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

 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

  < = 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

 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

 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-trend^a

0.003

 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 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

  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

  <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-trend^b

0.01

  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-trend^a

0.06

  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

  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-trend^a

0.27

  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

  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

  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

  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