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Table 3 Associations of reproductive variables with the percentage of different tissue types (log-transformed) in benign breast biopsy samples of premenopausal women (β coefficients and 95% confidence intervals)

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

Reproductive factor Number Tissue type
% epithelial % stroma % fat % fibroglandulara
Nulliparityb
 Nulliparous 61 − 0.22 (− 0.38; − 0.06) 0.06 (0.02; 0.10) − 0.32 (− 0.56; − 0.08) 0.03 (− 0.01; 0.06)
 Parous 540 Ref Ref Ref Ref
Breastfeeding, monthsc
 0 to < 1 210 Ref Ref Ref Ref
 1 to < 12 162 − 0.06 (− 0.18; 0.06) 0.04 (0.01; 0.07) − 0.11 (− 0.28; 0.06) 0.03 (− 0.00; 0.05)
 12 to < 24 92 − 0.02 (− 0.17; 0.13) 0.01 (− 0.03; 0.06) − 0.02 (− 0.24; 0.19) 0.00 (− 0.03; 0.04)
 ≥ 24 47 − 0.09 (− 0.30; 0.11) 0.04 (− 0.02; 0.09) − 0.18 (− 0.48; 0.11) 0.02 (− 0.02; 0.07)
 p-trend 511 0.53 0.33 0.39 0.57
Parityd
 1 62 Ref Ref Ref Ref
 2 190 0.27 (0.10; 0.44) − 0.02 ( − 0.07; 0.03) − 0.17 (− 0.42; 0.07) 0.02 (− 0.02; 0.06)
 3 167 0.25 (0.08; 0.43) − 0.04 (− 0.09; 0.01) − 0.03 (− 0.29; 0.22) − 0.00 (− 0.04; 0.04)
 ≥ 4 108 0.34 (0.14; 0.53) − 0.06 (− 0.11; − 0.00) 0.03 (− 0.25; 0.30) − 0.01 (− 0.05; 0.04)
 p-trend 527 0.01 0.02 0.25 0.23
Parity continuousd 527 0.07 (0.02; 0.11) − 0.02 (− 0.03; − 0.00) 0.03 (− 0.03; 0.10) − 0.01 (− 0.02; 0.00)
Age at first child’s birthe
 < 25 263 Ref Ref Ref Ref
 25–29 205 0.20 (0.10; 0.31) − 0.01 (− 0.04; 0.02) − 0.19 (− 0.34; − 0.03) 0.02 (− 0.01; 0.04)
 ≥ 30 59 0.23 (0.06; 0.40) − 0.05 (− 0.10; − 0.00) 0.01 (− 0.24; 0.26) − 0.01 (− 0.05; 0.03)
 p-trend 527 < 0.01 0.05 0.58 0.99
Age at first birth continuous (per 5 years)e 527 0.10 (0.03; 0.17) − 0.01 (− 0.03; 0.01) − 0.04 (− 0.14; 0.06) 4.5 × 10−3 (− 0.01; 0.02)
Age at menarchef
 < 12 115 − 0.10 (− 0.25; 0.06) − 0.01 (− 0.05; 0.03) 0.10 (− 0.13; 0.33) − 0.02 (− 0.05; 0.02)
 12 174 − 0.14 (− 0.28; − 0.00) − 0.03 (− 0.06; 0.01) 0.07 (− 0.14; 0.28) − 0.03 (− 0.07; − 0.00)
 13 187 − 0.01 (− 0.14; 0.13) − 0.02 (− 0.05; 0.02) − 0.02 (− 0.22; 0.18) − 0.01 (− 0.04; 0.02)
 > 13 125 Ref Ref Ref Ref
 p-trend 601 0.06 0.61 0.24 0.14
Age at menarche continuous (per 5 years)f 601 0.16 (− 0.02, 0.33) 0.01 (− 0.04, 0.05) − 0.13 (− 0.40, 0.13) 0.03 (− 0.02, 0.07)
Time between menarche and age at first birth, continuous (per 5 years)g 527 0.07 (− 8.0 × 10−3; 0.14) − 0.01 (− 0.03; 0.01) − 0.01 (− 0.11; 0.09) − 9.0 × 10−3 (− 0.02; 0.02)
Time since the last pregnancy, continuous (per 5 years)c 501 − 0.04 (− 0.12; 0.05) − 0.02 (− 0.04; 3.8 × 10−3) 0.07 (− 0.04; 0.19) − 0.02 (− 0.04; 2.1 × 10−3)
  1. aFibroglandular tissue represents combined epithelium and stroma
  2. bAdjusted for age (continuous), BMI (continuous), age at menarche (< 12, 12, 13, > 13), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)
  3. cAmong parous women only: adjusted for age (continuous), BMI (continuous), age at menarche (< 12, 12, 13, > 13), parity (1, 2, 3, and ≥4 children), age at first child’s birth (<25, 25-29, and ≥30 years), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)
  4. dAmong parous women only: adjusted for age (continuous), BMI (continuous), age at first birth (<25, 25-29, and ≥30 years), age at menarche (< 12, 12, 13, > 13), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)
  5. eAmong parous women only: adjusted for age (continuous), BMI (continuous), parity (1, 2, 3, and ≥4 children), age at menarche (< 12, 12, 13, > 13), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)
  6. fAdjusted for age (continuous), BMI (continuous), parous status (nulliparous, parous), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)
  7. gAmong parous women only: adjusted for age (continuous), BMI (continuous), parity (continuous), a family history of breast cancer (yes/no), NHS cohort (NHSI, NHSII), and alcohol use (none, > 0 to < 5, ≥5 g/day)