title: Physical activity and breast cancer risk in the College Alumni Health Study (United States).
abstract: OBJECTIVE
  It is unclear whether physical activity is associated with a reduced risk of breast cancer. Some studies also suggest different effects between pre- and postmenopausal women, and lean and heavy women.
  
  
  METHODS
  We followed 1,566 University of Pennsylvania alumnae (mean age, 45.5 years), initially free of breast cancer, from 1962 until 1993. Physical activity at baseline was assessed by asking women about stairs climbed, blocks walked, and sports played. We estimated energy expenditure and categorized women into approximate thirds (< 500, 500-999, 1,000+ kcal/wk). We identified 109 breast cancer cases during 35,365 person-years from follow-up questionnaires or from death certificates.
  
  
  RESULTS
  After adjustment for age and body mass index (BMI) (kg/m2), the relative risk (RR) of breast cancer was 0.92 (95 percent confidence interval [CI] = 0.58-1.45) among women expending 500-999 kcal/wk and 0.73 (CI = 0.46-1.14) for those expending 1,000+ kcal/wk, compared with women expending < 500 kcal/wk (P trend = 0.17). This association was modified by menopausal status, but not BMI. For postmenopausal women, corresponding RRs were 0.95 (CI = 0.58-1.57) and 0.49 (CI = 0.28-0.86), respectively (P trend = 0.015). Increased physical activity in premenopausal women was not significantly associated with decreased risk of breast cancer.
  
  
  CONCLUSIONS
  These data support an inverse association between physical activity and breast cancer among postmenopausal women.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA.
authors.forename: H D
authors.initials: HD
authors.lastname: Sesso
authors.forename: R S
authors.initials: RS
authors.lastname: Paffenbarger
authors.forename: I M
authors.initials: IM
authors.lastname: Lee
mesh_terms: D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D008593:Menopause; D008875:Middle Aged; D010809:Physical Fitness; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D014495:Universities / Q000706:statistics & numerical data