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Thorax 62:957-963 doi:10.1136/thx.2007.078964
  • Asthma

Relationship between air pollution, lung function and asthma in adolescents

  1. Talat Islam,
  2. W James Gauderman,
  3. Kiros Berhane,
  4. Rob McConnell,
  5. Ed Avol,
  6. John M Peters,
  7. Frank D Gilliland
  1. Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
  1. Dr Frank Gilliland, Department of Preventive Medicine, Keck School of Medicine, 1540 Alcazar Street, CHP 236, Los Angeles, California 90033, USA; gillilan{at}usc.edu
  • Received 28 February 2007
  • Accepted 18 April 2007
  • Published Online First 21 May 2007

Abstract

Background: The interrelationships between air pollution, lung function and the incidence of childhood asthma have yet to be established. A study was undertaken to determine whether lung function is associated with new onset asthma and whether this relationship varies by exposure to ambient air pollutants.

Methods: A cohort of children aged 9–10 years without asthma or wheeze at study entry were identified from the Children’s Health Study and followed for 8 years. The participants resided in 12 communities with a wide range of ambient air pollutants that were measured continuously. Spirometric testing was performed and a medical diagnosis of asthma was ascertained annually. Proportional hazard regression models were fitted to investigate the relationship between lung function at study entry and the subsequent development of asthma and to determine whether air pollutants modify these associations.

Results: The level of airway flow was associated with new onset asthma. Over the 10th–90th percentile range of forced expiratory flow over the mid-range of expiration (FEF25–75, 57.1%), the hazard ratio (HR) of new onset asthma was 0.50 (95% CI 0.35 to 0.71). This protective effect of better lung function was reduced in children exposed to higher levels of particulate matter with an aerodynamic diameter <2.5 μm (PM2.5). Over the 10th–90th percentile range of FEF25–75, the HR of new onset asthma was 0.34 (95% CI 0.21 to 0.56) in communities with low PM2.5 (<13.7 μg/m3) and 0.76 (95% CI 0.45 to 1.26) in communities with high PM2.5 (⩾13.7 μg/m3). A similar pattern was observed for forced expiratory volume in 1 s. Little variation in HR was observed for ozone.

Conclusion: Exposure to high levels of PM2.5 attenuates the protective effect of better lung function against new onset asthma.

Footnotes

  • This work was supported by the Southern California Environmental Health Sciences Center (grant number 5P30ES007048) funded by the National Institute of Environmental Health Sciences; the Children’s Environmental Health Center (grant numbers 5P01ES009581, R826708-01 and RD831861-01) funded by the National Institute of Environmental Health Sciences and the Environmental Protection Agency; the National Institute of Environmental Health Sciences (grant number 5P01ES011627); the National Heart, Lung and Blood Institute (grant numbers 5R01HL61768 and 1R01HL76647); the California Air Resources Board (contract number 94-331); and the Hastings Foundation. The study sponsors had no role in the study design; the collection, analysis and interpretation of data; the writing of the report; or in the decision to submit the paper for publication.

  • Competing interests: None.

  • Abbreviations:
    FEF25–75
    forced expiratory flow over the mid-range of expiration
    FEV1
    forced expiratory volume in 1 s
    FVC
    forced vital capacity
    NO2
    nitrogen dioxide
    O3
    ozone
    PM10
    PM2.5, particulate matter with an aerodynamic diameter <10 µm and <2.5 µm