title: Active, but not passive cigarette smoking was inversely associated  with mammographic density.
abstract: OBJECTIVE
  The opposing carcinogenic and antiestrogenic properties of tobacco smoke may explain why epidemiologic studies have not consistently reported positive associations for active smoking and breast cancer risk. A negative relation between mammographic density, a strong breast cancer risk factor, and active smoking would lend support for an antiestrogenic mechanism.
  
  
  METHODS
  We used multivariable linear regression to assess the associations of active smoking and secondhand smoke (SHS) exposure with mammographic density in 799 pre- and early perimenopausal women in the Study of Women's Health Across the Nation (SWAN).
  
  
  RESULTS
  We observed that current active smoking was associated with 7.2% lower mammographic density, compared to never active smoking and no SHS exposure (p = 0.02). Starting to smoke before 18 years of age and having smoked > or =20 cigarettes/day were also associated with statistically significantly lower percent densities. Among nulliparous women having smoked > or =20 cigarettes/day was associated with 23.8% lower density, compared to having smoked < or = 9 cigarettes/day (p<0.001).
  
  
  CONCLUSIONS
  Our findings support the hypothesis that tobacco smoke exerts an antiestrogenic effect on breast tissue, but counters the known increased risk of breast cancer with smoking prior to first full-term birth. Thus, our data suggest that the antiestrogenic but not the carcinogenic effects of smoking may be reflected by breast density.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523-1681, USA. Lesley.Butler@colostate.edu
authors.forename: Lesley M
authors.initials: LM
authors.lastname: Butler
authors.forename: Ellen B
authors.initials: EB
authors.lastname: Gold
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Conroy
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Crandall
authors.forename: Gail A
authors.initials: GA
authors.lastname: Greendale
authors.forename: Nina
authors.initials: N
authors.lastname: Oestreicher
authors.forename: Charles P
authors.initials: CP
authors.lastname: Quesenberry
authors.forename: Laurel A
authors.initials: LA
authors.lastname: Habel
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data; D044466:Asian People / Q000706:statistics & numerical data; D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000175:diagnosis / Q000209:etiology; D004965:Estrogen Antagonists / Q000009:adverse effects; D005260:Female; D006801:Humans; D016014:Linear Models; D008327:Mammography / Q000379:methods*; D008875:Middle Aged; D015999:Multivariate Analysis; D010298:Parity; D011247:Pregnancy; D018570:Risk Assessment / Q000706:statistics & numerical data; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D011795:Surveys and Questionnaires; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*; D044465:White People / Q000706:statistics & numerical data; D016387:Women's Health / Q000208:ethnology
chemical_list: D004965:Estrogen Antagonists; D014028:Tobacco Smoke Pollution