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Table 2 Baseline distribution of study design and lifestyle risk factors by quartile of DNA methylationa

From: White blood cell DNA methylation and risk of breast cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO)

 

Q4 (high)

Q3

Q2

Q1 (low)

 
 

N

%

N

%

N

%

N

%

p value

Age at entry (years)

 <59

85

39.5

67

31.5

76

37.3

73

34.0

 

 60–64

66

30.7

79

37.1

60

29.4

76

35.4

 

 65–69

46

21.4

48

22.5

52

25.5

49

22.9

 

  > =70

18

8.4

19

8.9

16

7.8

17

7.9

 
         

0.75

Time at entry

  < =September 30,1997

134

62.3

125

58.7

114

55.9

132

61.4

 

  > =October 1, 1997

81

37.7

88

41.3

90

44.1

83

38.6

 
         

0.53

Date of DNA extraction

 Pre-extracted DNA

69

32.1

69

32.4

70

34.3

90

41.9

 

 Newly-extracted DNA

146

67.9

144

67.6

134

65.7

125

58.1

 
         

0.12

Race/ethnicity

 White, non-Hispanic

194

90.2

197

92.5

190

93.1

194

90.2

 

 Other

21

9.8

16

7.5

14

6.9

21

9.8

 
         

0.60

Body mass index (kg/m2)

 Underweight-normal (15–24.9)

77

35.8

84

39.4

98

48.3

92

43.0

 

 Overweight (25.0 − 29.9)

91

42.3

72

33.8

60

29.6

70

32.7

 

 Obese (> = 30)

47

21.9

57

26.8

45

22.2

52

24.3

 
         

0.09

Age at menarche (years)

 <12

37

17.3

44

20.7

31

15.2

46

21.4

 

 13

116

54.2

122

57.3

107

52.5

112

52.1

 

  > =14

61

28.5

47

22.1

66

32.5

57

26.5

 
         

0.26

Number of live births

 None

18

8.4

20

9.4

16

7.8

25

11.6

 

 1–2

66

30.7

65

30.5

66

32.4

73

34.0

 

  > =3

131

60.9

128

60.1

122

59.8

117

54.4

 
         

0.75

Age at first birth (years)

 <20

36

16.8

32

15.0

24

11.8

35

16.3

 

 20–24

101

47.2

94

44.1

100

49.3

95

44.2

 

 25–29

47

22.0

54

25.4

48

23.7

39

18.1

 

  > =30

12

5.6

13

6.1

15

7.4

21

9.8

 

 Nulliparous

18

8.4

20

9.4

16

7.9

25

11.6

 
         

0.56

Type of menopause

 Natural

129

60.0

136

63.9

126

61.8

145

67.4

 

 Bilateral oophorectomy

20

9.3

21

9.9

17

8.3

20

9.3

 

 Other

66

30.7

56

26.3

61

29.9

50

23.3

 
         

0.67

Age at natural menopause (years)

 <50

53

41.1

46

33.8

41

32.8

46

31.7

 

 50–54

56

43.4

69

50.7

66

52.8

72

49.7

 

 55+

20

15.5

21

15.4

18

14.4

27

18.6

 
         

0.65

History of benign breast disease

 No

133

62.7

143

69.4

130

64.4

140

66.7

 

 Yes

79

37.3

63

30.6

72

35.6

70

33.3

 
         

0.51

Smoking status

 Never

115

53.4

118

55.4

115

56.4

138

64.2

 

 Former

81

37.7

78

36.6

72

35.3

67

31.2

 

 Current

19

8.8

17

8.0

17

8.3

10

4.7

 
         

0.31

Recent alcohol intake

 No

45

22.6

54

28.0

56

29.6

56

28.0

 

 Yes

154

77.4

139

72.0

133

70.4

144

72.0

 

Family history of breast cancer

 No

169

81.3

180

86.1

168

83.2

176

83.0

 

 Yes

39

18.8

29

13.9

34

16.8

36

17.0

 
         

0.60

Hormone use

 Never

61

28.6

51

23.9

55

27.1

46

21.6

 

 Former

32

15.0

33

15.5

24

11.8

36

16.9

 

 Current

120

56.3

129

60.6

124

61.1

131

61.5

 
         

0.54

  1. aMissing values for cases and controls, respectively, were as follows: body mass index (1, 1), age at menarche (1, 0), number of livebirths (0, 2), age at first birth (0, 3), personal history of benign breast disease (11, 6), alcohol intake (35,31), family history of breast cancer (8, 8), and hormone use (2, 3). Q quartile