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Table 3 Adjusted mean percentage mammographic density according to smoking exposure among current smokers, and according to time since smoking cessation among former smokers

From: Different measures of smoking exposure and mammographic density in postmenopausal Norwegian women: a cross-sectional study

Smoking exposure

n

Adjusted mean percent mammographic density (95% confidence interval)

  

Current smokers

Former smokers

Number of cigarettes smoked per day

   ≤ 7 cigarettes

87

10.3 (8.2–12.8)

 

   8–10 cigarettes

79

9.0 (7.0–11.5)

 

   ≥ 11 cigarettes

77

6.6 (5.2–84)

 

P trend

 

0.008

 

Number of years smoked

   ≤ 25 years

56

8.9 (6.8–11.8)

 

   26–40 years

92

8.8 (6.9–11.3)

 

   ≥ 41 years

95

8.1 (6.5–10.1)

 

P trend

 

0.57

 

Number of pack-years smoked

   ≤ 11 pack-years

82

10.0 (7.9–12.6)

 

   12–20 pack-years

85

8.5 (6.7–10.8)

 

   ≥ 21 pack-years

75

7.5 (5.9–9.6)

 

P trend

 

0.09

 

Age at smoking initiation

   ≥ 21 years

94

8.9 (7.1–11.1)

 

   18–20 years

114

8.4 (6.8–10.3)

 

   13–17 years

78

7.3 (5.8–9.3)

 

P trend

 

0.26

 

Smoking initiation before first birtha

   No

79

9.2 (7.2–11.8)

 

   Yes

186

7.8 (6.7–9.1)

 

P value

 

0.24

 

Time since smoking cessation

   ≥ 24 years

89

 

8.5 (6.7–10.7)

   12–23 years

89

 

5.2 (4.0–6.7)

   ≤ 11 years

88

 

6.5 (5.1–8.2)

P trend

  

0.12

  1. Analyses are adjusted for age at screening, age at first birth, number of children, age at menopause, postmenopausal hormone therapy use, and body mass index. Reported means are back-transformed from log-transformed estimated means. aAmong parous women only.