title: Association between ambient air pollution and diabetes mellitus in Europe and North America: systematic review and meta-analysis.
abstract: BACKGROUND
  Air pollution is hypothesized to be a risk factor for diabetes. Epidemiological evidence is inconsistent and has not been systematically evaluated.
  
  
  OBJECTIVE
  We systematically reviewed epidemiological evidence on the association between air pollution and diabetes, and synthesized results of studies on type 2 diabetes mellitus (T2DM).
  
  
  METHODS
  We systematically searched electronic literature databases (last search, 29 April 2014) for studies reporting the association between air pollution (particle concentration or traffic exposure) and diabetes (type 1, type 2, or gestational). We systematically evaluated risk of bias and role of potential confounders in all studies. We synthesized reported associations with T2DM in meta-analyses using random-effects models and conducted various sensitivity analyses.
  
  
  RESULTS
  We included 13 studies (8 on T2DM, 2 on type 1, 3 on gestational diabetes), all conducted in Europe or North America. Five studies were longitudinal, 5 cross-sectional, 2 case-control, and 1 ecologic. Risk of bias, air pollution assessment, and confounder control varied across studies. Dose-response effects were not reported. Meta-analyses of 3 studies on PM2.5 (particulate matter ≤ 2.5 μm in diameter) and 4 studies on NO2 (nitrogen dioxide) showed increased risk of T2DM by 8-10% per 10-μg/m3 increase in exposure [PM2.5: 1.10 (95% CI: 1.02, 1.18); NO2: 1.08 (95% CI: 1.00, 1.17)]. Associations were stronger in females. Sensitivity analyses showed similar results.
  
  
  CONCLUSIONS
  Existing evidence indicates a positive association of air pollution and T2DM risk, albeit there is high risk of bias. High-quality studies assessing dose-response effects are needed. Research should be expanded to developing countries where outdoor and indoor air pollution are high.
authors.affiliation: Swiss Tropical and Public Health Institute, Basel, Switzerland.
authors.forename: Ikenna C
authors.initials: IC
authors.lastname: Eze
authors.forename: Lars G
authors.initials: LG
authors.lastname: Hemkens
authors.forename: Heiner C
authors.initials: HC
authors.lastname: Bucher
authors.forename: Barbara
authors.initials: B
authors.lastname: Hoffmann
authors.forename: Christian
authors.initials: C
authors.lastname: Schindler
authors.forename: Nino
authors.initials: N
authors.lastname: Künzli
authors.forename: Tamara
authors.initials: T
authors.lastname: Schikowski
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Probst-Hensch
mesh_terms: D000393:Air Pollutants / Q000633:toxicity*; D000397:Air Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D004781:Environmental Exposure / Q000009:adverse effects; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D009656:North America / Q000453:epidemiology; D052638:Particulate Matter / Q000009:adverse effects
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter