Distribution of potential and established risk factors for breast cancer among cases and white-collar workers and blue-collar workers
| All (%) | Breast cancer* (%) | χ2 test† | White collar‡ | Blue collar§ | χ2 test¶ | |
| n=14 119 | n=897 | n=9860 | n=4194 | |||
| Age** (years) | p=<0.001 | p=<0.001 | ||||
| 45–49 | 3331 (23.6) | 180 (20.1) | 2581 (26.2) | 746 (17.8) | ||
| 50–54 | 2681 (19.0) | 204 (22.7) | 1967 (20.0) | 709 (16.9) | ||
| 55–59 | 2419 (17.1) | 197 (22.0) | 1669 (16.9) | 740 (17.6) | ||
| 60–64 | 2758 (19.5) | 168 (18.7) | 1781 (18.1) | 953 (22.7) | ||
| 65–69 | 1606 (11.4) | 87 (9.7) | 1021 (10.4) | 570 (13.6) | ||
| 70–74 | 1324 (9.4) | 61 (6.8) | 841 (8.5) | 476 (11.4) | ||
| Parity | p=0.04 | p=<0.001 | ||||
| 0 | 1896 (13.7) | 132 (15.1) | 1456 (15.1) | 435 (10.5) | ||
| 1 | 3065 (22.1) | 172 (19.7) | 2173 (22.5) | 884 (21.3) | ||
| 2 | 5802 (41.8) | 393 (44.9) | 4100 (42.5) | 1674 (40.3) | ||
| 3 | 2275 (16.4) | 140 (16.0) | 1468 (15.2) | 789 (19.0) | ||
| ≥4 | 831 (6.0) | 38 (4.3) | 457 (4.7) | 368 (8.9) | ||
| Age at first child (years) | p=0.42 | p=<0.001 | ||||
| <20 | 1457 (10.5) | 83 (9.5) | 870 (9.0) | 580 (14.0) | ||
| 20–24 | 4683 (33.8) | 301 (34.4) | 3038 (31.5) | 1621 (39.1) | ||
| 25–29 | 4056 (29.3) | 240 (27.5) | 2963 (30.7) | 1073 (25.9) | ||
| 30–34 | 1341 (9.7) | 85 (9.7) | 994 (10.3) | 339 (8.2) | ||
| 35+ | 426 (3.1) | 33 (3.8) | 328 (3.4) | 97 (2.3) | ||
| No children | 1896 (13.7) | 132 (15.1) | 1456 (15.1) | 435 (10.5) | ||
| Months of breast feeding/child | p=0.08 | p=<0.001 | ||||
| 0 | 562 (4.2) | 29 (3.5) | 383 (4.1) | 177 (4.5) | ||
| 1–5 | 7283 (54.3) | 426 (50.7) | 4974 (53.2) | 2267 (57.0) | ||
| 6–12 | 3520 (26.3) | 240 (28.6) | 2451 (26.2) | 1048 (26.3) | ||
| ≥13 | 146 (1.1) | 13 (1.6) | 93 (1.0) | 52 (1.3) | ||
| No children | 1896 (14.1) | 132 (15.7) | 1456 (15.5) | 435 (10.9) | ||
| Hormone replacement therapy | p=<0.001 | p=<0.001 | ||||
| No treatment | 11 481 (81.5) | 650 (72.7) | 7825 (79.6) | 3599 (85.9) | ||
| Oestrogen | 921 (6.5) | 58 (6.5) | 702 (7.1) | 213 (5.1) | ||
| Progesterone | 79 (0.6) | 9 (1.0) | 63 (0.6) | 16 (0.4) | ||
| Oestrogen+progesterone | 1599 (11.4) | 177 (19.8) | 1237 (12.6) | 360 (8.6) | ||
| Physical activity (percentile) | p=0.04 | p=<0.001 | ||||
| 0–25 | 3420 (24.4) | 228 (25.5) | 2249 (22.9) | 1158 (27.8) | ||
| 25–50 | 3466 (24.7) | 250 (27.9) | 2468 (25.1) | 984 (23.6) | ||
| 50–75 | 3630 (25.9) | 210 (23.5) | 2615 (26.6) | 999 (24.0) | ||
| 75–100 | 3529 (25.1) | 207 (23.1) | 2485 (25.3) | 1022 (24.6) | ||
| Alcohol (g/day) | p=<0.001 | p=<0.001 | ||||
| 0 | 1012 (7.2) | 42 (4.7) | 504 (5.1) | 501 (12.0) | ||
| 1–14 | 10 799 (76.6) | 692 (77.2) | 7460 (75.7) | 3289 (78.6) | ||
| 15–30 | 1969 (14.0) | 121 (13.5) | 1627 (16.5) | 335 (8.0) | ||
| >30 | 327 (2.3) | 42 (4.7) | 267 (2.7) | 59 (1.4) | ||
| Height (cm) | p=0.04 | p=<0.001 | ||||
| <160 | 3445 (24.4) | 187 (20.9) | 2087 (21.2) | 1339 (32.0) | ||
| 160–169 | 8351 (59.2) | 559 (62.3) | 5909 (60.0) | 2400 (57.3) | ||
| ≥170 | 2305 (16.4) | 151 (16.8) | 1852 (18.8) | 449 (10.7) | ||
| Body mass index (kg/m2) | p=0.03 | p=<0.001 | ||||
| <18.5, underweight | 206 (1.5) | 10 (1.1) | 162 (1.5) | 43 (1.0) | ||
| 18.5–24.9, normal weight | 7272 (51.6) | 424 (47.3) | 5520 (56.1) | 1724 (41.2) | ||
| 25–29.9, overweight | 4703 (33.4) | 321 (35.8) | 3057 (31.0) | 1624 (38.8) | ||
| ≥30, obese | 1920 (13.6) | 142 (15.8) | 1109 (11.3) | 797 (19.0) |
*Incident invasive breast cancer International Classification of Diseases, Seventh Revision =170.
†χ2 test comparing the distribution in the total sample and among all breast cancer cases.
‡White-collar workers: professional, administrative, bookkeeping and sales work.
§Blue-collar workers: agricultural, mining, transportation, production, service work and armed forces.
¶ χ2 test comparing the distribution among blue-collar workers and white-collar workers.
** Age at baseline.