title: Associations between lifestyle and air pollution exposure: Potential for confounding in large administrative data cohorts.
abstract: Cohorts based on administrative data have size advantages over individual cohorts in investigating air pollution risks, but often lack in-depth information on individual risk factors related to lifestyle. If there is a correlation between lifestyle and air pollution, omitted lifestyle variables may result in biased air pollution risk estimates. Correlations between lifestyle and air pollution can be induced by socio-economic status affecting both lifestyle and air pollution exposure.
  
  
  
  Our overall aim was to assess potential confounding by missing lifestyle factors on air pollution mortality risk estimates. The first aim was to assess associations between long-term exposure to several air pollutants and lifestyle factors. The second aim was to assess whether these associations were sensitive to adjustment for individual and area-level socioeconomic status (SES), and whether they differed between subgroups of the population. Using the obtained air pollution-lifestyle associations and indirect adjustment methods, our third aim was to investigate the potential bias due to missing lifestyle information on air pollution mortality risk estimates in administrative cohorts.
  
  
  
  We used a recent Dutch national health survey of 387,195 adults to investigate the associations of PM10, PM2.5, PM2.5-10, PM2.5absorbance, OPDTT,OPESRand NO2annual average concentrations at the residential address from land use regression models with individual smoking habits, alcohol consumption, physical activity and body mass index. We assessed the associations with and without adjustment for neighborhood and individual SES characteristics typically available in administrative data cohorts. We illustrated the effect of including lifestyle information on the air pollution mortality risk estimates in administrative cohort studies using a published indirect adjustment method.
  
  
  
  Current smoking and alcohol consumption were generally positively associated with air pollution. Physical activity and overweight were negatively associated with air pollution. The effect estimates were small (mostly <5% of the air pollutant standard deviations). Direction and magnitude of the associations depended on the pollutant, use of continuous vs. categorical scale of the lifestyle variable, and level of adjustment for individual and area-level SES. Associations further differed between subgroups (age, sex) in the population. Despite the small associations between air pollution and smoking intensity, indirect adjustment resulted in considerable changes of air pollution risk estimates for cardiovascular and especially lung cancer mortality.
  
  
  
  Individual lifestyle-related risk factors were weakly associated with long-term exposure to air pollution in the Netherlands. Indirect adjustment for missing lifestyle factors in administrative data cohort studies may substantially affect air pollution mortality risk estimates.
authors.affiliation: Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, Netherlands. Electronic address: m.m.strak@uu.nl.
authors.forename: Maciej
authors.initials: M
authors.lastname: Strak
authors.affiliation: National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands.
authors.forename: Nicole
authors.initials: N
authors.lastname: Janssen
authors.affiliation: National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands.
authors.forename: Rob
authors.initials: R
authors.lastname: Beelen
authors.affiliation: Department of Physical Geography, Faculty of Geosciences, Utrecht University, Netherlands.
authors.forename: Oliver
authors.initials: O
authors.lastname: Schmitz
authors.affiliation: Department of Physical Geography, Faculty of Geosciences, Utrecht University, Netherlands.
authors.forename: Derek
authors.initials: D
authors.lastname: Karssenberg
authors.affiliation: National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands.
authors.forename: Danny
authors.initials: D
authors.lastname: Houthuijs
authors.affiliation: National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands.
authors.forename: Carolien
authors.initials: C
authors.lastname: van den Brink
authors.affiliation: Department of Human Geography and Spatial Planning, Faculty of Geosciences, Utrecht University, Netherlands.
authors.forename: Martin
authors.initials: M
authors.lastname: Dijst
authors.affiliation: Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, Netherlands; Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, Netherlands.
authors.forename: Bert
authors.initials: B
authors.lastname: Brunekreef
authors.affiliation: Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, Netherlands.
authors.forename: Gerard
authors.initials: G
authors.lastname: Hoek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis*; D015331:Cohort Studies; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008019:Life Style / Q000208:ethnology; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009426:Netherlands / Q000453:epidemiology; D052638:Particulate Matter / Q000032:analysis; D018570:Risk Assessment; D012923:Social Class; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter