Table 2. Hazard ratio of type 2 diabetes by years of working rotating night shifts.
| Studies | Duration of Rotating Night Shift Work | p-Value for Trend | Hazard Ratio per 5 y of Shift Work | ||||
| Never | 1–2 y | 3–9 y | 10–19 y | ≥20 y | |||
| NHS I (1988–2008) | |||||||
| Cases/person-years | 2,322/519,988 | 1,388/311,468 | 1,534/292,014 | 549/86,844 | 372/50,380 | — | — |
| Incidence rate (per 1,000 person-years) | 4.5 | 4.5 | 5.3 | 6.3 | 7.4 | — | — |
| Age-adjusted model | 1.00 | 0.99 (0.93–1.06) | 1.17 (1.10–1.25) | 1.42 (1.29–1.55) | 1.64 (1.46–1.83) | <0.001 | 1.14 (1.12–1.17) |
| Multivariate-adjusted model 1 | 1.00 | 1.01 (0.95–1.08) | 1.15 (1.08–1.23) | 1.32 (1.20–1.45) | 1.47 (1.32–1.64) | <0.001 | 1.11 (1.08–1.13) |
| Multivariate-adjusted model 2 | 1.00 | 1.00 (0.94–1.07) | 1.06 (0.99–1.13) | 1.09 (0.99–1.20) | 1.20 (1.07–1.34) | <0.001 | 1.05 (1.02–1.07) |
| NHS II (1989–2007) | |||||||
| Cases/person-years | 1,000/584,808 | 1,053/540,270 | 1,377/599,813 | 449/128,835 | 82/11,593 | — | — |
| Incidence rate (per 1,000 person-years) | 1.7 | 2.0 | 2.3 | 3.5 | 7.1 | — | — |
| Age-adjusted model | 1.00 | 1.13 (1.04–1.23) | 1.34 (1.23–1.45) | 1.76 (1.57–1.96) | 2.50 (2.00–3.14) | <0.001 | 1.23 (1.19–1.27) |
| Multivariate-adjusted model 1 | 1.00 | 1.12 (1.02–1.22) | 1.28 (1.18–1.39) | 1.54 (1.38–1.73) | 2.13 (1.70–2.67) | <0.001 | 1.18 (1.14–1.22) |
| Multivariate-adjusted model 2 | 1.00 | 1.07 (0.98–1.16) | 1.05 (0.97–1.14) | 1.11 (1.00–1.25) | 1.44 (1.15–1.80) | 0.026 | 1.05 (1.01–1.08) |
| Pooled results a | |||||||
| Age-adjusted model | 1.00 | 1.04 (0.99–1.10) | 1.24 (1.18–1.30) | 1.55 (1.45–1.66) | 1.78 (1.61–1.96) | <0.001 | 1.17 (1.15–1.20) |
| Multivariate-adjusted model 1 | 1.00 | 1.05 (1.00–1.11) | 1.20 (1.14–1.26) | 1.40 (1.30–1.51) | 1.58 (1.43–1.74) | <0.001 | 1.13 (1.11–1.14) |
| Multivariate-adjusted model 2 | 1.00 | 1.03 (0.98–1.08) | 1.06 (1.00–1.11) | 1.10 (1.02–1.18) | 1.24 (1.13–1.37) | <0.001 | 1.05 (1.04–1.06) |
Multivariate-adjusted model 1: adjusted for age (continuous), alcohol consumption (0, 0.1–4.9, 5.0–14.9, ≥15 g/d), physical activity level (<3, 3–8.9, 9–17.9, 18–26.9, ≥27 MET-h/wk), smoking status (never, past, current 1–14/d, current 15–24/d, current ≥25/d), race (white, nonwhite), menopausal status and hormone use (premenopausal, postmenopausal never users, postmenopausal past users, postmenopausal current users), oral contraceptive use (yes, no; in NHS II), family history of diabetes (yes, no), current aspirin use (yes, no), quintiles of total calorie, diabetes dietary score. Multivariate-adjusted model 2: model 1 plus updated BMI category (<23, 23–24.9, 25–29.9, 30–34.9, ≥35 kg/m2).
a
The results were pooled using fixed-effect models.