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Table 1 Adjusted odds ratios (ORs) and 95% confidence intervals (CI) for association between breast cancer overall and education and reproductive and hormonal risk factors

From: Parity, hormones and breast cancer subtypes - results from a large nested case-control study in a national screening program

Characteristics Overall
Total (n) Controls (n) Cases (n) OR* 95% CI
Education
 No education/primary school 8584 7192 1392 1 Ref
 High school 12,781 10,582 2199 1.07 (0.99, 1.15)
 University Bachelor’s degree 6179 5081 1098 1.11 (1.01, 1.22)
 University Master’s degree 3740 3077 663 1.10 (0.98, 1.22)
p-trend*     0.03  
BMI (kg/m2)
  < = 22 5141 4333 808 1 Reference
 23–25 9655 8075 1580 1.07 (0.98, 1.18)
 26–28 8131 6694 1437 1.19 (1.08, 1.32)
 >28 8357 6830 1527 1.23 (1.12, 1.36)
p-trend     <0.0001  
Age at menarche (years)
 9–12 9296 7615 1681 1 Reference
 13 8628 7157 1471 0.93 (0.86, 1.01)
 14 7704 6439 1265 0.89 (0.82, 0.97)
 15–18 5656 4721 935 0.90 (0.82, 0.98)
p-trend     0.01  
Age at first birth (years)
 13–20 8413 7085 1328 1 Reference
 21–22 4994 4170 824 1.04 (0.94, 1.15)
 23–25 6673 5580 1093 1.02 (0.93, 1.12)
 26–30 5440 4497 943 1.09 (0.98, 1.20)
 31–50 2070 1641 429 1.29 (1.12, 1.48)
 Never given birth (nulliparous) 2730 2144 586 1.73 (1.49, 2.01)
p-trenda     0.003  
Number of pregnancies lasting 6+ months
 0 2730 2144 586 1 Reference
 1 3584 2911 673 0.83 (0.73, 0.94)
 2 13499 11000 2301 0.76 (0.68, 0.84)
 3 8307 6956 1351 0.71 (0.63, 0.79)
 >4 3164 2723 441 0.59 (0.51, 0.68)
p-trend     <0.0001  
Parous women only
 Duration of breastfeeding (months)
  Parous no breastfeeding 2201 1840 361 1 Reference
   1–6 6872 5775 1097 0.97 (0.84, 1.11)
   7–12 6662 5452 1210 1.16 (1.01, 1.34)
   13–20 5466 4544 922 1.08 (0.93, 1.25)
   21–30 3620 3043 577 1.04 (0.88, 1.22)
   >30 2067 1736 331 1.10 (0.91, 1.33)
    p-trend     0.14  
 Menopausal status
  Premenopausal 2568 2035 533 1 Reference
  Perimenopausal 2279 1876 403 0.73 (0.63, 0.86)
  Postmenopausal 26437 22000 4416 0.66 (0.59, 0.75)
   p-trend     <0.0001  
 Age at menopause (years)
  <47 5412 4595 817 1 Reference
  47–49 5151 4324 827 1.10 (0.99, 1.22)
  50–52 9831 8218 1613 1.13 (1.03, 1.24)
  >52 6663 5508 1155 1.15 (1.04, 1.28)
  Premenopausal 2568 2035 533 1.81 (1.57, 2.10)
   p-trendb     0.01  
 Age at start of oral contraceptives (years)
  14–18 3097 2577 520 1 Reference
  19–20 3356 2686 670 1.19 (1.02, 1.38)
  21–24 4190 3490 700 0.95 (0.82, 1.11)
  25–50 4307 3590 717 0.91 (0.77, 1.07)
  Never used 14532 12000 2443 0.95 (0.85, 1.07)
   p-trenda     0.06  
 Duration of oral contraceptives (years)
  Never used 14532 12000 2443 1 Reference
  <2 4019 3405 614 0.89 (0.81, 0.99)
  2–5 3758 3120 638 1.02 (0.92, 1.13)
  6–10 3453 2834 619 1.10 (0.99, 1.22)
  >10 2718 2203 515 1.11 (1.00, 1.25)
   p-trend     0.01  
 Age at start of intrauterine device (years)
  14–28 1340 1120 220 1 Reference
  29–35 1422 1174 248 1.03 (0.84, 1.27)
  36–42 1193 965 228 1.18 (0.95, 1.46)
  43–50 1052 859 193 1.06 (0.85, 1.33)
  Never used 21734 18000 3693 0.99 (0.84, 1.16)
   p-trenda     0.27  
 Duration of intrauterine device (years)
  Never used 21734 18000 3693 1 Reference
  <2 729 612 117 0.92 (0.75, 1.14)
  2–5 969 791 178 1.07 (0.90, 1.28)
  6–10 1403 1158 245 1.10 (0.95, 1.28)
  >10 1753 1432 321 1.14 (0.99, 1.30)
   p-trend     0.03  
 Hormone therapy use
  Never 15688 13000 2487 1 Reference
  Past 10548 8656 1892 1.16 (1.08, 1.25)
  Estrogen current 1468 1219 249 1.03 (0.88, 1.20)
  Estrogen and progesterone current 953 661 292 2.32 (1.97, 2.72)
   p-trend     <0.0001  
 Duration of hormone therapy (years)
  Never used 15688 13000 2487 1 Reference
   < =3 3636 3066 570 1.00 (0.90, 1.10)
  4–8 2449 2013 436 1.17 (1.03, 1.30)
  >8 4060 3151 909 1.58 (1.42, 1.70)
   p-trend     <0.0001  
 Duration of estrogen and progesterone therapy (years)
  Never used 15688 13000 2487 1 Reference
   < =5 4288 3552 736 1.13 (1.02, 1.25)
  >5 4189 3238 951 1.61 (1.46, 1.78)
   p-trend     <0.0001  
  1. aThe category Never used was not included in the analysis of p-trend. bThe category Premenopausal was not included in the analysis of p-trend. *p for trend and OR mutually adjusted for age (50–54, 55–59, 60–64, 65–70 years at screening), body mass index (BMI) (≤22, 23–25, 26–28, >28 at screening), education (no education/primary school, high school, bachelor’s or master’s degree), age at menarche (9–12, 13, 14, 15–18 years), number of pregnancies (0, 1, 2, 3, ≥4), menopausal status (premenopausal, perimenopausal, postmenopausal)