Table 1. Age and age-standardized baseline characteristics of the study population at baseline by category of years spent in rotating night shift work.
| Characteristics | Duration of Rotating Night Shift Work | ||||
| Never | 1–2 y | 3–9 y | 10–19 y | ≥20 y | |
| NHS I (1988) | |||||
| n (%) | 28,367 (41.0) | 16,941 (24.5) | 16,146 (23.3) | 4,909 (7.1) | 2,906 (4.2) |
| Age (y) | 53.5 (7.1) | 53.1 (7.0) | 54.5 (7.1) | 54.7 (7.1) | 57.0 (6.4) |
| BMI (kg/m2) | 25.1 (4.6) | 25.0 (4.5) | 25.5 (4.8) | 26.3 (5.1) | 26.6 (5.5) |
| Physical activity (MET-h/wk) | 14.8 (21.2) | 15.9 (22.0) | 16.4 (22.8) | 16.0 (20.8) | 17.8 (27.6) |
| Alcohol (g/d) | 6.3 (10.7) | 6.6 (10.8) | 6.4 (10.7) | 5.9 (10.8) | 5.2 (10.3) |
| Total energy (kcal/d) | 1,749 (519) | 1,778 (516) | 1,788 (532) | 1,794 (538) | 1,783 (559) |
| Diabetes dietary score | 12.0 (2.4) | 12.1 (2.4) | 12.0 (2.4) | 11.8 (2.4) | 11.7 (2.4) |
| Cereal fiber (g/d) | 4.5 (3.1) | 4.6 (3.2) | 4.4 (2.9) | 4.3 (3.0) | 4.3 (3.5) |
| Glycemic load | 98.7 (18.8) | 98.9 (18.5) | 98.5 (18.6) | 98.6 (18.9) | 99.2 (19.3) |
| Polyunsaturated to saturated fat ratio | 0.6 (0.2) | 0.6 (0.2) | 0.6 (0.2) | 0.5 (0.2) | 0.5 (0.2) |
| Trans-fat (% of energy) | 1.7 (0.5) | 1.7 (0.5) | 1.7 (0.5) | 1.7 (0.5) | 1.7 (0.6) |
| Fruit and vegetables (servings/d) | 4.9 (2.0) | 5.0 (2.0) | 5.0 (2.0) | 5.0 (2.1) | 4.9 (2.1) |
| Coffee (cups/d) | 2.4 (1.7) | 2.4 (1.7) | 2.5 (1.7) | 2.7 (1.8) | 2.7 (1.9) |
| Red meat (servings/d) | 1.2 (0.6) | 1.2 (0.6) | 1.2 (0.6) | 1.3 (0.6) | 1.2 (0.6) |
| Soft drinks (servings/d) | 0.8 (1.0) | 0.8 (1.0) | 0.8 (1.1) | 0.9 (1.2) | 0.9 (1.2) |
| Race, white | 98 | 98 | 98 | 97 | 97 |
| Current smoker | 17 | 17 | 20 | 25 | 24 |
| Premenopausal | 39 | 39 | 38 | 37 | 36 |
| Current hormone therapy user | 21 | 22 | 21 | 19 | 17 |
| Regular aspirin user | 67 | 69 | 67 | 67 | 66 |
| Family history of diabetes | 27 | 28 | 30 | 31 | 32 |
| Hypertension | 24 | 23 | 26 | 28 | 29 |
| High cholesterol | 22 | 22 | 22 | 22 | 22 |
| Short sleep duration, ≤6 h/d | 23 | 24 | 27 | 33 | 35 |
| Regular snoring | 7 | 7 | 8 | 9 | 10 |
| NHS II (1989) | |||||
| n (%) | 41,084 (38.1) | 31,471 (29.2) | 30,546 (28.3) | 4,673 (4.3) | 141 (0.1) |
| Age (y) | 34.3 (4.7) | 34.1 (4.8) | 34.1 (4.6) | 36.7 (3.4) | 40.4 (2.5) |
| BMI (kg/m2) | 23.8 (4.8) | 23.7 (4.7) | 24.3 (5.2) | 25.3 (5.9) | 24.8 (5.6) |
| Physical activity (MET-h/wk) | 22.9 (34.2) | 25.2 (36.4) | 27.3 (40.0) | 28.2 (41.7) | 25.1 (54.9) |
| Alcohol (g/d) | 3.0 (6.0) | 3.2 (6.2) | 3.3 (6.1) | 3.0 (6.4) | 1.4 (4.5) |
| Total energy (kcal/d) | 1,769 (538) | 1,792 (546) | 1,803 (556) | 1,812 (573) | 1,803 (497) |
| Diabetes dietary score | 12.0 (2.7) | 12.1 (2.7) | 12.0 (2.7) | 11.8 (2.7) | 11.4 (2.4) |
| Cereal fiber (g/d) | 6.2 (2.5) | 6.2 (2.5) | 6.0 (2.4) | 5.8 (2.4) | 5.5 (2.2) |
| Glycemic load | 124.3 (18.9) | 124.0 (18.7) | 123.6 (18.8) | 123.7 (19.0) | 122.1 (18.5) |
| Polyunsaturated to saturated fat ratio | 0.54 (0.14) | 0.54 (0.14) | 0.53 (0.14) | 0.53 (0.14) | 0.50 (0.14) |
| Trans-fat (% of energy) | 1.6 (0.5) | 1.6 (0.5) | 1.6 (0.5) | 1.6 (0.5) | 1.6 (0.6) |
| Whole grain (g/d) | 23.4 (13.9) | 23.4 (13.7) | 23.0 (13.5) | 21.8 (13.0) | 21.4 (12.5) |
| Fruit and vegetables (servings/d) | 5.0 (2.5) | 5.2 (2.6) | 5.3 (2.7) | 5.3 (2.8) | 5.8 (2.9) |
| Coffee (cups/d) | 1.5 (1.5) | 1.6 (1.5) | 1.6 (1.5) | 1.6 (1.6) | 1.6 (1.7) |
| Red meat (servings/d) | 1.0 (0.6) | 1.0 (0.6) | 1.0 (0.6) | 1.0 (0.6) | 1.1 (0.6) |
| Soft drinks (servings/d) | 1.3 (1.2) | 1.4 (1.3) | 1.5 (1.3) | 1.6 (1.4) | 1.6 (1.5) |
| Race, white | 96 | 95 | 95 | 95 | 71a |
| Current smoker | 12 | 13 | 15 | 19 | 26 |
| Premenopausal | 97 | 97 | 97 | 96 | 96 |
| Current hormone therapy user | 3 | 4 | 4 | 5 | 3 |
| Current oral contraceptive user | 13 | 13 | 13 | 11 | 14 |
| Regular aspirin user | 11 | 11 | 11 | 14 | 7 |
| Family history of diabetes | 32 | 33 | 34 | 36 | 37 |
| Hypertension | 5 | 5 | 5 | 7 | 5 |
| High cholesterol | 10 | 10 | 10 | 11 | 7 |
Data were expressed as mean (SD) or percentage, unless otherwise specified. The number of missing data in NHS I: BMI (n = 4,825); physical activity level (n = 126); diet information (n = 14,612); smoking status (n = 145); menopausal status and hormone use (n = 3,229); sleep duration (n = 8,964); snoring frequency (n = 9,031). The number of missing data in NHS II: BMI (n = 252); physical activity level (n = 393); diet information (n = 19,496); smoking status (n = 473); menopausal status and hormone use (n = 649).
a
Because of small sample size in this category, the percentage might not be accurate. In 2001 for NHS II, the corresponding percentage was 95%.