title: Major air pollutants and risk of COPD exacerbations: a systematic review and meta-analysis.
abstract: BACKGROUND
  Short-term exposure to major air pollutants (O3, CO, NO2, SO2, PM10, and PM2.5) has been associated with respiratory risk. However, evidence on the risk of chronic obstructive pulmonary disease (COPD) exacerbations is still limited. The present study aimed at evaluating the associations between short-term exposure to major air pollutants and the risk of COPD exacerbations.
  
  
  METHODS
  After a systematic search up until March 30, 2016, in both English and Chinese electronic databases such as PubMed, EMBASE, and CNKI, the pooled relative risks and 95% confidence intervals were estimated by using the random-effects model. In addition, the population-attributable fractions (PAFs) were also calculated, and a subgroup analysis was conducted. Heterogeneity was assessed byI2.
  
  
  RESULTS
  In total, 59 studies were included. In the single-pollutant model, the risks of COPD were calculated by each 10 μg/m3increase in pollutant concentrations, with the exception of CO (100 μg/m3). There was a significant association between short-term exposure and COPD exacerbation risk for all the gaseous and particulate pollutants. The associations were strongest at lag0 and lag3 for gaseous and particulate air pollutants, respectively. The subgroup analysis not only further confirmed the overall adverse effects but also reduced the heterogeneities obviously. When 100% exposure was assumed, PAFs ranged from 0.60% to 4.31%, depending on the pollutants. The adverse health effects of SO2and NO2exposure were more significant in low-/middle-income countries than in high-income countries: SO2, relative risk: 1.012 (95% confidence interval: 1.001, 1.023); and NO2, relative risk: 1.019 (95% confidence interval: 1.014, 1.024).
  
  
  CONCLUSIONS
  Short-term exposure to air pollutants increases the burden of risk of COPD acute exacerbations significantly. Controlling ambient air pollution would provide benefits to COPD patients.
authors.affiliation: Shenzhen Institute of Research and Innovation, Nanshan, The University of Hong Kong, Shenzhen, People's Republic of China; School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Jinhui
authors.initials: J
authors.lastname: Li
authors.affiliation: Shenzhen Institute of Research and Innovation, Nanshan, The University of Hong Kong, Shenzhen, People's Republic of China; School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Shengzhi
authors.initials: S
authors.lastname: Sun
authors.affiliation: Shenzhen Institute of Research and Innovation, Nanshan, The University of Hong Kong, Shenzhen, People's Republic of China; School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Robert
authors.initials: R
authors.lastname: Tang
authors.affiliation: School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Hong
authors.initials: H
authors.lastname: Qiu
authors.affiliation: Department of Thoracic Surgery, Shanghai Chest Hospital, Shanghai Jiao Tong University, Minhang, Shanghai, People's Republic of China.
authors.forename: Qingyuan
authors.initials: Q
authors.lastname: Huang
authors.affiliation: School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Tonya G
authors.initials: TG
authors.lastname: Mason
authors.affiliation: Shenzhen Institute of Research and Innovation, Nanshan, The University of Hong Kong, Shenzhen, People's Republic of China; School of Public Health, The University of Hong Kong, Pok Fu Lam, Hong Kong Special Administrative Region.
authors.forename: Linwei
authors.initials: L
authors.lastname: Tian
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000393:Air Pollutants / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D019570:Inhalation Exposure / Q000009:adverse effects*; D008168:Lung / Q000187:drug effects* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult
chemical_list: D000393:Air Pollutants
keywords: COPD exacerbations; acute exposure; air pollution; meta-analysis