Table 1.
Characteristics of the study population (n = 907) by smoking status
| Characteristic | Smoking status | P valuea | ||
| Current smokers (n = 310) | Former smokers (n = 279) | Never smokers (n = 318) | ||
| Age at screening (years) | 60.7 (4.4) | 61.6 (4.5) | 61.9 (4.6) | <0.001 |
| Age at menarche (years) | 13.3 (1.4) | 13.3 (1.4) | 13.3 (1.4) | 0.47 |
| Age at first birthb (years) | 22.3 (3.6) | 22.7 (3.3) | 23.5 (3.9) | <0.001 |
| Number of childrenb | 2.9 (1.2) | 2.8 (1.1) | 2.9 (1.4) | 0.82 |
| Education (years) | 9.4 (3.2) | 9.7 (3.4) | 10.2 (3.6) | 0.02 |
| Age at menopause (years) | 47.5 (5.5) | 48.8 (4.8) | 49.1 (4.8) | <0.001 |
| Body mass index (kg/m2) | 26.1 (4.4) | 28.4 (5.1) | 27.6 (4.7) | <0.001 |
| Alcohol consumptionc (g/day) | 3.8 (3.8) | 4.0 (3.9) | 3.4 (4.0) | 0.36 |
| Ever oral contraceptive use (%) | 54.8 | 49.5 | 37.4 | <0.001 |
| Parous (%) | 93.6 | 93.6 | 90.3 | 0.13 |
| Ever postmenopausal hormone therapy use (%) | 43.2 | 45.2 | 41.8 | 0.72 |
| Breast cancer in first-degree relative (%) | 6.8 | 9.3 | 9.8 | 0.18 |
Data presented as the mean (standard deviation) or as the frequency. aCurrent smokers versus never smokers. bAmong parous women only.cAmong alcohol drinkers only.