Table 1.
Baseline characteristics in the UK Biobank, by frequency of breast cancer (N = 261,853)
| Characteristic | All participants | Participants who developed |
|---|---|---|
| (n = 261,853) | Breast cancer (n = 9069) | |
| Means of age at recruitment | 59.64 ± 1.53 | |
| Ethnicity, n (%) | ||
| White | 236,135 (90.18) | 8253 (91.00) |
| Mixed other | 9273 (3.54) | 309 (3.41) |
| Asian or British Asian | 11,238 (4.29) | 374 (4.12) |
| Black or Black British | 1462 (0.56) | 32 (0.35) |
| Unknown | 2519 (0.96) | 67 (0.74) |
| Missing | 1226 (0.47) | 34 (0.37) |
| Physical activity level, n (%) | ||
| Quartile 1 | 50,535 (19.30) | 1834 (20.22) |
| Quartile 2 | 50,499 (19.29) | 1831 (20.19) |
| Quartile 3 | 50,472 (19.27) | 1711 (18.87) |
| Quartile 4 | 50,492 (19.28) | 1584 (17.47) |
| Unknown | 59,855 (22.86) | 2109 (23.26) |
| Townsend deprivation index, n (%) | ||
| Quartile 1 | 52,405 (20.01) | 1891 (20.85) |
| Quartile 2 | 52,214 (19.94) | 1799 (19.84) |
| Quartile 3 | 52,312 (19.98) | 1803 (19.88) |
| Quartile 4 | 52,305 (19.97) | 1889 (20.83) |
| Quartile 5 | 52,305 (19.97) | 1683 (18.56) |
| Unknown | 312 (0.12) | 4 (0.04) |
| Employment, n (%) | ||
| In paid employment | 144,683 (55.25) | 4778 (52.68) |
| Retired | 89,602 (34.22) | 3450 (38.04) |
| Not in paid employment | 26,100 (9.97) | 795 (8.77) |
| Unknown | 1468 (0.56) | 46 (0.51) |
| Qualification, n (%) | ||
| College/university degree/NVQ | 113,318 (43.28) | 3855 (42.51) |
| National examination at ages 17–18 | 36,889 (14.09) | 1282 (14.14) |
| National examination at age 16 | 93,191 (35.59) | 3257 (35.91) |
| Others/unknown | 18,455 (7.05) | 675 (7.44) |
| Body mass index(kg/m2), n (%) | ||
| < 18.5 | 1997 (0.76) | 57 (0.63) |
| 18.5 to < 25 | 101,395 (38.72) | 3251 (35.85) |
| 25 to < 30 | 95,394 (36.43) | 3396 (37.45) |
| ≥ 30 | 61,665 (23.55) | 2317 (25.55) |
| Unknown | 1402 (0.54) | 48 (0.53) |
| Alcohol intake frequency, n (%) | ||
| ≥ once/day | 41,853 (15.98) | 1634 (18.02) |
| < once/day | 219,291 (83.75) | 7418 (81.80) |
| Unknown | 709 (0.27) | 17 (0.19) |
| Smoking, n (%) | ||
| Never | 155,651 (59.44) | 5213 (57.48) |
| Previous | 81,280 (31.04) | 2966 (32.70) |
| Current | 23,476 (8.97) | 852 (9.39) |
| Unknown | 1446 (0.55) | 38 (0.42) |
| Number of births, n (%) | ||
| 0 | 48,862 (18.66) | 1787 (19.70) |
| 1 | 34,895 (13.33) | 1252 (13.81) |
| 2 | 114,079 (43.57) | 3948 (43.53) |
| ≥ 3 | 63,216 (24.14) | 2060 (22.71) |
| Unknown | 801 (0.31) | 22 (0.24) |
| Age at menarche—years, n (%) | ||
| < 13 | 98,504 (37.62) | 3562 (39.28) |
| 13–15 | 139,793 (53.39) | 4724 (52.09) |
| 16 to < 30 | 15,034 (5.74) | 526 (5.80) |
| Unknown | 8522 (3.25) | 257 (2.83) |
| Menopausal status, n (%) | ||
| No | 63,520 (24.26) | 1892 (20.86) |
| Yes | 156,335 (59.7) | 5709 (62.95) |
| Not sure—had a hysterectomy | 29,912 (11.42) | 1063 (11.72) |
| Not sure—other reason | 11,107 (4.24) | 379 (4.18) |
| Unknown | 979 (0.37) | 26 (0.29) |
| Age at frst birth—years, n (%) | ||
| < 23 | 51,487 (19.66) | 1696 (18.70) |
| 23–27 | 71,581 (27.34) | 2387 (26.32) |
| > 27 | 54,226 (20.71) | 1925 (21.23) |
| Unknown | 84,559 (32.29) | 3061 (33.75) |
| Oral contraceptive pill use, n (%) | ||
| No | 48,881 (18.67) | 1759 (19.40) |
| Yes | 211,593 (80.81) | 7275 (80.22) |
| Unknown | 1379 (0.53) | 35 (0.39) |
| Hormone replacement therapy, n (%) | ||
| No | 160,979 (61.48) | 5222 (57.58) |
| Yes | 99,350 (37.94) | 3800 (41.90) |
| Unknown | 1524 (0.58) | 47 (0.52) |
| Family history, n (%) | ||
| No | 216,149 (82.55) | 7062 (77.87) |
| Yes | 26,537 (10.13) | 1365 (15.05) |
| Unknown | 19,167 (7.32) | 642 (7.08) |
NVQ national vocational qualification