title: Breast cancer risk and lifetime leisure-time and occupational physical activity (Sweden).
abstract: OBJECTIVE
  To clarify whether type and timing of physical activity affect postmenopausal breast cancer risk.
  
  
  METHODS
  In a population-based case-control study within the Swedish female population 50-74 years of age, 3347 women with invasive, postmenopausal breast cancer (84% of all eligible) and 3455 controls (82% of all selected) reported on past leisure-time physical activity. Record linkage to decennial census data (1960-1990) provided estimates of their occupational physical activity. Odds ratios with 95% confidence intervals were estimated by multivariate logistic regression.
  
  
  RESULTS
  After adjustment for potential confounders, women in sedentary occupations during their reproductive years (25-44 years of age) had a 50% higher risk for postmenopausal breast cancer, compared to those with the physically most demanding jobs. Only the most recent leisure-time physical activity was associated with a significant risk reduction. Women with the combination of sedentary jobs and lack of leisure-time exercise had a three-fold higher risk of breast cancer, compared to the physically most active both inside and outside the workplace.
  
  
  CONCLUSIONS
  Effects of occupational and leisure-time physical activity on breast cancer risk appear to have different latency times, and/or to be effect-modified by age or reproductive status. Although chance might explain our findings, it is advisable to consider type and timing of physical activity in future studies.
authors.affiliation: Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden. Tahereh.Moradi@mep.ki.se
authors.forename: T
authors.initials: T
authors.lastname: Moradi
authors.forename: O
authors.initials: O
authors.lastname: Nyrén
authors.forename: M
authors.initials: M
authors.lastname: Zack
authors.forename: C
authors.initials: C
authors.lastname: Magnusson
authors.forename: I
authors.initials: I
authors.lastname: Persson
authors.forename: H O
authors.initials: HO
authors.lastname: Adami
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D016022:Case-Control Studies; D015444:Exercise; D005260:Female; D006801:Humans; D007899:Leisure Activities; D016015:Logistic Models; D008875:Middle Aged; D009790:Occupations; D016017:Odds Ratio; D017698:Postmenopause; D017584:Reproductive History; D012307:Risk Factors; D012923:Social Class; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology