title: Prospective study of physical activity and risk of postmenopausal breast cancer.
abstract: BACKGROUND
  To prospectively examine the relation of total, vigorous and non-vigorous physical activity to postmenopausal breast cancer risk.
  
  
  METHODS
  We studied 32,269 women enrolled in the Breast Cancer Detection Demonstration Project Follow-up Study. Usual physical activity (including household, occupational and leisure activities) throughout the previous year was assessed at baseline using a self-administered questionnaire. Postmenopausal breast cancer cases were identified through self-reports, death certificates and linkage to state cancer registries. A Cox proportional hazards regression was used to estimate the relative risk and 95% confidence intervals of postmenopausal breast cancer associated with physical activity.
  
  
  RESULTS
  During 269,792 person-years of follow-up from 1987 to 1998, 1506 new incident cases of postmenopausal breast cancer were ascertained. After adjusting for potential risk factors of breast cancer, a weak inverse association between total physical activity and postmenopausal breast cancer was suggested (relative risk comparing extreme quintiles = 0.87; 95% confidence interval = 0.74 to 1.02; p for trend = 0.21). That relation was almost entirely contributed by vigorous activity (relative risk comparing extreme categories = 0.87; 95% confidence interval = 0.74 to 1.02; p for trend = 0.08). The inverse association with vigorous activity was limited to women who were lean (ie, body mass index <25.0 kg/m2: relative risk = 0.68; 95% confidence interval = 0.54 to 0.85). In contrast, no association with vigorous activity was noted among women who were overweight or obese (ie, body mass index > or = 25.0 kg/m2: relative risk = 1.18; 95% confidence interval = 0.93 to 1.49; p for interaction = 0.008). Non-vigorous activity showed no relation to breast cancer (relative risk comparing extreme quintiles = 1.02; 95% confidence interval = 0.87 to 1.19; p for trend = 0.86). The physical activity and breast cancer relation was not specific to a certain hormone receptor subtype.
  
  
  CONCLUSIONS
  In this cohort of postmenopausal women, breast cancer risk reduction appeared to be limited to vigorous forms of activity; it was apparent among normal weight women but not overweight women, and the relation did not vary by hormone receptor status. Our findings suggest that physical activity acts through underlying biological mechanisms that are independent of body weight control.
authors.affiliation: Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA. michael.leitzmann@klinik.uni-regensburg.de
authors.forename: Michael F
authors.initials: MF
authors.lastname: Leitzmann
authors.forename: Steven C
authors.initials: SC
authors.lastname: Moore
authors.forename: Tricia M
authors.initials: TM
authors.lastname: Peters
authors.forename: James V
authors.initials: JV
authors.lastname: Lacey
authors.forename: Arthur
authors.initials: A
authors.lastname: Schatzkin
authors.forename: Catherine
authors.initials: C
authors.lastname: Schairer
authors.forename: Louise A
authors.initials: LA
authors.lastname: Brinton
authors.forename: Demetrius
authors.initials: D
authors.lastname: Albanes
mesh_terms: D001943:Breast Neoplasms / Q000737:chemistry / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006184:Habits; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D009043:Motor Activity; D009363:Neoplasm Proteins / Q000032:analysis; D050177:Overweight / Q000453:epidemiology; D005082:Physical Exertion; D017698:Postmenopause; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D012306:Risk; D011795:Surveys and Questionnaires; D013851:Thinness / Q000453:epidemiology; D014481:United States / Q000453:epidemiology
chemical_list: D009363:Neoplasm Proteins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone