Table 1.
Baseline characteristics for the 43 810 women included in the study separated by BC status*
| Characteristic | Total No. (%) | Breast cancer, No. (%) |
|
|---|---|---|---|
| No | Yes | ||
| No. of women | 43 810 | 43 247 | 563 |
| No. of screening examinations | |||
| 2 rounds | 10 014 (22.8) | 9675 (22.3) | 339 (60.2) |
| ≥3 rounds | 33 796 (77.1) | 33 572 (77.6) | 224 (39.7) |
| Age at baseline, mean (SD), y | 53.7 (9.4) | 53.6 (9.4) | 57.3 (9.4) |
| Menopausal status | |||
| Pre | 20 718 (47.2) | 20 518 (47.4) | 200 (35.5) |
| Post | 23 092 (52.7) | 22 729 (52.55) | 363 (64.4) |
| BMI, mean (SD), kg/m2 | 25.1 (4.1) | 25.1 (4.1) | 25.5 (4.1) |
| BMI, kg/m2 | |||
| <20 | 2382 (5.4) | 2347 (5.4) | 35 (6.2) |
| 20–24.9 | 22 298 (50.8) | 22 045 (50.9) | 253 (44.9) |
| 25–29.9 | 13 805 (31.5) | 13 603 (31.4) | 202 (35.8) |
| ≥30 | 5325 (12.1) | 5252 (12.1) | 73 (12.9) |
| Smoking status | |||
| Never | 21 074 (48.1) | 20 826 (48.1) | 248 (44.0) |
| Former | 17 234 (39.3) | 16 990 (39.2) | 244 (43.3) |
| Current | 5128 (11.7) | 5060 (11.7) | 68 (12.0) |
| Missing | 374 (0.8) | 371 (0.8) | 3 (0.5) |
| Alcohol consumption, g/d, mean (SD), g/d | 7.1 (8.5) | 7.1 (8.5) | 7.4 (8.2) |
| Alcohol consumption, g/d | |||
| 0 | 7957 (18.1) | 7861 (18.1) | 96 (17.0) |
| 0.1–10 | 26 935 (61.4) | 26 584 (61.4) | 351 (62.3) |
| >10 | 8192 (18.6) | 8084 (18.6) | 108 (19.1) |
| Missing | 726 (1.6) | 718 (1.6) | 8 (1.4) |
| Physical activity, MET-h/d, mean (SD), MET-h/d | 42.5 (6.2) | 42.5 (6.2) | 41.9 (5.6) |
| Physical activity, MET-h/d | |||
| <40 | 15 263 (34.8) | 15 068 (34.8) | 195 (34.6) |
| 40.0–44.9 | 15 245 (34.7) | 15 032 (34.7) | 213 (37.8) |
| 45.0–49.9 | 7769 (17.7) | 7667 (17.7) | 102 (18.1) |
| ≥50.0 | 4305 (9.8) | 4268 (9.8) | 37 (6.5) |
| Missing | 1228 (2.8) | 1212 (2.8) | 16 (2.8) |
| Age at first birth, mean (SD), y | 27.3 (5.2) | 27.3 (5.2) | 27.0 (5.0) |
| Age at first birth, y | |||
| <25 | 12 081 (27.5) | 11 931 (27.5) | 150 (26.6) |
| 25–29.9 | 13 547 (30.9) | 13 363 (30.8) | 184 (32.6) |
| ≥30 | 12 348 (28.1) | 12 198 (28.2) | 150 (26.6) |
| Missing | 5834 (13.3) | 5755 (13.3) | 79 (14.0) |
| No. of births, mean (SD) | 1.9 (1.0) | 1.9 (1.0) | 1.8 (1.0) |
| No. of births | |||
| 0 | 5416 (12.3) | 6101 (14.1) | 75 (13.3) |
| 1–2 | 27 249 (62.1) | 20 792 (48.0) | 356 (63.2) |
| ≥3 | 10 743 (24.5) | 8582 (19.8) | 128 (22.7) |
| Missing | 402 (1.0) | 398 (0.9) | 4 (0.7) |
| Breast-feeding duration, mean (SD), mo | 18.8 (10.0) | 18.9 (10.0) | 17.4 (9.4) |
| Duration of breast-feeding, mo | |||
| <6 | 1780 (4.0) | 1748 (4.0) | 32 (5.6) |
| 6–12 | 5201 (11.8) | 5121 (11.8) | 80 (14.2) |
| >12 | 28 218 (64.4) | 27 873 (64.4) | 345 (61.2) |
| Missing | 2510 (5.7) | 2485 (5.7) | 25 (4.4) |
| Time since last birth, mean (SD), y | 22.0 (11.8) | 21.9 (11.8) | 26.3 (11.8) |
| Time since last birth, y | |||
| <10 | 6751 (15.4) | 6703 (15.4) | 48 (8.5) |
| ≥10 | 31 531 (71.9) | 31 093 (71.8) | 438 (77.7) |
| Missing | 5528 (12.6) | 5451 (12.6) | 77 (13.6) |
| Age at menarche, mean (SD), y | 13.0 (1.4) | 13.0 (1.4) | 13.1 (1.4) |
| Age at menarche, y | |||
| <13 | 14 840 (33.8) | 14 666 (33.9) | 174 (30.9) |
| ≥13 | 27 842 (63.5) | 27 470 (63.5) | 372 (66.0) |
| Missing | 1128 (2.5) | 1111 (1.4) | 17 (3.0) |
| Contraceptive use | |||
| Never | 5923 (13.5) | 5824 (13.4) | 99 (17.5) |
| Ever | 37 055 (84.5) | 36 598 (84.6) | 457 (81.1) |
| Missing | 832 (1.8) | 825 (1.9) | 7 (1.2) |
| MHT | |||
| Never user | 33 390 (76.2) | 32 999 (76.3) | 391 (69.4) |
| Former user | 5734 (13.0) | 5638 (13.0) | 96 (17.0) |
| Current user | 1483 (3.3) | 1448 (3.3) | 35 (6.2) |
| Missing | 3203 (7.3) | 3162 (7.3) | 41 (7.2) |
| Family history of BC | |||
| No | 36 755 (83.8) | 36 332 (84.0) | 423 (75.1) |
| Yes | 5883 (13.4) | 5758 (13.3) | 125 (22.2) |
| Missing | 1172 (2.6) | 1157 (2.6) | 15 (2.6) |
*BC = breast cancer;: BMI = body mass index; MET = metabolic equivalent of task; MHT = menopausal hormone therapy.