Reproductive and hormonal factors associated with mammographic breast density by age (United States)

Cancer Causes Control. 2000 Dec;11(10):955-63. doi: 10.1023/a:1026514032085.


Objectives: We determined the association of certain reproductive and hormonal factors with breast density over decades of life.

Methods: Subjects were women age 20-79 years who had a screening mammogram between 1 June 1996 and 1 August 1997, in Seattle, Washington. Women with increased breast density (upper two categories of BI-RADS terminology) (n = 14,432) were compared to those with fatty breasts (lower two categories (n = 14,552). Unconditional logistic regression was used with adjustment for age at mammogram, parity, age at first birth, menopausal status, current use of hormone replacement therapy (HRT), and body mass index.

Results: The association of nulliparity with density was evident for women at all ages (odds ratio (OR) and 95% confidence interval (CI) = 1.5 (1.3-1.7) and 1.6 (1.4-1.9) for women age < or = 45 and > 65, respectively). Older age at first birth was more strongly associated with density among women > 55 than among younger women. The association of current use of HRT with density, but not of former use, increased with age when compared to never users (OR = 1.4 (1.2-1.7) and 2.2 (2.0-2.5) for women age 46-55 and > 65, respectively).

Conclusions: Results suggest that pregnancy at an early age has a permanent beneficial association with density, while HRT has a transitory adverse association.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adipose Tissue
  • Adult
  • Aged
  • Aging*
  • Body Mass Index
  • Breast / anatomy & histology*
  • Breast / physiology
  • Breast Neoplasms / diagnostic imaging*
  • Breast Neoplasms / etiology
  • Female
  • Hormone Replacement Therapy
  • Humans
  • Mammography*
  • Menopause
  • Middle Aged
  • Parity
  • Pregnancy
  • Reference Values
  • Risk Factors