Table 1.

Age-adjusted proportion of person-years for breast cancer risk factors according to oral contraceptive use, among women followed-up in the Nurses' Health Study II population (n = 116,413 women aged 24-43 y in 1989)

Oral contraceptive use
Never (%)Past (%)Current (%)
Age at menarche (y)
    <12242522
    13272728
    ≥14191719
Parity
    None321938
    1121719
    2293931
    318199
    ≥4962
Age at first birth (y)
    ≤24394238
    >3011912
Family history of breast cancer
    Yes765
Benign breast disease
    Yes, biopsy confirmed12138
BMI (kg/m2)
    <21211927
    21 to <23192024
    23 to <25161718
    25 to <30212219
    ≥30191711
Alcohol intake
    None544438
    1 to <5 g/d222429
    5 to <15111419
    ≥15 g/d244
Animal fat intake (quintiles)
    Quintile 1 (lowest)171515
    Quintile 3151514
    Quintile 5 (highest)141513
Smoking
    Never776271
    Past162520
    Current7139
Ovulatory infertility
    Yes773
Menstrual cycle irregularity
    Regular777372
    Very irregular777
Total breast-feeding duration (mo)
    None131615
    <1455
    4-691113
    ≥12524136