Table 1.
Characteristics of study participants in the African Breast Cancer Study by case-control status
| Total (N = 6,418) n (%) |
Case (n = 3,572) n (%) |
Control (n = 2,846) n (%) |
P value | |
|---|---|---|---|---|
| Study site | ||||
| Nigeria | 5359 (83.5) | 3022 (84.6) | 2337 (82.1) | 0.028 |
| Cameroon | 570 (8.9) | 298 (8.3) | 272 (9.6) | |
| Uganda | 489 (7.6) | 252 (7.1) | 237 (8.3) | |
| Age a (years) | ||||
| <35 | 1181 (18.4) | 399 (11.2) | 782 (27.5) | <0.001 |
| 35–44 | 1882 (29.3) | 1056 (29.6) | 826 (29.0) | |
| 45–54 | 1740 (27.1) | 1091 (30.6) | 649 (22.8) | |
| 55–64 | 1048 (16.3) | 642 (18.0) | 406 (14.3) | |
| ≥65 | 566 (8.8) | 383 (10.7) | 183 (6.4) | |
| Mean (SD) | 46.0 (12.7) | 48.3 (12.0) | 43.2 (12.9) | <0.001 |
| Level of education | ||||
| Elementary or less | 2441 (38.5) | 1401 (39.4) | 1040 (37.3) | <0.001 |
| Secondary | 1720 (27.1) | 963 (27.1) | 757 (27.2) | |
| Tertiary | 1581 (24.9) | 904 (25.4) | 677 (24.3) | |
| Vocational or technical | 600 (9.5) | 287 (8.1) | 313 (11.2) | |
| BMI b | ||||
| Underweight | 302 (5.0) | 173 (5.2) | 129 (4.7) | 0.356 |
| Normal weight | 2371 (38.9) | 1317 (39.4) | 1054 (38.2) | |
| Overweight | 1992 (32.7) | 1091 (32.7) | 901 (32.7) | |
| Obese | 1435 (23.5) | 760 (22.8) | 675 (24.5) | |
| Mean (SD) in kg/m2 | 26.4 (5.5) | 26.2 (5.4) | 26.5 (5.6) | 0.045 |
| Height (cm) | ||||
| <156 | 1437 (23.2) | 662 (19.4) | 775 (27.9) | <0.001 |
| 156–160 | 1673 (27.0) | 833 (24.4) | 840 (30.2) | |
| 161–165 | 1628 (26.3) | 986 (28.9) | 642 (23.1) | |
| >165 | 1458 (23.5) | 935 (27.4) | 523 (18.8) | |
| Mean (SD) | 160.7 (7.3) | 161.6 (7.5) | 159.6 (7.0) | <0.001 |
| Waist-hip ratio | ||||
| ≤0.85 | 2727 (42.5) | 1396 (39.1) | 1331 (46.8) | <0.001 |
| >0.85 | 3691 (57.5) | 2176 (60.9) | 1515 (53.2) | |
| Mean (SD) | 0.86 (0.08) | 0.86 (0.08) | 0.85 (0.08) | <0.001 |
| Alcohol consumption c | ||||
| Yes | 672 (10.9) | 447 (12.9) | 225 (8.3) | <0.001 |
| 5501 (89.1) | 3029 (87.1) | 2472 (91.7) | 15.1 (2.2) | |
| Age at menarche (years), mean (SD) | 15.1 (2.1) | 15.1 (2.0) | 0.425 | |
| Age at thelarche (years), mean (SD) | 13.2 (1.9) | 13.0 (1.8) | 13.6 (2.0) | <0.001 |
| Age at first live birth (years), mean (SD) | 23.1 (5.0) | 23.4 (5.2) | 22.8 (4.8) | <0.001 |
| Parity | ||||
| 0 | 472 (7.6) | 229 (6.7) | 243 (8.8) | 0.002 |
| 1 | 563 (9.1) | 297 (8.6) | 266 (9.6) | |
| 2–3 | 1750 (28.2) | 1009 (29.3) | 741 (26.8) | |
| 3424 (55.2) | 1905 (55.4) | 1519 (54.9) | ||
| Average duration of breastfeeding per live birth (months) | ||||
| 0–6 | 431 (7.5) | 263 (8.2) | 168 (6.6) | <0.001 |
| 7–12 | 1826 (31.7) | 1133 (35.2) | 693 (27.3) | |
| 13–18 | 2654 (46.1) | 1427 (44.3) | 1227 (48.3) | |
| ≥18 | 846 (14.7) | 395 (12.3) | 451 (17.8) | |
| Mean (SD) | 14.4 (5.7) | 13.9 (5.5) | 15.0 (5.8) | <0.001 |
| Total duration of breastfeeding (years) | ||||
| 1374 (24.0) | 795 (24.9) | 579 (22.9) | 0.001 | 621 (24.6) |
| 3–4 | 1475 (25.8) | 854 (26.7) | ||
| 5–6 | 1193 (20.9) | 678 (21.2) | 515 (20.4) | |
| 1680 (29.4) | 867 (27.1) | 813 (32.2) | ||
| Use of hormonal contraceptives d | ||||
| Yes | 1816 (29.5) | 926 (26.9) | 890 (32.7) | <0.001 |
| No | 4349 (70.5) | 2520 (73.1) | 1829 (67.3) | |
| Menopausal status | ||||
| Premenopausal | 3925 (61.2) | 1935 (54.2) | 1990 (70.0) | <0.001 |
| Postmenopausal | 2486 (38.8) | 1633 (45.8) | 853 (30.0) | |
| Family history of breast cancer | ||||
| Yes | 319 (5.2) | 201 (5.9) | 118 (4.4) | 0.006 |
| No | 5771 (94.8) | 3187 (94.1) | 2584 (95.6) | |
Abbreviations: SD, standard deviation; IQR, interquartile range; BMI, body mass index.
a
The age at the time of diagnosis for cases, and at the time of interview for controls.
b
Underweight BMI: <18.5 kg/m2; normal weight BMI: 18.5-<25 kg/m2; overweight BMI: 25.0-<30.0 kg/m2; and obese BMI: ≥30 kg/m2.
c
At least one alcoholic beverage a week for one year or longer.
d
Hormonal contraceptives include oral, injectable, implant, and intrauterine contraceptive devices.