Table 1 Main characteristics of cases and controls from the study population

Age, mean ± sd

56.4 ± 12.6

59.0 ± 13.2

<0.001

Geographical area, n (%)

Asturias

70 (4.0)

121 (6.4)

Barcelona

292 (16.8)

380 (20.1)

Cantabria

141 (8.1)

188 (9.9)

Gerona

47 (2.7)

57 (3.0)

Guipuzcoa

226 (13.0)

255 (13.5)

Huelva

105 (6.1)

79 (4.2)

Leon

227 (13.1)

202 (10.7)

Madrid

341 (19.6)

365 (19.3)

Navarra

226 (13.0)

181 (9.6)

Valencia

61 (3.5)

67 (3.5)

<0.001

Family history of breast cancer, n (%)

No

1288 (75.0)

1628 (85.7)

First-degree relative

256 (14.9)

166 (8.7)

Second-degree relative

174 (10.1)

106 (5.8)

<0.001

Educational level, n (%)

Less than primary school

268 (15.4)

327 (17.3)

Primary school

565 (32.6)

581 (30.7)

Secondary school

573 (33.0)

585 (30.9)

University

330 (19.0)

402 (21.2)

0.10

Tobacco smoking, n (%)

Never smoker

972 (56.0)

1141 (60.2)

Former smoker

450 (25.9)

397 (21.0)

Current smoker

314 (18.1)

357 (18.8)

0.002

Body Mass Index (kg/m²), n (%)

<18.5

30 (1.7)

43 (2.3)

18.5–24.9

789 (45.5)

899 (47.4)

25.0–29.9

590 (34.0)

601 (31.7)

≥30

327 (18.8)

352 (18.6)

0.31

Energy intake (kcal/day), mean ± sd

1861 ± 644

1754 ± 566

<0.001

Ethanol intake (g/day), mean ± sd

6.2 ± 11.5

5.3 ± 9.5

0.01

Red meat intake (g/day), mean ± sd

26.9 ± 20.2

25.2 ± 19.9

0.01

Fruit intake (g/day), mean ± sd

363 ± 239

365 ± 222

0.87

Vegetable intake (g/day), mean ± sd

196 ± 133

198 ± 119

0.60

Dairy intake (g/day), mean ± sd

321.1 ± 177.1

328.7 ± 176.7

0.24

Number of deliveries, mean ± sd

1.9 ± 1.5

2.0 ± 1.6

0.03

Menopausal status, n (%)

Premenopausal

702 (40.4)

628 (33.1)

Postmenopausal

1034 (59.6)

1267 (66.9)

<0.001

Age at first delivery, mean ± sd

26.5 ± 5.0

26.5 ± 4.7

0.82

Age at menarche, mean ± sd

12.8 ± 1.5

12.9 ± 1.5

0.02

Age at menopause, mean ± sd

48.8 ± 5.4

48.5 ± 5.3

0.18

Previous use of hormonal contraceptives, n (%)

789 (45.5)

868 (45.8)

0.83