title: Physical activity and breast cancer risk in Chinese women.
abstract: BACKGROUND
  The influence of different types and intensities of physical activity on risk for breast cancer is unclear.
  
  
  METHODS
  In a prospective cohort of 73,049 Chinese women (40-70 years), who had worked outside the home, we studied breast cancer risk in relation to specific types of self-reported and work history-related physical activity, including adolescent and adult exercise and household activity and walking and cycling for transportation. Occupational sitting time and physical activity energy expenditure were assigned based on lifetime occupational histories.
  
  
  RESULTS
  In all, 717 incident breast cancer cases were diagnosed. Breast cancer risk was lower for women in the lowest quartile of average occupational sitting time and in the highest quartile of average occupational energy expenditure (adjusted hazard ratio (HR): 0.81 and 0.73, respectively, P ≤ 0.05). Adult exercise at or above the recommended level (8 metabolic equivalent (MET) h per week per year) was associated with lower risk (adjusted HR: 0.73, P<0.05) in post-menopausal women. Analysis of joint effects showed that having both an active job and exercise participation did not confer an additional benefit. Other common daily activities were not associated with lower risk.
  
  
  CONCLUSIONS
  These findings suggest that both exercise and occupational activity are associated with lower breast cancer risk, which supports current health promotion campaigns promoting exercise.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD 20892, USA.
authors.forename: A
authors.initials: A
authors.lastname: Pronk
authors.forename: B-T
authors.initials: BT
authors.lastname: Ji
authors.forename: X-O
authors.initials: XO
authors.lastname: Shu
authors.forename: W-H
authors.initials: WH
authors.lastname: Chow
authors.forename: S
authors.initials: S
authors.lastname: Xue
authors.forename: G
authors.initials: G
authors.lastname: Yang
authors.forename: H-L
authors.initials: HL
authors.lastname: Li
authors.forename: N
authors.initials: N
authors.lastname: Rothman
authors.forename: Y-T
authors.initials: YT
authors.lastname: Gao
authors.forename: W
authors.initials: W
authors.lastname: Zheng
authors.forename: C E
authors.initials: CE
authors.lastname: Matthews
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D001943:Breast Neoplasms; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009043:Motor Activity; D009790:Occupations; D011446:Prospective Studies; D057185:Sedentary Behavior; D016138:Walking