Table 1

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.