Table 1 Demographic and hormone-related risk factors

Number of subjects

1,366 (79.2%)

83 (4.8%)

276 (16.0%)

440

Mean age at reference date (SD), years

42.5 (5.4)

42.8 (5.2)

44.0 (4.6)

0.0001^a,b

42.6 (4.9)

Race

   White

1,206 (88.3%)

77 (92.8%)

238 (86.2%)

405 (92.0%)

   African-American

160 (11.7%)

6 (7.2%)

38 (13.8%)

0.26^c

35 (8.0%)

Education

   High school or lower

262 (19.2%)

19 (22.9%)

76 (27.5%)

60 (13.6%)

   Technical school or some college

489 (35.8%)

28 (33.7%)

103 (37.3%)

150 (34.1%)

   College graduate

615 (45.0%)

36 (43.4%)

97 (35.2%)

0.01^c,d

230 (52.3%)

First-degree breast cancer family history

   No

1,091 (79.9%)

63 (75.9%)

224 (81.1%)

388 (88.2%)

   Yes

229 (16.7%)

19 (22.9%)

46 (16.7%)

41 (9.3%)

   Unknown^e

46 (3.4%)

1 (1.2%)

6 (2.2%)

0.39^c

11 (2.5%)

Mean age at menarche (SD), years

12.4 (1.5)

12.6 (1.7)

12.4 (1.4)

0.51^a

12.7 (1.5)

Ever had a full-term (>26-week) pregnancy

66.6%

74.7%

68.5%

0.28^c

71.6%

Mean number of full-term pregnancies (SD)

2.1 (1.0)

2.1 (1.1)

2.1 (0.9)

0.92^a

2.2 (1.1)

Mean age at first full-term pregnancy (SD)

26.7 (6.4)

26.2 (6.2)

24.9 (5.8)

0.002^a,b

27.1 (6.2)

Ever breastfed among parous women

80.4%

77.4%

70.9%

0.01^c,d

87.9%

Mean duration of breastfeeding (all pregnancies) among those who breastfed (SD), months

14.2 (16.3)

13.7 (13.6)

12.6 (14.6)

0.56^a

16.6 (17.3)

Mean BMI 1 year before reference date (SD), kg/m²

25.8 (6.1)

26.2 (6.4)

26.6 (6.5)

0.12^a

25.7 (6.4)

Ever used COC

85.9%

84.3%

85.9%

0.92^c

89.3%

Mean duration of COC use among users (SD), years

6.9 (6.3)

5.8 (6.6)

6.4 (6.4)

0.23^a

6.7 (6.2)

Alcohol drinking status during reference age

   Never

428 (31.3%)

34 (41.0%)

96 (37.8%)

141 (32.1%)

   Former

259 (19.0%)

16 (19.3%)

53 (19.2%)

90 (20.5%)

   Current

679 (49.7%)

33 (39.7%)

127 (46.0%)

0.30^c

209 (47.5%)

Alcohol drinking status in recent 5-year period

   No

428 (31.3%)

34 (41.0%)

96 (34.8%)

141 (32.1%)

   Yes

759 (55.6%)

40 (48.2%)

137 (49.6%)

228 (51.8%)

   Yes, but not in the five year period

179 (13.1%)

9 (10.8%)

43 (15.6%)

0.17^c

71 (16.1%)

Mean number of alcoholic drinks per week in recent 5 years for drinkers (SD)

6.6 (20.1)

4.9 (6.1)

6.0 (8.4)

0.80^a

4.6 (9.1)