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Table 1 Characteristics of control subjects by age in Carolina Breast Cancer Study phases I and II (n = 2022)

From: Breast cancer biologic and etiologic heterogeneity by young age and menopausal status in the Carolina Breast Cancer Study: a case-control study

Risk factor <40 years, n (%) ≥40 years, n (%)
Mean age (±SD) 35.3 (±3.2) 54.8 (±9.9)
Race
 White 120 (52.0) 1080 (60.3)
 African American 104 (45.0) 684 (38.2)
 Other 7 (3.0) 27 (1.5)
BMI
 < 25 kg/m2 (normal/underweight) 97 (42.0) 652 (37.0)
 25–29.9 kg/m2 (overweight) 60 (26.0) 541 (30.7)
 ≥ 30 kg/m2 (obese) 74 (32.0) 570 (32.3)
 Missing   28
WHR
 < 0.77 92 (41.1) 523 (29.6)
 0.77–0.83 71 (31.7) 575 (32.5)
 ≥ 0.84 61 (27.2) 671 (37.9)
 Missing 7 22
Parity
 Nulliparous 50 (21.7) 180 (10.1)
 1–2 births 138 (59.7) 875 (48.9)
 ≥ 3 births 43 (18.6) 736 (41.1)
History of breastfeedinga
 Never 83 (45.9) 906 (56.4)
 Ever 98 (54.1) 700 (43.6)
Lifetime breastfeeding durationa
 Never 92 (50.8) 925 (57.7)
 > 0–3 months 27 (14.9) 225 (14.0)
 ≥ 4 months 62 (34.3) 453 (28.3)
 Missing   3
Time since last term pregnancya
 < 10 years 124 (68.5) 82 (5.1)
 10–19 years 53 (29.3) 397 (24.7)
 ≥ 20 years 4 (2.2) 1126 (70.2)
Age at first live birtha
 < 26 years 111 (61.3) 1235 (76.9)
 ≥ 26 years 70 (38.7) 371 (23.1)
Age at last live birtha
 < 30 years 109 (60.2) 976 (60.8)
 ≥ 30 years 72 (39.8) 629 (39.2)
 Missing   1
Age at menarche
 < 13 years 117 (50.9) 825 (46.2)
 ≥ 13 years 113 (49.1) 959 (53.8)
 Missing 1 7
Oral contraceptive use
 Never 34 (14.7) 694 (39.0)
 Ever 197 (85.3) 1084 (61.0)
 Missing   13
  1. BMI body mass index, WHR waist-to-hip ratio
  2. aAmong parous women