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Table 2 Odds ratios (ORs) and 95 % confidence intervals (95 % CIs) for breast cancer risk unadjusted and adjusted for mammographic density (MD) measures and percent of the association with breast cancer mediated by MD measures in women premenopausal at mammogram in the NHS/NHSII (N = 559 cases/1727 controls)

From: Mammographic density and breast cancer risk: a mediation analysis

Selected risk factor

OR (95 % CI)

not adjusted for MD

OR (95 % CI)

adjusted for MD

Percent mediated by MD

(p value)

Childhood somatotypea

Per 1-unit increase

 Percent MDc

0.93 (0.86,1.01)

0.98 (0.90,1.07)

71 % (p = 0.12)

 Dense areac

0.93 (0.86,1.01)

0.95 (0.88,1.04)

30 % (p = 0.14)

 Non-dense areac

0.93 (0.86,1.01)

0.96 (0.88,1.04)

35 % (p = 0.16)

Adolescent somatotypea

Per 1-unit increase

 Percent MDc

0.90 (0.82,0.99)

0.97 (0.88,1.07)

73 % (p = 0.05)

 Dense areac

0.90 (0.82,0.99)

0.92 (0.84,1.01)

22 % (p = 0.09)

 Non-dense areac

0.90 (0.82,0.99)

0.94 (0.85,1.03)

35 % (p = 0.11)

BMI at age 18 (kg/m2)a

Per 5-unit increase

Percent MDc

0.80 (0.65,0.97)

0.96 (0.78,1.19)

82 % (p = 0.04)

 Dense areac

0.80 (0.65,0.97)

0.83 (0.68,1.02)

18 % (p = 0.10)

 Non-dense areac

0.80 (0.65,0.97)

0.87 (0.70,1.08)

40 % (p = 0.11)

Weight change since 18b

Per 20-lb increase

 Percent MDc

1.03 (0.96,1.12)

1.16 (1.06,1.26)

Not mediatedd

 Dense areac

1.03 (0.96,1.12)

1.05 (0.97,1.13)

Not mediatedd

 Non-dense areac

1.03 (0.96,1.12)

1.12 (1.02,1.23)

Not mediatedd

BMI (kg/m2)

Per 5-unit increase

 Percent MDc

1.03 (0.92,1.16)

1.22 (1.07,1.39)

Not mediatedd

 Dense areac

1.03 (0.92,1.16)

1.05 (0.93,1.19)

Not mediatedd

 Non-dense areac

1.03 (0.92,1.16)

1.16 (1.01,1.33)

Not mediatedd

Height

Per 3-inch increase

 Percent MDc

1.14 (1.01,1.28)

1.14 (1.01,1.29)

Not mediatedd

 Dense areac

1.14 (1.01,1.28)

1.13 (1.00,1.27)

6 % (p = 0.43)

 Non-dense areac

1.14 (1.01,1.28)

1.15 (1.02,1.30)

Not mediatedd

Age at menarche

Per 2-year increase

 Percent MDc

0.85 (0.74,0.98)

0.83 (0.72,0.96)

Not mediatedd

 Dense areac

0.85 (0.74,0.98)

0.83 (0.72,0.96)

Not mediatedd

 Non-dense areac

0.85 (0.74,0.98)

0.84 (0.73,0.97)

Not mediatedd

Nulliparous

Nulliparous vs parous

 Percent MDc

1.15 (0.86,1.52)

1.07 (0.80,1.42)

52 % (p = 0.35)

 Dense areac

1.15 (0.86,1.52)

1.11 (0.84,1.48)

23 % (p = 0.43)

 Non-dense areac

1.15 (0.86,1.52)

1.11 (0.84,1.48)

22 % (p = 0.37)

Birth index

Per 102-unit increase

 Percent MDc

0.66 (0.43,1.01)

0.77 (0.50,1.19)

38 % (p = 0.08)

 Dense areac

0.66 (0.43,1.01)

0.69 (0.45,1.07)

13 % (p = 0.21)

 Non-dense areac

0.66 (0.43,1.01)

0.71 (0.46,1.09)

18 % (p = 0.11)

Parity (among parous)

Per one-child increase

 Percent MDc

1.00 (0.90,1.12)

