Table 1 Characteristics of the study sample.

From: DNA methylation-based biological age, genome-wide average DNA methylation, and conventional breast cancer risk factors

Characteristics

Monozygotic twins

Dizygotic twins

Sisters

Approximately normal variables, mean (standard deviation)

   Age (years)

55.6 (8.4)

57 (7.2)

56.6 (8.0)

   DNAm age (years)

      Hannum clock

56.3 (6.3)

58.4 (5.9)

57.2 (6.6)

      Horvath clock

54.8 (6.7)

56.5 (6.0)

55.5 (6.5)

      Levine clock

52.1 (6.9)

53.6 (7.2)

53.2 (7.7)

   Epigenetic age acceleration (years)

      Hannum clock

−0.5 (3.9)

0.7 (4.2)

−0.1 (4.4)

      Horvath clock

−0.4 (4.4)

0.6 (4.8)

−0.1 (4.9)

      Levine clock

−0.4 (4.8)

0.2 (5.9)

0.1 (5.8)

   Genome-wide average DNA methylation (percentage)

53.0 (0.3)

53.0 (0.3)

53.0 (0.3)

   Age at menarche (years)

13.0 (1.3)

12.9 (1.5)

13.0 (1.5)

   Age at menopause (years)a

47.0 (5.9)

45.8 (6.3)

45.8 (6.0)

   Age at first live birth (years)b

25.1 (5.3)

25.0 (4.7)

24.7 (4.8)

Skewed variables, median (inter-quartile range)

   Body mass index

24.7 (22.7–30.0)

26.4 (23.0–29.1)

25.7 (23.0–30.1)

   Pack-years of smokingc

9.0 (3.6–21.2)

7.0 (2.0–14.3)

5.0 (1.9–13.4)

   Number of live birthsb

3.0 (2.0–3.3)

3.0 (2.0–4.0)

3.0 (2.0–4.0)

   Years of hormonal replacement therapy used

2.0 (0.8–6.3)

4.8 (1.3–10.8)

3.4 (1.2–7.0)

   Years of oral contraceptive usee

5.0 (2.0–9.5)

5.0 (2.0–10.0)

5.0 (1.8–11.7)

   Mammographic densityf

     Dense area

26.4 (6.6–46.7)

26.5 (7.9–46.3)

25.7 (12.4–44.9)

     Non-dense area

109.0 (66.8–142.2)

94.7 (63.0–136.5)

98.0 (68.6–148.5)

     Percentage dense area

19.4 (4.2–41.8)

23.0 (7.3–39.8)

21.5 (9.9–37.7)

   Binary variables, N (%)

     Smoking

49 (37.1%)

47 (35.6%)

92 (42.8%)

     Alcohol drinking

77 (58.3%)

80 (60.6%)

130 (60.5%)

     Post-menopausal

81 (61.4%)

102 (77.3%)

145 (67.4%)

     Parous

116 (87.9%)

117 (88.6%)

198 (92.1%)

     Hormonal replacement therapy use

43 (32.6%)

58 (43.9%)

85 (39.5%)

     Oral contraceptive use

106 (80.3%)

111 (84.1%)

183 (85.1%)

     Family history

32 (24.2%)

14 (10.6%)

45 (20.9%)

  1. aFor post-menopausal women; bFor parous women; cFor ever smokers; dFor hormonal replacement therapy users; eFor oral contraceptive users; fSample sizes were 122, 123 and 190 for monozygotic twins, dizygotic twins and sisters, respectively.
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