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Table 3 Association between active smoking and breast cancer in 21,831 women in the Danish Nurse Cohort

From: Active smoking and risk of breast cancer in a Danish nurse cohort study

 

N

Person-years

No. of cases

Age adjusted

Fullya adjusted

HR (95% CI)

HR (95% CI)

Never smoked (ref.)

7923

126,950

379

1.00

1.00

 Former smoker

6557

102,190

338

1.11 (0.96–1.29)

1.08 (0.94–1.26)

 Current smoker

7351

113,400

445

1.32 (1.15–1.51)

1.27 (1.11–1.46)

 Ever smokers

13,908

215,589

783

1.22 (1.08–1.38)

1.18 (1.04–1.34)

Smoking duration among ever smokers

  ≤ 10 years

2925

47,335

156

1.10 (0.92–1.33)

1.10 (0.91–1.33)

 11–20 years

3175

50,151

175

1.17 (0.98–1,40)

1.15 (0.96–1.38)

 21–30 years

4456

68,818

259

1.26 (1.08–1.48)

1.24 (1.06–1.46)

  > 30 years

3295

49,285

193

1.32 (1.11–1.57)

1.21 (1.01–1.46)

p-value for trend

    

0.004

 Every increase of 10 years

   

1.08 (1.04–1.12)

1.06 (1.02–1-11)

Smoking (Tobacco) Intensity among ever smokers

  > 6 g/day

3098

49,245

161

1.10 (0.91–1.32)

1.07 (0.89–1.29)

 6–10 g/day

4317

67,410

235

1.17 (0.99–1.38)

1.14 (0.97–1.34)

 11–15 g/day

3050

46,962

175

1.25 (1.05–1.50)

1.22 (1.02–1.46)

  > 15 g/day

3443

51,973

212

1.37 (1.16–1.62)

1.31 (1.11–1.56)

p-value for trend

    

0.001

 Every increase of 10 g/day

   

1.05 (0.97–1.14)

1.04 (0.95–1.13)

Lifetime pack-years

  ≤ 10 pack-years

6082

96,640

327

1.13 (0.98–1.31)

1.12 (0.97–1.30)

 11–20 pack-years

3536

54,993

192

1.17 (0.99–1.39)

1.14 (0.96–1.36)

  > 20 pack-years

4290

63,956

264

1.39 (1.19–1.63)

1.32 (1.12–1.55)

p-value for trend

    

0.002

 Every increase of 20 pack-years

   

1.10 (1.01–1.20)

1.07 (0.98–1.18)

Initiation of smoking in 18,661 parous women

 Parous never smoker (ref.)

6938

111,811

326

1.00

1.00

 Parous, around first birth or later

1457

23,553

88

1.28 (1.01–1.62)

1.28 (1.00–1.62)

 Parous, before first childbirth, ≤ 10 pack-years

9367

146,965

493

1.15 (1.00–1.33)

1.13 (0.98–1.31)

 Parous, before first childbirth, > 10 pack-years

899

12,901

66

1.77 (1.36–2-31)

1.58 (1.20–2.10)

Initiation of smoking in 3170 nulliparous women

 Nulliparous never smoker (ref.)

985

15,138

53

1.00

1.00

 Nulliparous, before age 21b years

1264

18,737

74

1.14 (0.80–1.62)

1.10 (0.76–1.58)

 Nulliparous, age 21 years or later

921

13,434

62

1.31 (0.91–1.90)

1.29 (0.89–1.88)

Initiation of smoking in 12,376 postmenopausal women

 Postmenopausal never smoker (ref.)

3988

66,617

202

1.00

1.00

 Before menopause

8301

130,987

488

1.23 (1.05–1.45)

1.20 (1.01–1.41)

 After menopause

87

1252

6

1.60 (0.71–3.59)

1.66 (0.74–3.75)

Pack-years in 8347 parous postmenopausal womenc

 Parous postmenopausal never smoker (ref.)

2712

 

129

1.00

1.00

 Pack-years before 1st childbirthd

   ≤ 10 pack-years

4349

70,627

227

1.16 (0.93–1.44)

1.14 (0.92–1.42)

  11–20 pack-years

366

5233

34

2.36 (1.62–3.45)

2.16 (1.45–3.20)

   > 20 pack-years

61

854

4

1.69 (0.63–4.59)

1.38 (0.50–3.78)

   p-value for trend

    

0.006

 Pack-years from 1st childbirth until menopaused

   ≤ 10 pack-years

2572

42,484

128

1.08 (0.85–1.38)

1.03 (0.81–1.33)

  11–20 pack-years

1606

25,391

79

1.12 (0.85–1.49)

1.13 (0.85–1.50)

   > 20 pack-years

817

12,471

60

1.74 (1.28–2.36)

1.84 (1.34–2.53)

   p-value for trend

    

0.029

 Pack-years after menopaused

   ≤ 10 pack-years

2294

37,270

124

1.20 (0.94–1.53)

1.19 (0.93–1.53)

  11–20 pack-years

453

6695

20

1.09 (0.68–1.74)

1.03 (0.64–1.66)

   > 20 pack-years

1966

32,094

118

1.32 (1.03–1.70)

1.29 (0.70–4.98)

   p-value for trend

    

0.412

  1. HR hazard ratio, CI confidence interval aAdjusted for age, no of births, Body Mass Index, physical activity, alcohol use, oral contraceptive use, age at menarche, menopause, age at 1st birth, parity, number of birth, hormone therapy use, and night shift work. b21 is mean age at 1st childbirth in this cohort; c with information on age at cessation of menstrual bleeding; d every increase of 20 pack-years