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Table 1 Age-adjusted characteristics of women at the time of the biopsy, stratified by menopausal status and parity

From: Associations of reproductive breast cancer risk factors with breast tissue composition

Characteristic Premenopausal, n = 601 Postmenopausal, n = 290
Nulliparous, n = 61 Parous, n = 540 Nulliparous, n = 21 Parous, n = 269
Mean (SD)
 % epithelium 8.8 (4.8) 10.4 (7.0) 4.6 (2.8) 7.2 (6.1)
 % stroma 76.1 (10.3) 74.5 (11.0) 74.0 (10.7) 67.3 (12.6)
 % fat 15.1 (11.2) 15.1 (10.9) 21.3 (9.9) 25.5 (13.5)
 % fibroglandular tissuea 84.9 (11.2) 84.9 (10.9) 78.7 (9.9) 74.5 (13.5)
Age (years)b 36.2 (7.4) 41.5 (7.3) 55.1 (7.5) 57.3 (6.5)
Age at menopause (years) NA NA 44.5 (4.9) 48.4 (5.1)
Body mass index (kg/m2) 24.2 (5.4) 24.1 (4.5) 24.5 (2.4) 25.1 (4.0)
Alcohol use (g/day) 4.2 (4.7) 5.4 (8.8) 4.3 (3.8) 5.5 (8.6)
Parity NA 2.7 (1.2) NA 3.2 (1.5)
Age at first birth (years) NA 25.1 (3.6) NA 24.9 (3.2)
Age at menarche (years) 13.0 (1.1) 12.5 (1.4) 12.9 (0.8) 12.7(1.3)
Percentagesc
 Breastfeeding
  0 to < 1 month NA 41 NA 50
  1 to < 12 months NA 32 NA 37
  12 to < 24 months NA 18 NA 10
  ≥ 24 months NA 10 NA 3
 Family history of breast cancer 10 10 22 17
 Smoking status
  Never smoked 61 56 24 49
  Past smoker 20 28 45 34
  Current smoker 20 16 31 17
 Postmenopausal hormone use
  Never used NA NA 12 29
  Past use NA NA 3 21
  Current use NA NA 74 32
  Unknown status NA NA 12 18
 Benign breast disease subtypes
  Non-proliferative 23 32 39 27
  Proliferative without atypia 70 58 45 55
  Proliferative with atypia 7 10 15 18
  1. Note: Values are means (SD) and percentages and are standardized to the age distribution of the study population
  2. Abbreviations: SD standard deviation, NA not applicable
  3. aFibroglandular tissue represents combined epithelium and stroma
  4. bValue is not age adjusted
  5. cPercentages are calculated based on non-missing values