69.8 | 52.4 | 78.0 | 82.2 | 82.6 | <0.001 |
Current smoker | 22.5 | 19.0 | 22.9 | 32.3 | 35.5 | <0.001 |
Alcohol heavy intake |
17.0 | 17.8 | 15.9 | 21.0 | 22.0 | 0.419 |
Hypertension | 11.3 | 13.0 | 10.2 | 13.4 | 10.6 | <0.001 |
Diabetes mellitus | 3.6 | 5.0 | 2.8 | 3.4 | 3.8 | <0.001 |
Cardiovascular disease | 1.0 | 1.5 | 0.8 | 0.9 | 1.4 | 0.003 |
Obesity |
31.7 | 27.7 | 32.9 | 38.6 | 38.5 | <0.001 |
BMI (kg/m2) | 23.7±3.3 | 23.2±3.3 | 23.8±3.3 | 24.3±3.4 | 24.4±3.5 | <0.001 |
Systolic BP (mmHg) | 109.5±12.7 | 107.7±13.4 | 110.2±12.3 | 111.4±12.5 | 111.3±12.3 | <0.001 |
Diastolic BP (mmHg) | 70.8±10.1 | 70.2±10.6 | 71.1±9.8 | 71.9±10.1 | 71.2±9.6 | <0.001 |
Glucose (mg/dL) | 93 (88-99) | 93 (88-100) | 93 (88-99) | 94 (88-99) | 94 (89-100) | 0.001 |
TSH (μIU/mL) | 2.01±0.97 | 2.01±0.97 | 2.01±0.97 | 1.97±0.98 | 1.98±0.99 | 0.045 |
free T4 (ng/dL) | 1.30±0.16 | 1.27±0.15 | 1.32±0.15 | 1.31±0.16 | 1.30±0.16 | <0.001 |
Daytime work |
89.9 | 91.8 | 89.5 | 88.7 | 76.5 | <0.001 |
Variables | PY | Incident cases | Incidence density (per 102 PY) (95% CI) | Age- and sex-adjusted | Multivariable-adjusted |
|||
---|---|---|---|---|---|---|---|---|
Model 1 | Model 2 | Model 3 | ||||||
Weekly working hours | ||||||||
36-40 | 46,576.5 | 1,084 | 2.32 (2.19, 2.47) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |
41-52 | 82,653.6 | 1,484 | 1.80 (1.71, 1.89) | 1.10 (1.01, 1.20) | 1.12 (1.02, 1.22) | 1.12 (1.02, 1.23) | 1.13 (1.03, 1.24) | |
53-60 | 5,992.5 | 228 | 3.80 (3.34, 4.33) | 2.44 (2.11, 2.83) | 2.50 (2.15, 2.91) | 2.51 (2.15, 2.92) | 2.53 (2.17, 2.95) | |
>60 | 3,039.1 | 118 | 3.88 (3.24, 4.65) | 2.42 (1.99, 2.93) | 2.57 (2.10, 3.14) | 2.56 (2.09, 3.12) | 2.57 (2.09, 3.15) | |
Per 1 hour | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | 1.02 (1.02, 1.03) | ||||
p for trend | <0.001 | <0.001 | <0.001 | <0.001 | ||||
Age | 1.04 (1.03, 1.04) | 1.04 (1.03, 1.05) | 1.04 (1.04, 1.05) | 1.04 (1.04, 1.05) | ||||
Sex | ||||||||
Men | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | ||||
Women | 1.81 (1.67, 1.97) | 1.71 (1.56, 1.88) | 1.75 (1.58, 1.93) | 1.73 (1.57, 1.91) | ||||
Alcohol intake | ||||||||
Not heavy drinking | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |||||
Heavy drinking | 1.05 (0.95, 1.17) | 1.05 (0.95, 1.17) | 1.05 (0.94, 1.17) | |||||
Smoking status | ||||||||
Not current smoker | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | |||||
Current smoker | 0.82 (0.74, 0.91) | 0.82 (0.74, 0.91) | 0.81 (0.73, 0.90) | |||||
DM | 0.79 (0.63, 0.98) | 0.78 (0.62, 0.98) | ||||||
Hypertension | 0.98 (0.86, 1.12) | 0.97 (0.85, 1.10) | ||||||
Cardiovascular disease | 1.05 (0.73, 1.51) | 1.01 (0.70, 1.46) | ||||||
BMI | 1.01 (1.00, 1.02) | 1.01 (0.99, 1.02) | ||||||
Shift work schedule | ||||||||
Daytime work | 1.00 (reference) | |||||||
Shift work | 1.25 (1.10, 1.42) |
Subgroup | Weekly working hours |
p for trend | p for interaction | ||||
---|---|---|---|---|---|---|---|
36-40 | 41-52 | 53-60 | >60 | ||||
Age (yr) | 0.009 | ||||||
<36 (n=21,659) | 1.00 (reference) | 0.98 (0.83, 1.14) | 2.21 (1.69, 2.89) | 2.32 (1.64, 3.28) | <0.001 | ||
≥36 (n=23,600) | 1.00 (reference) | 1.17 (1.04, 1.31) | 2.65 (2.19, 3.19) | 2.73 (2.12, 3.52) | <0.001 | ||
Sex | 0.009 | ||||||
Women (n=13,667) | 1.00 (reference) | 1.06 (0.92, 1.22) | 1.77 (1.27, 2.48) | 1.65 (1.02, 2.69) | 0.004 | ||
Men (n=31,592) | 1.00 (reference) | 1.22 (1.08, 1.38) | 2.93 (2.44, 3.52) | 3.06 (2.42, 3.87) | <0.001 | ||
Body mass index (kg/m2) | 0.259 | ||||||
<25 (n=30,903) | 1.00 (reference) | 1.10 (0.99, 1.23) | 2.31 (1.90, 2.81) | 2.40 (1.84, 3.13) | <0.001 | ||
≥25 (n=14,323) | 1.00 (reference) | 1.21 (1.01, 1.44) | 2.97 (2.29, 3.85) | 2.93 (2.11, 4.07) | <0.001 | ||
Shift work schedule | 0.025 | ||||||
Daytime work (n=40,674) | 1.00 (reference) | 1.13 (1.02, 1.24) | 2.57 (2.19, 3.02) | 2.93 (2.35, 3.66) | <0.001 | ||
Shift work (n=4,238) | 1.00 (reference) | 1.06 (0.79, 1.41) | 2.09 (1.23, 3.56) | 1.36 (0.79, 2.35) | 0.070 |
Values are presented as mean±standard deviation, percentage, or median (interquartile range). BMI, body mass index; BP, blood pressure; TSH, thyroid-stimulating hormone. Women: ≥20 g/day, men: ≥30 g/day. BMI ≥25kg/m2. Participants who answered “I work mostly during the day (between 6 a.m. and 6 p.m.)”.
Values are presented as hazard ratio (95% CI). PY, person-years; CI, confidence interval; DM, diabetes mellitus; BMI, body mass index. Estimated from Cox proportional hazard models; Model 1 was adjusted for age, sex, alcohol intake, and smoking status; Model 2: model 1 plus adjustment for hypertension, DM, cardiovascular disease, and BMI; Model 3: model 2 plus adjustment for shift work.
Estimated from Cox proportional hazard models adjusted for age, sex, alcohol intake, smoking status, hypertension, diabetes mellitus, cardiovascular disease, body mass index, and shift work.