Table 2. Cox proportional hazards regression analyses for the crude HR and multiple variable-adjusted HR for risk of breast cancer in women recruited before and after menopause.
| Factors |
Pre-menopause |
Post-menopause |
||||
|---|---|---|---|---|---|---|
| Crude HR |
aHR |
Crude HR |
aHR |
|||
| (95% CI) | (95% CI) | P-value | (95% CI) | (95% CI) | P-value | |
| BMI (vs 18.5–23.9) | ||||||
| <18.5 | 0.94(0.82,1.07) | 0.94(0.81,1.10) | 0.9999a | 0.79(0.65,0.97) | 0.78(0.63,0.96) | <0.0001a |
| 24–26.9 | 0.95(0.90,1.01) | 0.98(0.91,1.04) | 1.13(1.06,1.20) | 1.19(1.12,1.27) | ||
| 27–29.9 | 0.96(0.87,1.04) | 1.02(0.93,1.13) | 1.22(1.13,1.31) | 1.31(1.21,1.41) | ||
| 30–34.9 | 0.93(0.81,1.06) | 1.01(0.86,1.18) | 1.41(1.27,1.56) | 1.53(1.38,1.71) | ||
| ⩾35 | 0.71(0.49,1.03) | 0.82(0.54,1.24)b | 1.50(1.17,1.92) | 1.65(1.27,2.13) | ||
| Age at recruitment (vs <40) | ||||||
| 40–49 | 1.26(1.19,1.34) | 1.39(1.30,1.48) | <0.0001a | 1.11(0.61,2.03) | 0.96(0.49,1.88) | <0.0001a |
| 50–59 | 1.39(1.29,1.49) | 1.72(1.56,1.90) | 1.34(0.74,2.42) | 1.25(0.65,2.41) | ||
| 60–69 | — | 1.07(0.59,1.93) | 1.21(0.63,2.33) | |||
| ⩾70 | — | 0.59(0.33,1.08) | 0.73(0.37,1.41) | |||
| Age at menarche (vs ⩽13) | ||||||
| 14 | 0.91(0.85,0.97) | 0.96(0.90,1.03) | <0.0001a | 0.88(0.82,0.95) | 0.94(0.87,1.02) | <0.0001a |
| 15 | 0.83(0.83,0.89) | 0.89(0.82,0.96) | 0.83(0.77,0.90) | 0.92(0.85,1.00) | ||
| ⩾16 | 0.76(0.76,0.82) | 0.82(0.76,0.89) | 0.66(0.62,0.71) | 0.78(0.72,0.84) | ||
| Birth (vs no) | ||||||
| Yes | 0.73(0.66,0.81) | 0.81(0.62,1.06) | 0.1186 | 0.62(0.56,0.69) | 0.67(0.54,0.83) | 0.0003 |
| No. of birthc (vs 1) | ||||||
| 2 | 0.86(0.79,0.94) | 0.91(0.82,1.00) | <0.0001a | 0.89(0.79,1.01) | 0.96(0.83,1.10) | <0.0001a |
| ⩾3 | 0.66(0.60,0.71) | 0.76(0.69,0.85) | 0.59(0.53,0.66) | 0.80(0.70,0.92) | ||
| Age at first full-term pregnancyc (vs ⩽22) | ||||||
| 23–25 | 1.29(1.20,1.39) | 1.28(1.18,1.39) | <0.0001a | 1.20(1.13,1.27) | 1.15(1.08,1.23) | <0.0001a |
| 26–29 | 1.54(1.43,1.66) | 1.46(1.35,1.58) | 1.57(1.47,1.68) | 1.33(1.23,1.44) | ||
| ⩾30 | 1.89(1.74,2.06) | 1.69(1.54,1.87) | 1.87(1.72,2.05) | 1.51(1.36,1.68) | ||
| Breast feedingc (vs no) | ||||||
| Yes | 0.86(0.82,0.91) | 0.94(0.89,0.99) | 0.0243 | 0.67(0.63,0.71) | 0.86(0.80,0.92) | <0.0001 |
| Family history (vs no) | ||||||
| Yes | 1.57(1.41,1.76) | 1.39(1.22,1.59) | <0.0001 | 2.02(1.81,2.24) | 1.68(1.48,1.90) | <0.0001 |
| Hormone therapy (vs no) | ||||||
| Yes | 1.25(0.97,1.61) | — | 1.25(1.13,1.38) | — | ||
Abbreviations: BMI, body mass index; CI, confidence interval; HR, hazards ratio. aHR: adjusted hazard ratio calculated by multiple variable Cox proportional hazards regression model for the risk of breast cancer after adjustment for all the variables include BMI, age, age at menarche, birth history, number of birth, age at the first full-term pregnancy, breast-feeding history and family history of breast cancer.
a
P-value for trend.
b
P-value=0.3575 for testing BMI ⩾35 vs BMI<35 (HR=0.82, 95% CI=0.54–1.25).
c
Among parous women.