title: Lifetime physical activity and the incidence of proliferative benign breast disease.
abstract: BACKGROUND
  Exercise is a modifiable factor that is inversely related to risk for breast cancer. To determine if physical activity has a preventative effect on development of premalignant breast lesions, we examined the association between exercise and the incidence of proliferative benign breast disease.
  
  
  METHODS
  In 1997, the Nurses' Health Study II cohort reported levels of physical activity during adolescence and adulthood using a validated recall instrument. We followed 40,318 participants free from benign breast disease (BBD) or cancer prospectively for four years and confirmed 232 proliferative benign breast lesions by centralized pathology review. Cox proportional hazards models estimated the age-adjusted and multivariable-adjusted relative risks for physical activity and proliferative benign breast disease.
  
  
  RESULTS
  We observed a significant inverse association for walking and incidence of BBD, risk was reduced by 9% per hour of walking (95% CI 0% to 17%), (p trend = 0.05). Despite a small number of cases, risk of columnar cell lesions also suggested an inverse association with strenuous activity (RR for 4 or more hours of strenuous activity per week = 0.62; 0.31-1.22 compared to < 1 h per week).
  
  
  CONCLUSIONS
  This study suggests that exercise may be inversely associated with the risk of developing proliferative benign breast disease, one of the earliest steps in the development of breast cancer.
authors: Alvin J. Siteman Cancer Center and Department of Surgery, Washington University School of Medicine, St. Louis, MO, USA.
authors: Michelle M
authors: MM
authors: Jung
authors: Graham A
authors: GA
authors: Colditz
authors: Laura C
authors: LC
authors: Collins
authors: Stuart J
authors: SJ
authors: Schnitt
authors: James L
authors: JL
authors: Connolly
authors: Rulla M
authors: RM
authors: Tamimi
mesh_terms: D000328:Adult; D001941:Breast Diseases / Q000453:epidemiology; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008875:Middle Aged; D011230:Precancerous Conditions / Q000453:epidemiology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology