Table 2.
Association of soy consumption and risk of incident breast cancer: multivariable Cox models
| No. of cases | Person-years | Incidence rate (per 100,000 person-years)b | Adjusted hazard ratio (95% confidence intervals) | |||
|---|---|---|---|---|---|---|
| Model 1 | Model 2 | Model 3 | ||||
| Baseline soy frequency | ||||||
| Never or rarely (Median 3.2 mg/day) | 194 | 359,459 | 66.0 | 1.00 | 1.00 | 1.00 |
| Monthly (Median 4.5 mg/day) | 546 | 904,889 | 75.2 | 1.11 (0.94–1.31) | 1.10 (0.93–1.31) | 1.08 (0.91–1.28) |
| 1-3 days/week (Median 14.4 mg/day) | 1291 | 1,471,813 | 77.7 | 1.09 (0.92–1.28) | 1.07 (0.91–1.27) | 1.03 (0.87–1.22) |
| ≥ 4 days/week (Median 19.1 mg/day) | 258 | 279,390 | 78.7 | 1.05 (0.86–1.29) | 1.03 (0.84–1.26) | 0.98 (0.80–1.20) |
| P for trenda | 0.817 | 0.998 | 0.537 | |||
| Quartiles of usual soy isoflavone intake | ||||||
| Q1 (Median 4.5 mg/day) | 495 | 993,841 | 67.1 | 1.00 | 1.00 | 1.00 |
| Q2 (Median 7.2 mg/day) | 311 | 517,016 | 70.9 | 0.99 (0.84–1.17) | 0.99 (0.83–1.17) | 0.96 (0.81–1.13) |
| Q3 (Median 14.4 mg/day) | 1,309 | 1,344,269 | 80.9 | 1.11 (0.97–1.28) | 1.10 (0.96–1.26) | 1.06 (0.92–1.22) |
| Q4 (Median 19.1 mg/day) | 174 | 160,425 | 80.9 | 1.05 (0.86–1.28) | 1.03 (0.84–1.26) | 1.00 (0.81–1.22) |
| P for trenda | 0.288 | 0.379 | 0.682 | |||
Model 1: Stratified by baseline age groups and study regions and adjusted for education attainment (no formal school, primary school, middle school, or high school or above) and household income (< 10000, 10000–19999, or ≥ 20000 yuan/year)
Model 2:Adjusted for variables in model 1 plus smoking status (never or ever), alcohol consumption (weekly alcohol consumer or non-weekly consumer), physical activity (0–10.9, 11.0–17.9, 18.0–29.4, or ≥ 29.5 MET-hour/day), baseline BMI (< 24.0, 24.0–27.9, or ≥ 28.0 kg/m2 according to overweight/obesity definition of Chinese population), and standing height (continuous)
Model 3: Adjusted for variables in model 2 plus age at menarche (< 10, 11, 12, 13, 14, 15, 16, 17, 18, or ≥ 19 years old), parity (0, 1, 2, or ≥ 3), average breastfeeding duration (0, 0.1–1, 1–2, or > 2 years), menopausal status and age at menopause (pre-menopausal, menopausal age < 45 years old, menopausal age 45–49 years old, menopausal age ≥ 50 years old), use of oral contraceptives (ever or never), family history of cancer (yes or no), consumption frequency of fresh fruit, fresh vegetables, preserved vegetables, red meat, poultry, fish and dairy products at baseline (never/rarely, monthly, 1–3 days/week, 4–6 days/week, or daily), and total energy intake
aTests for trend were conducted by coding the groups as 1, 2, 3 and 4, respectively
bValues were adjusted for study region and age at study date