title: A study of the combined effects of physical activity and air pollution on mortality in elderly urban residents: the Danish Diet, Cancer, and Health Cohort.
abstract: BACKGROUND
  Physical activity reduces, whereas exposure to air pollution increases, the risk of premature mortality. Physical activity amplifies respiratory uptake and deposition of air pollutants in the lung, which may augment acute harmful effects of air pollution during exercise.
  
  
  OBJECTIVE
  We aimed to examine whether benefits of physical activity on mortality are moderated by long-term exposure to high air pollution levels in an urban setting.
  
  
  METHODS
  A total of 52,061 subjects (50-65 years of age) from the Danish Diet, Cancer, and Health cohort, living in Aarhus and Copenhagen, reported data on physical activity in 1993-1997 and were followed until 2010. High exposure to air pollution was defined as the upper 25th percentile of modeled nitrogen dioxide (NO2) levels at residential addresses. We associated participation in sports, cycling, gardening, and walking with total and cause-specific mortality by Cox regression, and introduced NO2 as an interaction term.
  
  
  RESULTS
  In total, 5,534 subjects died: 2,864 from cancer, 1,285 from cardiovascular disease, 354 from respiratory disease, and 122 from diabetes. Significant inverse associations of participation in sports, cycling, and gardening with total, cardiovascular, and diabetes mortality were not modified by NO2. Reductions in respiratory mortality associated with cycling and gardening were more pronounced among participants with moderate/low NO2 [hazard ratio (HR) = 0.55; 95% CI: 0.42, 0.72 and 0.55; 95% CI: 0.41, 0.73, respectively] than with high NO2 exposure (HR = 0.77; 95% CI: 0.54, 1.11 and HR = 0.81; 95% CI: 0.55, 1.18, p-interaction = 0.09 and 0.02, respectively).
  
  
  CONCLUSIONS
  In general, exposure to high levels of traffic-related air pollution did not modify associations, indicating beneficial effects of physical activity on mortality. These novel findings require replication in other study populations.
authors.affiliation: Center for Epidemiology and Screening, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Zorana Jovanovic
authors.initials: ZJ
authors.lastname: Andersen
authors.forename: Audrey
authors.initials: A
authors.lastname: de Nazelle
authors.forename: Michelle Ann
authors.initials: MA
authors.lastname: Mendez
authors.forename: Judith
authors.initials: J
authors.lastname: Garcia-Aymerich
authors.forename: Ole
authors.initials: O
authors.lastname: Hertel
authors.forename: Anne
authors.initials: A
authors.lastname: Tjønneland
authors.forename: Kim
authors.initials: K
authors.lastname: Overvad
authors.forename: Ole
authors.initials: O
authors.lastname: Raaschou-Nielsen
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Nieuwenhuijsen
mesh_terms: D000368:Aged; D000397:Air Pollution / Q000009:adverse effects*; D002318:Cardiovascular Diseases / Q000401:mortality*; D002947:Cities; D003718:Denmark / Q000453:epidemiology; D003920:Diabetes Mellitus / Q000401:mortality; D005260:Female; D051639:Gardening; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000401:mortality*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012044:Regression Analysis; D012140:Respiratory Tract Diseases / Q000401:mortality*; D013177:Sports; D016138:Walking