Table 1 Characteristics of the study population
All women ( N =20 967) | BC cases ( N =815) | |
|---|---|---|
Characteristic | N (%) | N (%) |
Age, mean (s.d.) | 55 (9) | 56 (8) |
Country of birth | ||
Australia/New Zealand/Other | 15 143 (72) | 647 (79) |
The United Kingdom | 1391 (7) | 40 (5) |
Italy | 2476 (12) | 77 (9) |
Greece | 1957 (9) | 51 (6) |
Age at menarche (years) | ||
<12 | 3411 (16) | 136 (17) |
12 | 4113 (20) | 149 (18) |
13 | 5547 (26) | 216 (27) |
⩾14 | 7896 (38) | 314 (39) |
Parity | ||
Nulliparous | 3085 (15) | 147 (18) |
Parous | 17 882 (85) | 668 (82) |
Duration of lactation (months) | ||
Never | 6177 (29) | 274 (34) |
Up to 6 | 4581 (22) | 148 (18) |
7–12 | 3321 (16) | 114 (14) |
13–24 | 4044 (19) | 179 (22) |
>24 | 2844 (14) | 100 (12) |
Oral contraceptive | ||
Never user | 8378 (40) | 329 (40) |
Past user | 12 187 (58) | 472 (58) |
Current user | 402 (2) | 14 (2) |
HRT | ||
Never user | 15 566 (74) | 564 (69) |
Past user | 1774 (8) | 67 (8) |
Current user | 3627 (17) | 184 (23) |
Menopausal status | ||
Having periods | 7566 (36) | 285 (35) |
Periods stopped for natural reasons | 8970 (43) | 381 (47) |
Periods stopped for other reasonsa | 4431 (21) | 149 (18) |
Level of physical activity | ||
None | 4503 (21) | 139 (17) |
Low | 4461 (21) | 185 (23) |
Medium | 7599 (36) | 317 (39) |
High | 4404 (21) | 174 (21) |
Alcohol consumption | ||
Lifetime abstainers | 7866 (38) | 298 (37) |
Ex-drinkers | 647 (3) | 29 (4) |
1–19 g per day | 10 062 (48) | 397 (49) |
20–39 g per day | 1850 (9) | 66 (8) |
40 g per day or more | 542 (3) | 25 (3) |
Smoking | ||
Never | 14 547 (69) | 574 (70) |
Current | 1831 (9) | 63 (8) |
Former | 4589 (22) | 178 (22) |
Level of education | ||
⩽Primary school | 3902 (19) | 114 (14) |
Some high/technical school | 9029 (43) | 362 (44) |
Completed high/technical school | 3761 (18) | 153 (19) |
Degree/diploma | 4275 (20) | 186 (23) |
BMI (kg m–2), mean (s.d.) | 26.6 (4.8) | 26.9 (4.9) |
Energy from diet (Mj per day), mean (s.d.) | 8.5 (2.8) | 8.5 (2.8) |
