Table 1 Descriptives of study sample according to MHT use at study entry

Number of women, n (%)

102,058 (63.4)

40,778 (25.4)

5,630 (3.5)

12,415 (7.7)

Invasive breast cancer cases

4,297 (4.1)

2,599 (6.4)

262 (4.7)

686 (5.5)

Age at study entry (yrs)

53.9 ± 0.01

53.2 ± 0.03

53.4 ± 0.07

52.6 ± 0.06

Age at menarche (yrs)

13.3 ± 0.00

13.3 ± 0.01

13.2 ± 0.02

13.3 ± 0.01

Missing, n (%)

1,797 (1.8)

524 (1.3)

86 (1.5)

259 (2.1)

Age at menopause (yrs)

49.5 ± 0.02

49.7 ± 0.03

46.2 ± 0.08

48.3 ± 0.06

Missing, n (%)

47,676 (46.7)

10,731 (26.3)

1,193 (21.2)

4,075 (32.8)

Age at first birth (yrs)²

24.2 ± 0.02

23.8 ± 0.02

23.3 ± 0.06

23.4 ± 0.04

Missing, n (%)

49 (0.1)

2 (0.0)

0 (0.0)

0 (0.0)

Parity

2.3 ± 0.00

2.2 ± 0.01

2.1 ± 0.01

2.3 ± 0.01

Missing, n (%)

0 (0)

0 (0)

0 (0)

0 (0)

BMI (kg/m²)

24.7 ± 0.01

24.3 ± 0.02

24.7 ± 0.05

24.6 ± 0.04

Missing, n (%)

2,167 (2.1)

706 (1.7)

119 (2.1)

365 (2.9)

Alcohol consumption (g/day)

3.49 ± 0.02

4.23 ± 0.03

4.03 ± 0.07

3.46 ± 0.05

 Missing, n (%)

4,088 (4.0)

2,133 (5.2)

282 (5.0)

845 (6.8)

Education, n (%)

   ≤ 9 yrs

22,535 (22.1)

7,793 (19.1)

1,108 (19.7)

3,584 (28.9)

  10–12 yrs

32,513 (31.9)

13,593 (33.3)

1,946 (34.6)

3,967 (32.0)

  13–16 yrs

26,796 (26.3)

11,070 (27.2)

1,472 (26.2)

2,586 (20.8)

   ≥ 17 yrs

14,407 (14.1)

6,148 (15.1)

774 (13.8)

1,264 (10.2)

  Missing

5,807 (5.7)

2,174 (5.3)

330 (5.9)

1,014 (8.2)

Family history of breast cancer, n (%)

  None

94,481 (92.6)

37,774 (92.6)

5,198 (92.3)

11,491 (92.6)

  Mother and sister

301 (0.3)

108 (0.3)

10 (0.2)

40 (0.3)

  Mother

5,176 (5.1)

1,996 (4.9)

301 (5.4)

573 (4.6)

  Sister

2,100 (2.1)

900 (2.2)

121 (2.2)

311 (2.5)

  Missing

0 (0)

0 (0)

0 (0)

0 (0)

Smoking status, n (%)

  Never

37,843 (37.1)

12,842 (31.5)

1,870 (33.2)

3,964 (31.9)

  Former

33,783 (33.1)

15,368 (37.7)

2,118 (37.6)

4,099 (33.0)

  Current

29,502 (28.9)

12,358 (30.3)

1,602 (28.5)

4,109 (33.1)

  Missing

930 (0.9)

210 (0.5)

40 (0.7)

243 (2.0)

Physical activity, n (%)

  Low

22,411 (22.0)

9,386 (23.0)

1,382 (24.6)

3,026 (24.4)

  Moderate

54,820 (53.7)

22,735 (55.8)

3,053 (54.2)

6,001 (48.3)

  High

17,013 (16.7)

6,507 (16.0)

885 (15.7)

1,782 (14.4)

  Missing

7,814 (7.7)

2,150 (5.3)

310 (5.5)

1,606 (12.9)

Oral contraceptive use, n (%)

  Never

43,708 (42.8)

16,551 (40.6)

2,496 (44.3)

5,466 (44.0)

  Ever

54,967 (53.9)

23,584 (57.8)

3,015 (53.6)

6,406 (51.6)

  Missing

3,383 (3.3)

643 (1.6)

119 (2.1)

543 (4.4)