Table 1 Distribution of risk factors in different quartiles of total duration of breastfeeding
From: Breastfeeding in relation to risk of different breast cancer characteristics
Time in months: | <4.0 | ≥4.0 - <8.0 | ≥8.0 - <13.0 | ≥13.0 | Missing |
|---|---|---|---|---|---|
Total: 14092 | n = 2908 | n = 3688 | n = 3484 | n = 3451 | n = 561 |
Column percent(mean and SD in italics) | |||||
Age at baseline (years) | |||||
Mean (SD) | 55.9 (7.7) | 56.7 (7.8) | 57.6 (7.7) | 58.5 (8.1) | 57.7 (6.7) |
Education (n) | |||||
O-level college | 74.0 | 72.7 | 69.0 | 65.6 | 80.6 |
A-level college | 7.7 | 6.7 | 7.4 | 6.2 | 5.0 |
University | 18.3 | 20.4 | 23.2 | 28.0 | 13.0 |
Type of occupation | |||||
Manual worker | 40.7 | 39.3 | 37.9 | 40.5 | 45.6 |
Non-manual worker | 51.0 | 52.9 | 53.6 | 49.7 | 47.1 |
Employer-self-employed | 7.3 | 7.1 | 7.5 | 8.3 | 5.5 |
Married/cohabiting | |||||
No | 32.5 | 30.2 | 27.5 | 28.8 | 35.5 |
Yes | 67.5 | 69.8 | 72.5 | 71.2 | 64.2 |
Age at menarche | |||||
≤12 | 23.6 | 21.3 | 21.6 | 22.2 | 22.5 |
>12 to <15 | 53.2 | 54.8 | 52.9 | 51.8 | 47.1 |
≥15 | 22.7 | 23.2 | 25.1 | 25.5 | 27.1 |
Parity | |||||
1 | 54.9 | 30.5 | 14.1 | 1.2 | 40.1 |
2 | 35.1 | 55.7 | 59.5 | 41.6 | 36.5 |
≥3 | 10.0 | 13.9 | 26.4 | 57.2 | 23.4 |
Age at first childbirth | |||||
≤20 | 17.0 | 19.7 | 18.8 | 22.3 | 19.4 |
>20 to ≤25 | 38.1 | 41.6 | 42.1 | 43.1 | 34.9 |
>25 to ≤30 | 29.7 | 28.2 | 29.4 | 26.5 | 28.3 |
>30 | 15.1 | 10.4 | 9.7 | 8.1 | 15.9 |
Bilateral oophorectomy | |||||
No | 98.7 | 98.4 | 98.6 | 98.7 | 98.8 |
Yes | 1.3 | 1.6 | 1.4 | 1.3 | 1.2 |
Age at menopause | |||||
Pre-/perimenopausal | 39.3 | 36.5 | 31.4 | 30.0 | 26.0 |
≤45 | 14.5 | 12.2 | 11.6 | 11.3 | 15.0 |
>45 to <53 | 34.7 | 36.4 | 40.0 | 39.9 | 43.1 |
≥53 | 10.2 | 13.1 | 15.6 | 17.4 | 12.5 |
Exposure to OC (ever/never) | |||||
No | 47.3 | 45.7 | 49.3 | 53.5 | 52.8 |
Yes | 52.6 | 54.2 | 50.7 | 46.5 | 46.7 |
Exposure to HRT* | |||||
No | 79.2 | 79.7 | 79.9 | 82.8 | 81.7 |
ERT | 8.0 | 7.5 | 8.4 | 7.8 | 6.0 |
PRT | 0.5 | 0.3 | 0.2 | 0.3 | 0.0 |
CHRT | 12.0 | 12.0 | 11.1 | 8.8 | 12.1 |
Height | |||||
Mean (SD) | 163.5 (6.0) | 163.8 (6.0) | 163.6 (5.9) | 163.4 (6.1) | 162.8 (6.2) |
Body mass index | |||||
Mean (SD) | 25.5 (4.4) | 25.3 (4.5) | 25.3 (4.2) | 25.7 (4.4) | 26.0 (4.8) |
Alcohol consumption | |||||
Nothing last year (teetotaler) | 10.9 | 9.2 | 10.3 | 13.8 | 17.5 |
Something last year (not last month) | 12.1 | 11.4 | 12.0 | 12.2 | 13.7 |
Something last month | 76.8 | 79.3 | 77.6 | 73.8 | 67.6 |
Smoking | |||||
Never | 38.2 | 40.6 | 45.4 | 49.9 | 44.4 |
Current | 33.2 | 30.6 | 26.5 | 23.0 | 33.9 |
Ex | 28.5 | 28.8 | 28.1 | 27.1 | 21.7 |