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