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Table 2 Description of the Danish Nurse Cohort (n = 21,831) at the time of recruitment in 1993 or 1993 and by birth cohort

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

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)

  1. SD standard deviation; ain ever smokers. b21 is mean age of smoking initiation in the cohort