Long term exposure to air pollution and asthma hospitalisations in older adults a cohort study
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Long term exposure to air pollution and asthma hospitalisations in older adults a cohort study

Long-term exposure to air pollution and asthmahospitalisationsin older adults: a cohort study

Zorana Jovanovic Andersen 27.09.2011 ERS

Conflict of interest disclosure

‘I have no, real or perceived, conflicts of interest that relate to this presentation’


  • Chronicinflammatorydisease of the airways, characterized by variable and recurring symptoms, reversible airflow obstruction, hyperresponsiveness, bronchospasm.


  • The prevalence of asthma in older adults is 6-10% in high-income countries, and increasing, including Denmark, where increase in the severity is also documented

  • The economic burden associated with hospital care, medications, and years of work lost is projected to escalate with increasing numbers of older people with asthma due to enhanced longevity

Background asthma air pollution
Background: Asthma & Air Pollution

  • Short-term exposure to elevated air pollution linked to exacerbation of asthma symptoms (wheezing, coughing, breathlessness) in children and adults, leading to asthma hospitalizations

  • More studies in children than adults: long-term exposure to air pollution in early life linked to development of asthma

  • Limited evidence in adults: does long-time/lifetime exposure to air pollution increases risk of asthma development in adult life?

Background asthma air pollution1
Background: Asthma & Air Pollution


- asthmaincidence and prevalencebased on self-reports of asthma

- loselydefinedonset, recall/info bias

- short air pollution exposurewindows

Aim of this study
Aim of thisstudy

  • We studied the association between traffic-related air pollution levels for up to 35 years at the residence and the risk for hospital admission for asthma in an elderly Danish cohort

  • We tested for an effect modification by lifestyle, education, and co-morbid conditions

Methods cohort
Methods - Cohort

  • Danish Diet, Cancer and Health cohort

  • 57 053 subjects, Copenhagen and Aarhus

  • Interviewed in 1993-1997 (baseline)

  • Age 50-65 years

  • Linkage to Central Population Registry and Danish Address Database - residential address history (1971)

  • Linkage to Danish National Patient Register (1979):

  • first-admission for asthma (ICD-10: J45-46), between baseline (1993-1997) and 27 June 2006

  • co-morbidities defined as hospitalizations for COPD (J40-44), ischemic heart disease (I20-25), and stroke (I60-63)

Methods air pollution exposure
Methods – Air Pollution Exposure

  • AirGIS dispersion model, sum of:

    1) regionalbackground, 2) urbanbackground, & 3) streetlevelcontribution

  • Input for AirGIS model

    • Street/building geometry

    • Street network and traffic data

    • Meteorology

Traffic counts, emission factors, density, speed, types, variation patterns over time

GIS Mapsbuildingheight,

streetwidth, opensector

Methods air pollution exposure1
Methods – Air Pollution Exposure

  • AirGIS Model output:

    • Annual mean NO2 /NOx

      concentrations at individual address

Flow and dispersion inside a street canyon

Methods statistical model
Methods – Statistical Model

  • Cox proportional hazards model, left truncation at age at baseline, and right censoring at age at hospital admission for asthma, death, emigration, or 27 June 2006

  • NO2 time-dependent variables, log transformed, mean since 1971 until asthma/censoring, estimates per IQR

  • Confounders: sex, smoking (status, intensity, duration, ETS), occupational exposures, BMI, educational level, fruit consumption

  • Effect modification: interaction term, Wald-test

  • Spline (rcs) in R, for dose-repsonse curve

Results study population
Results: Study Population

Outcome asthma hospitalization
Outcome: AsthmaHospitalization

  • Objective measure of asthma onset, nationwide register

  • Not marker of disease onset, but hallmark of asthma progression to a more severe stage or exacerbation

  • Traditionally confirmed by objective measurements of lung function and reversible airflow obstruction in Danish hospitals

  • The specificity of asthma as high as 0.98

  • Underestimates real asthma burden

Results descriptive statistics
Results: DescriptiveStatistics

Results exposure to air pollution
Results: Exposure to Air Pollution

Median NO2 for cohort15.2 µg/m3

and for asthmatics (n=977) 16.4 µg/m3

Results main analysis
Results: Main Analysis

Excluding 452 subjects

with prior COPD


1.11 (1.02-1.21)

1.10 (1.01-1.21)

1.29 (1.03-1.60)

Results effect modification
Results: EffectModification

Results dose response
Results: dose-response


  • The risk for asthma hospitalization in this elderly cohort was significantly positively associated with increasing levels of NO2 assessed over 35 years at their residences

  • The risk for new asthma hospitalizations about 10% per IQR

  • The risk was most pronounced for people with a previous asthma 41% per IQR or COPD hospitalization 31% per IQR.


  • No data on atopy, allergy, or familialhistory of asthma, importantrisk factors for asthma and potential effectmodifiers

  • Lack of workaddress, activity pattern, indoor air pollution sources, whichcould have imporved air pollution exposureassesment