From: Active smoking and risk of breast cancer in a Danish nurse cohort study
Birth Cohort | 1900–1934 N = 5179 | 1935–1944 N = 6707 | 1945–1949 N = 4564 | 1950–1955 N = 5381 |
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Age | ||||
Mean (SD) age at baseline (years) | 65.3 (5.8) | 53.1 (3.0) | 47.7 (1.9) | 46.4 (1.5) |
Reproductive Factors | ||||
Mean (SD) age at menarche | 14.0 (1.5) | 13.6 (1.6) | 13.4 (1.5) | 13.2 (1.5) |
Nulliparous, n (%) | 1401 (27.1) | 764 (11.4) | 431 (9.4) | 574 (10.7) |
Mean (SD) number of children in parous women | 2.5 (1.0) | 2.4 (0.9) | 2.3 (0.8) | 2.3 (0.8) |
Mean (SD) age at first birth in parous women | 27.9 (4.1) | 25.7 (3.6) | 25.0 (3.6) | 25.6 (4.2) |
Postmenopausal, n (%) | 5170 (99.8) | 5060 (75.4) | 1240 (27.2) | 906 (16.8) |
Body Mass Index (BMI) | ||||
Mean (SD) BMI (kg/m2) | 23.8 (3.5) | 23.7 (3.4) | 23.5 (3.4) | 23.8 (3.6) |
BMI < 18.5 kg/m2, n (%) | 199 (3.8) | 148 (2.2) | 100 (2.2) | 82 (1.5) |
BMI 18.5–24.9 kg/m2, n (%) | 3368 (65.0) | 4657 (69.4) | 3293 (72.2) | 3752 (69.7) |
BMI 25–29.9 kg/m2, n (%) | 1315 (25.4) | 1527 (22.8) | 944 (20.7) | 1193 (22.2) |
BMI ≥ 30 kg/m2, n (%) | 297 (5.7) | 375 (5.6) | 227 (5.0) | 354 (6.6) |
Alcohol consumption | ||||
Does not drink alcohol, n (%) | 1278 (24.7) | 980 (14.6) | 516 (11.3) | 546 (10.1) |
Moderate drinker (1–14 drinks/week), n (%) | 2900 (56.0) | 4177 (62.3) | 2923 (64.0) | 3533 (65.7) |
Heavy drinker (> 14 drinks/week), n (%) | 1001 (19.3) | 1550 (23.1) | 1125 (24.6) | 1302 (24.2) |
Leisure time physical activity | ||||
Low physical activity, n (%) | 467 (9.0) | 392 (5.8) | 250 (5.5) | 319 (5.9) |
Medium physical activity, n (%) | 1090 (21.0) | 1809 (27.0) | 1406 (30.8) | 1600 (29.7) |
High physical activity, n (%) | 3622 (69.9) | 4506 (67.2) | 2908 (63.7) | 3462 (64.3) |
Shift Work | ||||
Working night shifts, n (%) | 191 (12.5) | 453 (7.4) | 178 (4.0) | 145 (2.7) |
Hormone Use | ||||
Ever used oral contraceptives, n (%) | 2082 (40.2) | 2490 (37.1) | 779 (17.1) | 600 (11.2) |
Ever used hormone therapy, n (%) | 1143 (22.1) | 3544 (52.8) | 3462 (75.9) | 4552 (84.6) |
Smoking status | ||||
Never smoker, n (%) | 1481 (28.6) | 2487 (37.1) | 1840 (40.3) | 2115 (39.3) |
Former smoker, n (%) | 1812 (35.0) | 1716 (25.6) | 1242 (27.2) | 1787 (33.2) |
Current smoker, n (%) | 1886 (36.4) | 2504 (37.3) | 1482 (32.5) | 1479 (27.5) |
Ever smoker, n (%) | 3698 (71.4) | 4220 (62.9) | 2724 (59.7) | 3266 (60.7) |
Smoking Intensity | ||||
Mean (SD) smoking durationa (years) | 29.4 (14.5) | 23.4 (11.3) | 19.8 (9.5) | 19.4 (9.2) |
Mean (SD) smoking intensitya (g/day) | 12.1 (9.0) | 13.0 (8.8) | 12.5 (7.5) | 12.0 (7.5) |
Mean (SD) pack-yearsa | 19.5 (18.6) | 16.9 (14.9) | 13.5 (11.1) | 12.8 (11.0) |
Initiation of smoking | ||||
Mean age (SD) at smoking initiationa (years) | 22.6 (6.9) | 21.1 (5.3) | 19.6 (3.9) | 17.8 (3.3) |
Initiation of smoking in 18,661 parous women | ||||
Parous never smoker, n (%) | 1078 (28.5) | 2246 (37.8) | 1684 (40.8) | 1930 (40.2) |
Parous ever smoker, n (%) | 2700 (71.5) | 3697 (62.2) | 2449 (59.3) | 2877 (59.9) |
Parous/around 1st birth or later, n (%) | 430 (8.3) | 632 (9.4) | 259 (5.7) | 136 (2.5) |
Parous/before 1st childbirth, ≤ 10 pack-years, n (%) | 2047 (39.5) | 2824 (42.1) | 2037 (44.6) | 2459 (45.7) |
Parous/before 1st childbirth, > 10 pack-years, n (%) | 223 (4.3) | 241 (3.6) | 153 (3.4) | 282 (5.2) |
Initiation of smoking in 3170 nulliparous women | ||||
Nulliparous never smoker, n (%) | 403 (28.8) | 241 (31.5) | 156 (36.2) | 185 (32.2) |
Nulliparous ever smoker, n (%) | 998 (71.2) | 523 (68.5) | 275 (63.8) | 389 (67.8) |
Nulliparous, before age 21b years, n (%) | 442 (8.5) | 295 (4.4) | 187 (4.1) | 340 (6.3) |
Nulliparous, age 21 years or later, n (%) | 556 (10.7) | 228 (3.4) | 88 (1.9) | 49 (0.9) |
Initiation of smoking in 12,376 postmenopausal women | ||||
Postmenopausal never smoker, n (%) | 1477 (28.6) | 1757 (34.7) | 454 (36.6) | 300 (33.1) |
Postmenopausal ever smoker, n (%) | 3693 (71.4) | 3303 (65.3) | 786 (63.4) | 606 (66.9) |
Before menopause, n (%) | 3633 (70.3) | 3281 (64.8) | 782 (63.1) | 605 (66.8) |
After menopause, n (%) | 60 (1.2) | 22 (0.4) | 4 (0.3) | 1 (0.1) |