Table 1 Age-adjusted characteristics of study participants by case/control status: Nurses' Health Study, 1999 to 2009
| Â | Cases (n= 634) | Controls (n= 1,264) |
|---|---|---|
Age at blood collection* | 43.5 (4.0) | 43.3 (3.9) |
BMI (kg/m2) at blood collection | 24.9 (4.8) | 25.7 (5.9) |
BMI (kg/m2) at age 18 | 20.8 (2.9) | 21.1 (3.0) |
Age at menarche | 12.4 (1.3) | 12.5 (1.4) |
Parous, % | 80 | 81 |
Age at first birth** | 27.4 (4.5) | 26.7 (4.5) |
Luteal day, prior to next cycle | 8.4 (3.1) | 8.4 (2.9) |
Follicular day, after cycle start | 4.0 (0.8) | 4.0 (1.3) |
Menopausal status at diagnosis | Â | Â |
   Premenopausal, % | 67 | 69 |
   Postmenopausal, % | 23 | 23 |
   Perimenopausal/Unknown, % | 10 | 8 |
Family history of breast cancer, % | 18 | 10 |
History of benign breast disease, % | 22 | 14 |