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. 2007 Oct 26;9(5):R73. doi: 10.1186/bcr1782

Table 3.

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

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

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.