Characteristics of study population
| Cases (n=1134) | Controls (n=1179) | Never night shift workers (n=1524) | Ever night shift workers (n=789) | |
|---|---|---|---|---|
| Mean (SD)/n (%) | Mean (SD)/n (%) | Mean (SD)/n (%) | Mean (SD)/n (%) | |
| Age | 57.30 (10.3) | 56.72 (10.0) | 58.0 (10.3) | 55.1 (9.6) |
| Body mass index | 25.68 (5.5) | 25.28 (5.8) | 25.3 (5.4) | 25.8 (6.2) |
| Ethnicity | ||||
| European | 707 (62.4) | 921 (78.3) | 1043 (68.5) | 585 (74.2) |
| Chinese | 239 (21.1) | 114 (9.7) | 262 (17.2) | 91 (11.6) |
| South Asian | 34 (3.0) | 35 (3.0) | 55 (3.6) | 14 (1.8) |
| Filipino | 60 (5.3) | 38 (3.2) | 57 (3.7) | 41 (5.2) |
| Japanese | 24 (2.1) | 14 (1.2) | 23 (1.5) | 15 (1.9) |
| Mixed | 19 (1.7) | 12 (1.0) | 17 (1.1) | 14 (1.8) |
| Other | 51 (4.5) | 43 (3.7) | 66 (4.3) | 28 (3.5) |
| Household income | ||||
| <$30 000 | 203 (17.9) | 121 (10.3) | 217 (14.2) | 107 (13.6) |
| $30 000–$59 999 | 279 (24.6) | 269 (22.8) | 355 (23.3) | 193 (24.5) |
| $60 000–$99 999 | 245 (21.6) | 288 (24.4) | 334 (21.9) | 199 (25.2) |
| >$100 000 | 238 (21.0) | 339 (28.8) | 372 (24.4) | 205 (26.0) |
| Not stated | 169 (14.9) | 162 (13.8)) | 246 (16.1) | 85 (10.9) |
| Education | ||||
| High school or less | 392 (34.8) | 300 (25.5) | 499 (33.0) | 193 (24.5) |
| College/trade certificate | 344 (30.6) | 349 (29.7) | 434 (28.7) | 259 (32.9) |
| Undergraduate degree | 264 (23.5) | 302 (25.7) | 356 (23.5) | 210 (26.7) |
| Graduate/professional degree | 126 (11.2) | 225 (19.1) | 225 (14.9) | 126 (16.0) |
| Menopausal status | ||||
| Premenopausal | 391 (34.6) | 445 (37.8) | 492 (32.4) | 344 (43.7) |
| Postmenopausal | 739 (65.4) | 732 (62.2) | 1028 (67.6) | 443 (56.3) |
| Medication use | ||||
| Fertility drugs (ever/never) | 63 (5.6) | 64 (5.4) | 86 (5.7) | 41 (5.2) |
| Number of years NSAID use | ||||
| None | 994 (87.7) | 992 (84.1) | 1328 (87.1) | 658 (83.4) |
| <2.34 | 55 (4.9) | 62 (5.3) | 69 (4.5) | 48 (6.1) |
| 2.34–8.50 | 48 (4.2) | 61 (5.2) | 72 (4.7) | 37 (5.0) |
| ≥8.51 | 37 (3.3) | 64 (5.4) | 55 (3.6) | 46 (5.8) |
| Number of years oral contraceptive use | ||||
| None | 558 (49.2) | 429 (36.4) | 695 (45.6) | 292 (37.0) |
| <4.50 | 192 (16.9) | 248 (21.0) | 277 (18.2) | 163 (20.7) |
| 4.50–10.00 | 215 (19.0) | 276 (23.4) | 317 (20.8) | 174 (22.1) |
| ≥10.01 | 169 (14.9) | 226 (19.2) | 235 (15.4) | 160 (20.3) |
| Number of years antidepressant use | ||||
| None | 911 (80.3) | 916 (77.8) | 1229 (80.7) | 598 (75.8) |
| <1.50 | 74 (6.5) | 86 (7.3) | 102 (6.7) | 58 (7.4) |
| 1.50–7.50 | 87 (7.7) | 87 (7.4) | 95 (6.2) | 79 (10.0) |
| ≥7.51 | 62 (5.5) | 89 (7.6) | 97 (6.4) | 54 (6.8) |
| Number of years HRT use | ||||
| None | 833 (73.5) | 854 (72.4) | 1112 (73.0) | 575 (72.9) |
| <5.00 | 91 (8.0) | 99 (8.4) | 120 (7.9) | 70 (8.9) |
| 5.00–12.00 | 114 (10.1) | 120 (10.2) | 156 (10.2) | 78 (9.9) |
| ≥12.01 | 96 (8.5) | 106 (9.0) | 136 (8.9) | 66 (8.4) |
| Reproductive history | ||||
| Age at menarche | 12.89 (1.6) | 12.84 (1.5) | 12.9 (1.5) | 12.7 (1.6) |
| Ever been pregnant | 937 (82.9) | 937 (79.6) | 1234 (81.2) | 640 (81.3) |
| Age at first pregnancy* | 27.69 (5.4) | 27.54 (5.3) | 27.6 (5.4) | 27.6 (5.4) |
| Breastfeeding (number of months) | 6.9 (9.8) | 7.9 (10.4) | 7.1 (10.0) | 7.9 (10.5) |
| Number of pregnancies* | 2.28 (1.7) | 2.25 (1.7) | 2.3 (1.7) | 2.3 (1.7) |
| Age at first mammogram | 44.72 (8.8) | 42.78 (7.5) | 44.4 (8.5) | 42 (7.6) |
| Family history of breast cancer | 223 (19.7) | 168 (14.3) | 267 (17.5) | 124 (15.7) |
| Lifestyle characteristics | ||||
| Current smoker | 72 (6.4) | 71 (6.0) | 89 (5.9) | 54 (6.9) |
| Pack-years smoking | 5.64 (12.1) | 5.29 (11.2) | 5.3 (11.8) | 5.7 (11.5) |
| Lifetime alcohol consumption (number of drinks/week) | ||||
| Teen | 1.05 (3.5) | 1.63 (4.0) | 1.1 (3.1) | 1.9 (4.7) |
| 20s | 2.24 (3.9) | 3.26 (6.1) | 2.5 (5.2) | 3.3 (5.0) |
| 30s | 2.91 (6.0) | 3.61 (5.8) | 3.0 (5.6) | 3.7 (6.4) |
| 40s | 3.10 (6.0) | 3.75 (6.1) | 3.3 (6.2) | 3.6 (5.7) |
| 50s | 2.76 (4.9) | 3.71 (6.1) | 3.2 (5.6) | 3.3 (5.3) |
*Among parous women only.