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Table 1 Distribution of risk factors in different quartiles of total duration of breastfeeding

From: Breastfeeding in relation to risk of different breast cancer characteristics

Time in months: <4.0 ≥4.0 - <8.0 ≥8.0 - <13.0 ≥13.0 Missing
Total: 14092 n = 2908 n = 3688 n = 3484 n = 3451 n = 561
  Column percent(mean and SD in italics)
Age at baseline (years)      
    Mean (SD) 55.9 (7.7) 56.7 (7.8) 57.6 (7.7) 58.5 (8.1) 57.7 (6.7)
Education (n)      
    O-level college 74.0 72.7 69.0 65.6 80.6
    A-level college 7.7 6.7 7.4 6.2 5.0
    University 18.3 20.4 23.2 28.0 13.0
Type of occupation      
    Manual worker 40.7 39.3 37.9 40.5 45.6
    Non-manual worker 51.0 52.9 53.6 49.7 47.1
    Employer-self-employed 7.3 7.1 7.5 8.3 5.5
Married/cohabiting      
    No 32.5 30.2 27.5 28.8 35.5
    Yes 67.5 69.8 72.5 71.2 64.2
Age at menarche      
    ≤12 23.6 21.3 21.6 22.2 22.5
    >12 to <15 53.2 54.8 52.9 51.8 47.1
    ≥15 22.7 23.2 25.1 25.5 27.1
Parity      
    1 54.9 30.5 14.1 1.2 40.1
    2 35.1 55.7 59.5 41.6 36.5
    ≥3 10.0 13.9 26.4 57.2 23.4
Age at first childbirth      
    ≤20 17.0 19.7 18.8 22.3 19.4
    >20 to ≤25 38.1 41.6 42.1 43.1 34.9
    >25 to ≤30 29.7 28.2 29.4 26.5 28.3
    >30 15.1 10.4 9.7 8.1 15.9
Bilateral oophorectomy      
    No 98.7 98.4 98.6 98.7 98.8
    Yes 1.3 1.6 1.4 1.3 1.2
Age at menopause      
    Pre-/perimenopausal 39.3 36.5 31.4 30.0 26.0
    ≤45 14.5 12.2 11.6 11.3 15.0
    >45 to <53 34.7 36.4 40.0 39.9 43.1
    ≥53 10.2 13.1 15.6 17.4 12.5
Exposure to OC (ever/never)      
    No 47.3 45.7 49.3 53.5 52.8
    Yes 52.6 54.2 50.7 46.5 46.7
Exposure to HRT*      
    No 79.2 79.7 79.9 82.8 81.7
    ERT 8.0 7.5 8.4 7.8 6.0
    PRT 0.5 0.3 0.2 0.3 0.0
    CHRT 12.0 12.0 11.1 8.8 12.1
Height      
    Mean (SD) 163.5 (6.0) 163.8 (6.0) 163.6 (5.9) 163.4 (6.1) 162.8 (6.2)
Body mass index      
    Mean (SD) 25.5 (4.4) 25.3 (4.5) 25.3 (4.2) 25.7 (4.4) 26.0 (4.8)
Alcohol consumption      
    Nothing last year (teetotaler) 10.9 9.2 10.3 13.8 17.5
    Something last year (not last month) 12.1 11.4 12.0 12.2 13.7
    Something last month 76.8 79.3 77.6 73.8 67.6
Smoking      
    Never 38.2 40.6 45.4 49.9 44.4
    Current 33.2 30.6 26.5 23.0 33.9
    Ex 28.5 28.8 28.1 27.1 21.7
  1. Percentages do not always add up to 100% due to missing. *Current in peri- and postmenopausal women n = 10288.