Table 1.

Age and age-adjusted characteristics of the study population at blood draw according to categories of mammographic density, Nurses' Health Study (1989-1990)

Mammographic density (%)
Range
<10
10.0-25.0
>25.0
No. women188175157
Mean
    Age at blood draw, y61.361.861.3
    Age at mammogram, y63.063.062.7
    Age at menarche, y12.612.512.8
    Age at first birth, y24.725.425.9
    Age at menopause*, y50.650.949.8
    Time since menopause*, y12.212.814.0
    Parity3.73.53.1
    Alcohol consumption, g2.42.92.8
    BMI, kg/m228.726.123.4
Frequency (%)
    Nulliparous4.36.911.5
    History of benign breast disease30.634.639.0
    Past postmenopausal hormone use34.038.946.2
    Current smoker14.212.911.5
    Family history of breast cancer12.414.415.8
    Natural menopause74.372.466.2
    Bilateral oophorectomy9.18.312.7
  • * Among those with a natural menopause.

  • Among parous women only.