Physical activity and change in mammographic density

Shannon M. Conroy, Lesley M. Butler, Danielle J Harvey, Ellen B Gold, Barbara Sternfeld, Nina Oestreicher, Gail A. Greendale, Laurel A. Habel

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


One potential mechanism by which physical activity may protect against breast cancer is by decreasing mammographic density. Percent mammographic density, the proportion of dense breast tissue area to total breast area, declines with age and is a strong risk factor for breast cancer. The authors hypothesized that women who were more physically active would have a greater decline in percent mammographic density with age, compared with less physically active women. The authors tested this hypothesis using longitudinal data (1996-2004) from 722 participants in the Study of Women's Health Across the Nation (SWAN), a multiethnic cohort of women who were pre- and early perimenopausal at baseline, with multivariable, repeated-measures linear regression analyses. During an average of 5.6 years, the mean annual decline in percent mammographic density was 1.1% (standard deviation = 0.1). A 1-unit increase in total physical activity score was associated with a weaker annual decline in percent mammographic density by 0.09% (standard error = 0.03; P = 0.01). Physical activity was inversely associated with the change in nondense breast area (P < 0.01) and not associated with the change in dense breast area (P = 0.17). Study results do not support the hypothesis that physical activity reduces breast cancer through a mechanism that includes reduced mammographic density.

Original languageEnglish (US)
Pages (from-to)960-968
Number of pages9
JournalAmerican Journal of Epidemiology
Issue number9
StatePublished - May 2010


  • breast neoplasms
  • exercise
  • longitudinal studies
  • mammography
  • physical fitness
  • risk factors

ASJC Scopus subject areas

  • Epidemiology


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