Table 1.
Distributions of participants’ characteristics and their corresponding hazard ratio for breast cancer among women, the Singapore Chinese Health Study
| Characteristics | Non-cancer cases, N (%) | Breast cancer cases, N (%) | HR1 (95% CI) | P 1 |
|---|---|---|---|---|
| Body mass index§, kg/m2 | ||||
| < 18.5 | 992 (7.2) | 24 (5.4) | 1.00 (ref) | 0.002 |
| 18.5 to < 23.0 | 5700 (41.1) | 159 (36.0) | 1.09 (0.71, 1.68) | |
| 23.0 to < 27.5 | 5521 (39.8) | 195 (44.1) | 1.43 (0.93, 2.18) | |
| ≥ 27.5 | 1650 (11.9) | 64 (14.5) | 1.56 (0.97, 2.49) | |
| Level of education | ||||
| No formal education | 4471 (32.3) | 109 (24.7) | 1.00 (ref) | 0.013 |
| Primary school | 5840 (42.1) | 194 (43.9) | 1.24 (0.97, 1.58) | |
| Secondary school and above | 3552 (25.6) | 139 (31.5) | 1.42 (1.08, 1.86) | |
| Alcohol consumption§ (drinks/week) | ||||
| None | 12,403 (89.5) | 385 (87.1) | 1.00 (ref) | 0.15 |
| < 7 | 1283 (9.3) | 48 (10.9) | 1.14 (0.84, 1.53) | |
| ≥ 7 | 177 (1.3) | 9 (2.0) | 1.57 (0.81, 3.05) | |
| Physical activity (weekly) | ||||
| No | 10,103 (72.9) | 318 (72.0) | 1.00 (ref) | 0.91 |
| Yes | 3760 (27.1) | 124 (28.1) | 1.01 (0.82, 1.25) | |
| Smoking status§ | ||||
| Never | 12,639 (91.2) | 414 (93.7) | 1.00 (ref) | 0.39 |
| Former/current | 1224 (8.8) | 28 (6.3) | 0.84 (0.57, 1.24) | |
| Age when period became regular§ | ||||
| < 13 | 1918 (13.8) | 70 (15.8) | 1.61 (1.09, 2.38) | 0.016 |
| 13–14 | 4977 (35.9) | 175 (39.6) | 1.61 (1.14, 2.26) | |
| 15–16 | 4435 (31.9) | 143 (32.4) | 1.53 (1.08, 2.16) | |
| ≥ 17 | 2045 (14.8) | 42 (9.5) | 1.00 (ref) | |
| Never regular | 488 (3.5) | 12 (2.7) | 1.13 (0.59, 2.15) | |
| Age at first live birth | ||||
| < 20.0 | 2363 (17.1) | 57 (12.9) | 1.00 (ref) | 0.005 |
| 21.0–25.0 | 5195 (37.5) | 162 (36.7) | 1.19 (0.88, 1.61) | |
| 26.0–30.0 | 3840 (27.7) | 122 (27.6) | 1.15 (0.84, 1.59) | |
| ≥ 31 | 1475 (10.6) | 51 (11.5) | 1.27 (0.86, 1.86) | |
| Nulliparous | 990 (7.1) | 50 (11.3) | 1.90 (1.29, 2.80) | |
| Number of live births | ||||
| 0 | 977 (7.1) | 50 (11.3) | 1.00 (ref) | 0.0002 |
| 1–2 | 4213 (30.4) | 159 (36.0) | 0.70 (0.51, 0.97) | |
| 3–4 | 5591 (40.3) | 157 (35.5) | 0.54 (0.39, 0.74) | |
| ≥ 5 | 3082 (22.2) | 76 (17.2) | 0.54 (0.37, 0.79) | |
| Age at menopause§ | ||||
| ≤ 49 | 2371 (17.1) | 54 (12.2) | 1.00 (ref) | 0.05 |
| 50–54 | 3284 (23.7) | 92 (20.8) | 1.21 (0.86, 1.69) | |
| ≥ 55 | 8208 (59.2) | 296 (67.0) | 1.43 (1.00, 2.05) | |
| Family history of breast cancer | ||||
| No | 13,631 (98.3) | 434 (98.2) | 1.00 (ref) | 0.96 |
| Yes | 232 (1.7) | 8 (1.8) | 1.02 (0.51, 2.05) | |
| Use of hormone therapy§ | ||||
| Never | 11,543 (83.3) | 347 (78.5) | 1.00 (ref) | 0.10 |
| Ever | 1540 (11.1) | 62 (14.0) | 1.26 (0.96, 1.65) | |
| Current | 780 (5.6) | 33 (7.5) | 1.21 (0.84, 1.74) | |
| Use of oral contraceptive | ||||
| Never | 9586 (69.2) | 302 (68.3) | 1.00 (ref) | 0.70 |
| Former/current | 4277 (30.9) | 140 (31.7) | 0.98 (0.78, 1.18) | |
| Sleeping hours | ||||
| ≤ 6 h | 4737 (34.2) | 134 (30.3) | 0.84 (0.69, 1.04) | 0.48 |
| 7–8 h | 8218 (59.3) | 285 (64.5) | 1.00 (ref) | |
| ≥ 8 h | 908 (6.6) | 23 (5.2) | 0.75 (0.49, 1.15) | |
Values are presented as frequency (%) or mean (SD). Percentages may not add up to 100% due to rounding
CI confidence intervals, HR hazard ratio
§Updated with data from the first follow-up interview
1Hazard ratios and P values for linear trend were derived from the Cox proportional hazard regression models that also included age at blood collection and dialect (Hokkien or Cantonese)