Table 3.
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.