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Table 2 Associations of reproductive factors, smoking status and alcohol consumption with breast cancer risk

From: Differential patterns of reproductive and lifestyle risk factors for breast cancer according to birth cohorts among women in China, Japan and Korea

 

Overall

Birth cohorts

HR1 (95% CI)

HR2 (95% CI)

 ≤ 1920s HR2 (95% CI)

1930s HR2 (95% CI)

1940s HR2 (95% CI)

 ≥ 1950s HR2 (95% CI)

Heterogeneity Test

P-value (Q test)

I2

Menarche age

 < 13 years

1.30 (1.14–1.49)

1.41 (1.23–1.61)

1.55 (1.03–2.33)

1.54 (1.17–2.04)

1.24 (0.95–1.60)

1.30 (1.01–1.68)

0.62

0%

13–14 years

1.33 (1.20–1.46)

1.34 (1.22–1.48)

1.47 (1.17–1.84)

1.27 (1.08–1.50)

1.42 (1.16–1.75)

1.12 (0.91–1.38)

0.28

22%

15–16 years

1.19 (1.08–1.31)

1.17 (1.06–1.29)

1.07 (0.86–1.34)

1.23 (1.05–1.44)

1.18 (0.96–1.46)

1.06 (0.87–1.31)

0.63

0%

17 + years

Reference

Reference

Reference

Reference

Reference

Reference

  

(cont.)

0.95 (0.93–0.96)

0.94 (0.92–0.96)

0.91 (0.86–0.95)

0.95 (0.92–0.98)

0.95 (0.92–0.98)

0.96 (0.93–1.00)

0.29

20%

Menopause agea

 < 45 years

0.85 (0.74–0.96)

0.82 (0.72–0.94)

0.65 (0.48–0.87)

0.98 (0.81–1.19)

0.87 (0.67–1.14)

0.92 (0.44–1.91)

0.15

43%

45–49 years

0.90 (0.82–0.99)

0.84 (0.76–0.93)

0.75 (0.61–0.92)

0.91 (0.79–1.04)

0.80 (0.66–0.98)

1.24 (0.69–2.22)

0.22

32%

50–54 years

Reference

Reference

Reference

Reference

Reference

Reference

  

 ≥ 55 years

1.10 (0.90–1.35)

1.11 (0.91–1.35)

0.79 (0.52–1.19)

1.21 (0.93–1.59)

1.32 (0.80–2.18)

2.66 (0.98–7.21)

0.10

53%

Parity

Nulliparous

Reference

Reference

Reference

Reference

Reference

Reference

  

Parous

0.48 (0.43–0.53)

0.61 (0.55–0.68)

0.60 (0.49–0.73)

0.46 (0.38–0.56)

0.62 (0.51–0.77)

0.86 (0.66–1.13)

 < 0.01

78%

Age at first delivery

 ≤ 20 years

0.96 (0.85–1.09)

0.79 (0.69–0.90)

0.89 (0.69–1.14)

0.76 (0.62–0.92)

0.75 (0.57–0.97)

0.73 (0.46–1.17)

0.73

0%

21–25 years

Reference

Reference

Reference

Reference

Reference

Reference

  

26–30 years

1.25 (1.16–1.33)

1.24 (1.15–1.33)

1.29 (1.05–1.58)

1.44 (1.26–1.64)

1.28 (1.13–1.45)

1.07 (0.92–1.23)

0.02

68%

 > 30 years

1.61 (1.44–1.79)

1.52 (1.37–1.70)

1.33 (0.93–1.90)

1.62 (1.28–2.04)

1.77 (1.45–2.15)

1.31 (1.08–1.60)

0.15

43%

Nulliparous

2.35 (2.11–2.61)

1.76 (1.58–1.97)

1.74 (1.40–2.16)

2.40 (1.96–2.93)

1.77 (1.43–2.20)

1.23 (0.92–1.63)

 < 0.01

80%

Smoking

Never

Reference

Reference

Reference

Reference

Reference

Reference

  

Ever

1.17 (1.05–1.31)

1.13 (1.01–1.26)

1.25 (0.99–1.58)

1.06 (0.85–1.32)

0.86 (0.69–1.08)

1.45 (1.14–1.84)

0.01

72%

Alcohol consumption

Non-drinker

Reference

Reference

Reference

Reference

Reference

Reference

  

Current drinker

1.03 (0.95–1.12)

1.15 (1.05–1.26)

1.10 (0.90–1.33)

1.15 (0.96–1.38)

1.07 (0.91–1.26)

1.22 (1.01–1.48)

0.77

0%

  1. aThe menopause age factor was only analysed among post-menopausal women
  2. HR1: Hazard ratio adjusted for baseline age and age at first delivery
  3. HR2: Hazard ratio adjusted for baseline age, age at first delivery, and cohort
  4. A P value of the Q test < 0.1 or I2 > 50% implied a substantial difference by the stratified factors
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Breast Cancer Research

ISSN: 1465-542X

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