1.03 (0.92,1.16)

Not mediatedd

 Dense areac

1.00 (0.90,1.12)

1.02 (0.91,1.14)

Not mediatedd

 Non-dense areac

1.00 (0.90,1.12)

1.01 (0.90,1.13)

Not mediatedd

Age at first birth (among parous)

Per 5-year increase

 Percent MDc

1.18 (1.03,1.36)

1.18 (1.02,1.36)

3 % (p = 0.58)

 Dense areac

1.18 (1.03,1.36)

1.19 (1.03,1.38)

Not mediatedd

 Non-dense areac

1.18 (1.03,1.36)

1.18 (1.02,1.36)

3 % (p = 0.28)

Breastfeeding (among parous)

Ever vs never

 Percent MDc

0.99 (0.76,1.28)

1.00 (0.77,1.30)

89 % (p = 0.92)

 Dense areac

0.99 (0.76,1.28)

0.98 (0.75,1.28)

Not mediatedd

 Non-dense areac

0.99 (0.76,1.28)

1.00 (0.77,1.30)

75 % (p = 0.92)

Breastfeeding (among parous who ever breastfed)

Per 12-month increase

 Percent MDc

0.95 (0.81,1.11)

0.93 (0.80,1.08)

Not mediatedd

 Dense areac

0.95 (0.81,1.11)

0.93 (0.79,1.08)

Not mediatedd

 Non-dense areac

0.95 (0.82,1.11)

0.95 (0.82,1.11)

1 % (p = 0.92)

Alcohol use

Per 10 g/day increase

 Percent MDc

0.98 (0.84,1.15)

0.98 (0.84,1.14)

Not mediatedd

 Dense areac

0.98 (0.84,1.15)

0.97 (0.83,1.14)

Not mediatedd

 Non-dense areac

0.98 (0.84,1.15)

0.98 (0.84,1.15)

Not mediatedd

Family history of breast cancer

Yes vs no

 Percent MDc

1.47 (1.07,2.01)

1.46 (1.06,2.00)

2 % (p = 0.76)

 Dense areac

1.47 (1.07,2.01)

1.39 (1.01,1.92)

14 % (p = 0.12)

 Non-dense areac

1.47 (1.07,2.01)

1.51 (1.10,2.07)

Not mediatedd

History of biopsy-confirmed BBD

Yes vs no

 Percent MDc

2.04 (1.59,2.62)

1.81 (1.40,2.32)

17 % (p < 0.01)

 Dense areac

2.04 (1.59,2.62)

1.80 (1.40,2.32)

18 % (p < 0.01)

 Non-dense areac

2.04 (1.59,2.62)

2.00 (1.56,2.57)

3 % (p = 0.07)

History of unconfirmed BBD

Yes vs no

 Percent MDc

1.12 (0.89,1.41)

1.03 (0.82,1.30)

73 % (p = 0.34)

 Dense areac

1.12 (0.89,1.41)

1.01 (0.81,1.28)

87 % (p = 0.33)

 Non-dense areac

1.12 (0.89,1.41)

1.11 (0.88,1.39)

9 % (p = 0.44)

  1. Adjusted for age (continuous), fasting status (no, yes), time of blood collection (12 am–5:59 am, 6:00 am–7:59 am, 8:00 am–11:59 pm), mammography batch (NHS batch 1, NHS batch 2, NHSII), current BMI (continuous), BMI at age 18 (continuous), adolescent somatotype (continuous), history of biopsy-confirmed BBD (no, yes), history of unconfirmed BBD (no, yes), nulliparity (no, yes), parity (continuous), age at first birth (continuous, nulliparous set to median), and age at menarche (continuous). Percent of the total association (on the log odds scale) between the exposure and breast cancer risk that was mediated by MD was calculated using the following equation: 1-(lnORadjusted/lnORunadjusted)
  2. BMI body mass index, BBD benign breast disease
  3. aNot adjusted for adolescent somatotype, BMI at age 18, or current BMI
  4. bNot adjusted for current BMI
  5. cSquare-root transformed
  6. dPercent mediated calculated to be <0 %
  7. Bold data in the header of column 2 in order to distinguish column 2 from column 3
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Breast Cancer Research

ISSN: 1465-542X

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