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 | Â | 0.008 | Â |
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 | Â | 0.57 | Â |
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 | Â | 0.09 | Â |
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 | Â | 0.26 | Â |
Smoking initiation before first birtha | |||
   No | 79 | 9.2 (7.2–11.8) |  |
   Yes | 186 | 7.8 (6.7–9.1) |  |
P value | Â | 0.24 | Â |
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 | Â | Â | 0.12 |