TABLE 1.
Characteristics of 53 273 women included in the final analyses, stratified by menopausal status
| Characteristics | Total | Premenopausal women | Postmenopausal women | P‐value* |
|---|---|---|---|---|
| No. of women (%) | 53 273 | 24 537 (46.0) | 28 736 (53.9) | |
| Mean age at baseline (SD) | 54.1 (9.7) | 45.4 (4.2) | 61.5 (6.6) | <.001 |
| Microcalcification clusters (%) | ||||
| 0 | 44 088 (82.7) | 21 595 (88.0) | 22 493 (78.2) | |
| ≥1 | 9167 (17.2) | 2934 (11.9) | 6233 (21.6) | |
| <.001 | ||||
| Missing | 18 (0.03) | |||
| Microcalcification clusters asymmetry (%) | ||||
| 0 | 44 793 (84.0) | 1866 (7.6) | 22 493 (91.6) | |
| ≥1 | 8462 (15.8) | 580 (2.3) | 6233 (21.6) | |
| 0.02 | ||||
| Missing | 18 (0.03) | |||
| Mean mammographic dense area (cm2) at baseline (SD) | 28.3 (23.8) | 37.1 (25.2) | 20.9 (19.6) | <.001 |
| Mammographic dense area (cm2) at baseline (%) | ||||
| <9.0 | 12 443 (23.3) | 2932 (11.9) | 9511 (33.0) | |
| 9.0‐19.9 | 10 943 (20.5) | 3603 (14.6) | 7340 (25.5) | |
| 20.0‐40.0 | 15 748 (29.5) | 8261 (33.6) | 7487 (26.0) | |
| >40 | 13 607 (25.5) | 9526 (38.8) | 4081 (14.2) | |
| <.001 | ||||
| Missing | 532 (0.9) | |||
| Mean BMI (kg/m2) (SD) | 25.1 (4.1) | 25.3 (4.0) | 24.9 (4.2) | <.001 |
| BMI (kg/m2) (%) | ||||
| 20‐24.9 | 27 123 (50.9) | 13 123 (53.4) | 14 000 (48.7) | |
| 25‐29.9 | 16 763 (31.4) | 6964 (28.3) | 9799 (34.1) | |
| ≥30 | 6460 (12.1) | 2935 (11.9) | 3525 (12.2) | |
| <.001 | ||||
| Smoking status (%) | ||||
| Never | 25 386 (47.6) | 13 558 (55.2) | 11 828 (41.6) | |
| Former | 20 912 (39.2) | 7977 (32.5) | 12 935 (45.0) | |
| Current | 6236 (11.7) | 2714 (11.0) | 3522 (12.2) | |
| <.001 | ||||
| Missing | 739 (1.3) | |||
| Mean alcohol consumption (gram/day) (SD) | 7.1 (8.5) | 7.9 (8.0) | 9.5 (9.2) | <.001 |
| Alcohol consumption (gram/day) (%) | ||||
| 0 | 9742 (18.2) | 4573 (18.6) | 5169 (17.9) | |
| 0.1‐10 | 32 426 (60.8) | 15 606 (63.0) | 16 820 (58.5) | |
| >10 | 9865 (18.5) | 3905 (15.9) | 5960 (20.7) | |
| <.001 | ||||
| Missing | 1240 (2.3) | |||
| Mean physical activity, (MET‐h per day) (SD) | 42.4 (6.2) | 43.1 (6.6) | 41.8 (5.8) | <.001 |
| Physical activity (MET‐h per day) (%) | ||||
| <40 | 18 492 (34.7) | 7811 (31.8) | 10 681 (37.1) | |
| 40.0‐44.9 | 18 326 (34.4) | 8113 (33.0) | 10 213 (35.5) | |
| 45.0‐49.9 | 9320 (17.4) | 4910 (20.0) | 4410 (15.3) | |
| ≥50.0 | 5114 (9.5) | 2944 (12.0) | 2170 (7.5) | |
| <.001 | ||||
| Missing | 2021 (3.7) | |||
| Mean age at first birth (SD) | 27.7 (5.2) | 28.7 (5.1) | 25.9 (5.0) | <.001 |
| Age at first birth (%) | ||||
