title: Physical activity and risk of rheumatoid arthritis in women: a population-based prospective study.
abstract: BACKGROUND
  Only one study has analysed the association between exercise and development of rheumatoid arthritis (RA), showing no association. Aim of this paper was to evaluate the association of physical activity in all its aspect with RA.
  
  
  METHODS
  To examine this association, middle age and elderly women from the Swedish Mammography Cohort, a population-based prospective study, were analysed. Data on physical activity were collected in 1997 by self-administrated food-frequency questionnaire. Risk of RA associated with physical activity was estimated using Cox proportional hazard regression models.
  
  
  RESULTS
  Among 30,112 women born between 1914 and 1948 followed-up from January 1, 2003 to December 31, 2010, 201 RA cases were identified (226,477 person-years). There was a statistically significant 35% lower risk of RA (relative risk (RR), 0.65; 95% confidence interval (CI), 0.43-0.96) among women in the highest category of leisure-time activity (combining more than 20 minute per day of walking/bicycling (median 40-60 minute per day) and more than 1 hour per week of exercise (median 2-3 hours per week)) as compared to women in the lowest category (less than 20 minute per day of walking/bicycling and less than 1 hour per week of exercise). A non-statistically significant decreased risk was observed for household work (-32%) and work/occupation (-15%), while an increased risk was observed for leisure-time physical inactivity (+27%). Daily energy expenditure was not associated with risk of RA.
  
  
  CONCLUSIONS
  This prospective population-based cohort study of women supports the hypothesis that physical activity can be a protective factor in the etiology of rheumatoid arthritis. Our results add to accumulated evidence on benefits of modifiable leisure-time physical activity for prevention of many other chronic diseases.
authors.affiliation: Division of Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Nobels vag 13, Stockholm, 171 77, Sweden. daniela.digiuseppe@ki.se.
authors.forename: Daniela
authors.initials: D
authors.lastname: Di Giuseppe
authors.affiliation: Division of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Nobels vag 13, Stockholm, 171 77, Sweden. matteo.bottai@ki.se.
authors.forename: Matteo
authors.initials: M
authors.lastname: Bottai
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden. johan.askling@ki.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Askling
authors.affiliation: Division of Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Nobels vag 13, Stockholm, 171 77, Sweden. alicja.wolk@ki.se.
authors.forename: Alicja
authors.initials: A
authors.lastname: Wolk
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000453:epidemiology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D009043:Motor Activity / Q000502:physiology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D016138:Walking / Q000502:physiology*