| <20.0 | 2450 (4.5) | 497 (2.0) | 1953 (6.7) | |
| 20.0‐25.0 | 15 856 (29.7) | 5456 (22.2) | 10 400 (36.1) | |
| >25.0 | 27 505 (51.6) | 15 214 (62.0) | 12 291 (42.7) | |
| <.001 | ||||
| Missing | 7462 (14.0) | |||
| Mean number of births (SD) | 1.9 (1.0) | 2.1 (0.7) | 2.2 (0.8) | <.001 |
| Number of births (%) | ||||
| 0 | 6644 (12.4) | 3354 (13.6) | 4162 (14.4) | |
| 1‐2 | 32 824 (61.6) | 12 189 (49.6) | 13 119 (45.6) | |
| >2 | 13 012 (24.4) | 4629 (18.8) | 5815 (20.2) | |
| <.001 | ||||
| Missing | 793 (1.4) | |||
| Mean breast‐feeding duration (months) (SD) | 18.8 (10.0) | 20.6 (9.7) | 18.1 (9.6) | <.001 |
| Duration of breast‐feeding (months) (%) | ||||
| 0 | 911 (1.7) | 222 (0.9) | 689 (2.3) | |
| 1‐5 | 1214 (2.2) | 327 (1.3) | 887 (3.0) | |
| 6‐12 | 6558 (12.3) | 2168 (8.8) | 4390 (15.2) | |
| >12 | 33 830 (63.5) | 16 212 (66.0) | 17 618 (61.3) | |
| <.001 | ||||
| Missing | 9478 (17.7) | |||
| Mean time since last birth (years) (SD) | 22.5 (12.1) | 12.7 (6.6) | 30.9 (8.9) | <.001 |
| Time since last birth (years) (%) | ||||
| <10 | 7926 (14.8) | 7695 (31.3) | 231 (0.8) | |
| ≥10 | 38 444 (72.1) | 13 656 (55.6) | 24 788 (86.2) | |
| <.001 | ||||
| Missing | 6110 (11.4) | |||
| Mean age at menarche (SD) | 13.1 (1.4) | 12.9 (1.4) | 13.2 (1.4) | <.001 |
| Age at menarche (%) | ||||
| <13 | 17 782 (33.3) | 9109 (37.1) | 8673 (30.1) | |
| ≥13 | 33 876 (63.5) | 14 776 (60.2) | 19 100 (66.4) | |
| <.001 | ||||
| Missing | 1615 (3.0) | |||
| Oral contraceptives use (%) | ||||
| Never | 7512 (14.1) | 2142 (8.7) | 5370 (18.6) | |
| Ever | 44 441 (83.4) | 22 114 (90.1) | 22 327 (77.6) | |
| <.001 | ||||
| Missing | 1320 (2.4) | |||
| MTH use (%) | ||||
| Never user | 39 960 (75.0) | 22 410 (91.3) | 17 550 (61.0) | |
| Former user | 7373 (13.8) | 779 (3.1) | 6594 (22.9) | |
| Current user | 1879 (3.5) | 355 (1.4) | 1524 (5.3) | |
| <.001 | ||||
| Missing | 4061 (7.6) | |||
| Family history of breast cancer (%) | ||||
| No | 44 422 (83.3) | 20 844 (84.9) | 23 578 (82.0) | |
| Yes | 7211 (13.5) | 2989 (12.1) | 4222 (14.6) | |
| <.001 | ||||
| Missing | 1640 (3.0) | |||
| No of women with a PRS (%) | 7387 | 3505 (47.4) | 3882 (52.5) | |
Note: The number of women should be added to the number of missing.
Abbreviations: BMI, body mass index; MET, the metabolic equivalent of task; MHT, menopausal hormone therapy; PRS, polygenic risk score.
*
P value for t test of means or χ2 test of proportions between premenopausal and postmenopausal women; tests were performed at the two‐sided .05 significance level.